Intel 8080 8085 assembly language programming 1977 intel

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I ---------------,1
r-I

8080/8085 ASSEMBLY LANGUAGE
PROGRAMMING MANUAL

Copyright © 1977,1978 Intel Corporation

Intel Corporation, 3065 Bowers Avenue, Santa Clara, California 95051

PREFACE

This manual describes programming with Intel's assembly language. It will not teach you how to program a computer.

Although this manual is designed primarily for reference, It also contains some instructional matenal to help the beginning
programmer. The manual is organized as follows:

Chapter 1. ASSEMBLY LANGUAGE AND PROCESSORS

Description of the assembler
Overview of 8080 hardware and instruction set
Description of 8080(8085 differences

Chapter 2. ASSEMBLY LANGUAGE CONCEPTS

General assembly language coding rules

Chapter 3. INSTRUCTION SET

Descriptions of each instruction (these are listed alphabetically
for quick reference)

Chapter 4. ASSEMBLER DIRECTIVES

Data definition
Conditional assembly
Relocation

Chapter 5. MACROS

Macro directives
Macro examples

Chapter 6. PROGRAMMING TECHNIQUES

Programming examples

Chapter 7, INTERRUPTS

Description of the Interrupt system.

Chapters 3 and 4 will fill most of the experienced programmer's reference requirements. Use the table of contents or the
index to locate information quickly,

The beginning programmer should read Chapters 1 and 2 and then skip to the examples in Chapter 6. As these examples
raise questions, refer to the appropriate information in Chapter 3 or 4. Before writing a program, you will need to read
Chapter 4. The 'Programming Tips' in Chapter 4 are intended especially for the beginning programmer.

iii

RELATED PUBLICATIONS

To use your Intellec development system effectively, you should be familiar with the following Intel
publications:

ISIS-II 8080/8085 IAACRO ASSEMBLER OPERATOR'S MANUAL, 9800292

When you activate the assembler, you have the option of specifying a number of controls. The operator's
manual descriJes the activation sequence for the assembler. The manual also describes the debugging tools
and the error messages supplied by the assembler.

ISIS-II SYSTEM U~;ER'S GUIDE, 9800306

User program; are commonly stored on diskette files. The ISIS-II User's GUide describes the use of the text
editor for entering and maintaining programs. The manual also describes the procedures for linking and
locating reloc Itable program modules.

Hardware Referenc~s

For addition21 information about processors and their related components, refer to the appropriate User's
Manual:

8080 MICROCOMPUTER SYSTEMS USER'S MANU,A,L, 9800153

8085 MICROCOMPUTER SYSTEMS USER'S MANUAL, 9800366

iv

TABLE OF CONTENTS

Chapter 1. ASSEMBLY LANGUAGE AND PROCESSORS 1-1

Introduction 1-1
What Is An Assembler? 1-1
What the Assembler Does 1-1
Oblect Code 1-2
Program Listing 1-2
Symbol-Cross-Reference Listing 1-3
Do You Need the Assembler? 1-3
Overview of 8080/8085 Hardware 1-5
Memory 1-5
ROM 1-5
RAM 1-5
Program Counter 1-6
Work Registers 1-7
Internal Work Registers 1-9
Condition Flags 1-9
Carry Flag 1-10
Sign Flag 1-10
Zero Flag 1-11
Parity Flag 1-11
Auxiliary Carry Flag 1-11
Stack and Stack Pointer 1-12
Stack Operations 1-13
Saving Program Status 1-13
Input/Output Ports . 1-14
Instruction Set 1-15
Addressing Modes 1-15
Implied Addressing 1-15
Register Addressll1g 1-15
Immediate Addressll1g 1-15
Direct Addressll1g 1-15
Register Indirect Addressing 1-16
Combined Addressing Modes 1-16
Ti mll1g Effects of Addressll1g Modes 1-16
Instruction Namll1g Conventions 1-16
Data Transfer Group 1-16
Arithmetic Group 1-17
Logical Group 1-17
Branch Group 1-18
Stack, I/O, and Machine Control Instructions 1-19
Hardware/Instruction Summary 1-19
Accumulator Instructions 1-19
Register Pair (Word) Instructions 1-21
Branching Instructions 1-22
Instruction Set Guide 1-23

v

8085 Proc ~ssor Differences 1-24
Pr )gramming for the 8085 1-24
Cc nditional Instructions 1-25

Chapter 2. ASSEMIIL Y LANGUAGE CONCEPTS 2-1

Introdu( tion 2-1
Source Line Format 2-1
Garacter Set 2-1
Delimiters 2-2
Label/Name Field 2-3
Ol'code Field 2-4
Or'erand Field 2-4
Cc mment Field 2-4
Coding Operand Field Information 2-4
He xadecimal Data 2-5
Decimal Data 2-5
O( tal Data 2-5
Bilary Data 2-5
Lc cation Counter 2-6
A~,CII Constant 2-6
Labels Assigned Values 2-6
Labels of Instruction or Data 2-6
E> pressions 2-6
In ;tructions as Operands 2-7
R( gister-Type Operands 2-7
Two's Complement Representation of Data 2-7
Symbol~ and Symbol Tables 2-9
Sy mbol ic Addressing 2-9
Sy mbolic Characteristics 2-9
Reserved, User-Defined, and Assembler-Generated Symbols 2-9
Global and Limited Symbols 2-10
Permanent and Redefinable Symbols 2-11
Absolute and Relocatable Symbols 2-11
Assembl I-Time Expression Evaluation 2-11
Or erators 2-11
Arithmetic Operators 2-12
Shift Operators 2-12
Logical Operators 2-13
Compare Operators 2-13
Byte Isolation Operators 2-14
Pe 'missible Range of Values 2-15
Pr"cedence of Operators 2-15
Rdocatable Expressions . 2-16
Cllaining of Symbol Definitions 2-18

Chapter 3. INSTRlCTION SET 3-1

How tc Use this Chapter 3-1
Timing Information 3-1
In ;tructions are listed in alphabetical order
vi

Oupter 4. ASSEMBLER DIRECTIVES 4-1

Symbol Definition 4-2
EQU Directive 4-2
SET Directive 4·3
Data Definition 4-3
DB Directive 4·3
OW Directive 44
Memory Reservuion 4-5
OS Directive 4-5
Programming Til»; D.Ha Description and Access 4-6
R.mdom Acee..s Versus ReAd Only Memory 4-6
Dua Desuiption 4-6
O.. ta Access 4-6
Add Symbols for DaLli Access 4-7
Conditional Assembly 4-8
IF, ELSE, ENDIF Directives 4-8
Assembler Termination 4-10
END Directive 4-10
Location Counter Control and Relocation 4-11
location Counter Control (Non·Rcloc.aubic Mode) 4-11
ORG Directive 4-11
Introduction to Rdocatability 4-12
Memory Management 4-12
Modular ProgrOlm Development 4-12
Directives Used for Relocation 4-14
location Counter Conlrol (Reloc<l.table Programs) 4-14
ASEG Directive 4-14
CSEG Directive 4-15
OSEG Directi"e 4-15
ORG Directive (Relocatable Mode) 4-16
Program linkage Directives 4-16
PUBLIC Directive 4-17
EXTRN Directive 4-17
NAME Directive 4-18
STKLN Directive 4-18
STACK and MEMORY Reserved Words 4-19
Programming Tips: Testing Relocatable Modules 4-19
Init~1ilation Routines 4-19
Input/Output 4-20
Remove Coding Used for Testing 4-20

Chapter S. MACROS 5·1

Introduction to Macros 5·1
Why Us.e Macros? 5-1
Wha t Is A Macro! 5-1
Macros Vs. Subroutines 5-3

vii

Lking M.cros 5-3
MUfo Definition S·)
M.cro Ddinition Directi~s S4
MACRO Directj~ S4
ENOM Oirectiw: S-5
LOCAL Oirel.livc S·S
REPT Dircllive S~
IRP Directive S·8
IRPC Directive S-8
EXITM Directive S·9
Sp«i~1 M~CfO (Jpft.ators S·IO
Nested "bero Definitions S·12
MOlCr~ DU 5·12
Muro DII fOflTWt S·12
Nested M~uo ulls S·I'
M.u..ru E).p4n,iun S·IS
Null M.cros S·16
s.ample Macros .1·16

Ch.tptt'r 6. PRCXiRAMMING TECHNIQUES 6·

Brlinch T.. oles P~udo·Subroutine 6-
lr.. mlt'rrinl DOll. [0 Subroutine . 6·)
Soflw.;ue Multiply lind Di"i~ .6·7
Multibyte Addition .nd SublrliCiion 6-11
DecirTldl Addition 6·2
Oecimal SubU,t..:tlon 6-14

Ch .. pter 7.INTERRUPTS 7·

Interrupt ConcepH 7·
Writing Interrupt Subroutint's 7·4

Ap~ndix A INSTRUCTIO SUMMARY A·
Appcndi). 8 ASSEMBLER DIRECTIVE SUMMARY B·I
Appendix C ASCII CHARACTE R SET C.I
Appendi). 0 BINARY·DECIMAL·HEXADECIMAL CONVERSION TABLES· 0·1

viii

LIST OF ILLUSTRATIONS

Figure

1-1 ASSEMBLER OUTPUTS 1-2
1-2 COMPARISON OF ASSEMBLY LANGUAGE WITH PL/M 1-4
1-3 8080{8085 INTERNAL REGISTERS 1-6
1-4 INSTRUCTION FETCH 1-8
1-5 EXECUTION OF MOV M,C INSTRUCTION 1-9

ix

1. ASSEMBLY LANGUAGE AND PROCESSORS

INTRODUCTION

Almost every line of source coding in an assembly language source program translates directly into a machine
instruction for a particular processor. Therefore, the assembly language programmer must be familiar with both
the assembly language and the processor for which he is programming. '

The first part of this chapter describes the assembler. The second part describes the features of the 8080 micro-
processor from a programmer's point of view. Programming diffel'ences between the 8080 and the 8085 micro-
processors are relatively minor. These differences are described in a short section at the end of this chapter.

WHAT IS AN ASSEMBLER?

An assembler IS a software tool - a program - deSigned to simplify the task of Writing computer programs. If
you have ever written a computer program directly in a machine-recognizable form such as binary or hexadecimal
code, you will appreciate the advantages of programming in a symbolic assembly language,

Assembly language operation codes (opcodes) are easily remembered (MOY for move instructions, JMP for jump).
You can also symbolically express addresses and values referenced in the operand field of instructions. Since you
assign these names, you can make them as meaningful as the mnemonics for the instructions. For example, if your
program nust manipulate a date as data, you can assign it the symbolic name DATE. If your program contains a
set of instructions used as a timing loop (a set of instructions executed repeatedly until a specific amount of time
has passed), you can name the instruction group TIMER.

What the Assembler Does

To use the assembler, you first need a source program. The source program consists of programmer-written
assembly language instructions. These instructions are written using mnemonic opcodes and labels as described
previously.

Assembly language source programs must be in a machine-readable form when passed to the assembler. The
Intellec development system includes a text editor that will help you maintain source programs as paper tape
files or diskette files. You can then pass the resulting source program fife to the assembler. (The text editor is
described in the ISIS-II System User's GUide.)

The assembler program performs the clerical task of translating symbolic code into ob/ect code which can be
executed by the 8080 and 8085 microprocessors. Assembler output consists of three possible files: the object
fife containing your program translated into object code; the list file printout of your source code, the assembler-
generated object code, and the symbol table; and the symbol-crass-reference file, a listing of the symbol-cross-
reference records.

1-1

Chapter 1. Assembly Lan)~uage and Processors

OBJECT

FILE

SOU<.CE ASSEMBLER PROGRAM
PROGRAM
FIl.E PROGRAM ~ LISTING

~ CROSS
REFERENCE
LISTING

Figure 1-1. Assembler Outputs

Oblect Code

For most mlcrxomputer applications, you probably will eventually load the oblect program into some form of
read only men ory, However, do not forget that the Intellec development system IS an 8080 microcomputer
system with raldom access memory, In most cases you can load and execute your oblCct program on the
development s"stem for teSlJng and debugging, TIllS allows you to test your program before your prototype
application sys:em IS fully developed,

A special featu,'e of this assembler IS that it allows you to request oblect code In a relocatable format. This frees
the programm( r from worrYing about the eventual mix of read only and random access memory In the application
system; indivicual porlJons of the program can be relocated as needed when the application design is final. Also,
a lal'ge progranl can be broken Into a number of separately assembled modules, Such modules are both easier to
code and to te;t, See Chapter 4 of this manual for a more thorough description of the advantages of the relocation
feature,

Program Listing

The program liitlng prOVides a permanent record of both the source program and the object code, The assembler
also provides diagnostic messages for common programming errors in the program listing. For example, if you
specify al6-bl value for an InstruclJon that can use only an 8-blt value, the assembler tells you that the value
exceeds the pe'missible range.

1-2

Chapter 1. Assembly Language and Processors

Symbol-Crass-Reference Listing

The symbol-crass-reference listing is another of the diagnostic tools provided by the assembler. Assume, for
example, that your program manipulates a data field named DATE, and that testing reveals a program logic
error In the handling of this data. The symbol-crass-reference listing simplifies debugging this error because it
POints you to each instruction that I"eferences the symbol DATE.

Do You Need the Assembler?

The assembler IS but one of several tools available for developing microprocessor programs. Typically, choosing
the most suitable tool IS based on cost restraints versus the required level of performance. You or your company
must determine cost restraints; the reqUired level of performance depends on a number of variables:

• The number of programs to be written: The greater the number of programs to be written, the more
you need development support. Also, It must be pOinted out that there can be penalties for not
wl"lting programs. When your application has access to the power of a microprocessor, you may be
able to provide customers with custom features through program changes. Also, you may be able to
add features through programming.

o The time allowed for programming: As the time allowed for programmll1g decreases, the need for
programmll1g support II1creases.

• The level of support for eXisting programs: Sometimes programming errors are not discovered until
the program has been 111 use for quite a while. Your need for programming support II1creases if you
agree to correct such errors for YOUI" customers. The number of supported programs In use can
multiply this requirement. Also, program support 15 frequently subrect to stringent time constraints.

If none of the factors described above apply to your Situation, you may be able to get along without the
assembler. Intel's PROMPT-80, for example, allows you to enter programs directly Into programmable read only
memory. You enter the program manually as a string of hexadeCimal digits. Such manual programming IS relatively
slow and more prone to human error than computer-assisted programmll1g. However, manual systems are one of
the least expensive tools available for mlcmprocessor programming. Manual systems may be SUitable for limited
applications, hobbyists, and those who want to explol"e possible applications for microprocessors.

If most of the factors listed preViously apply to you, you should explore the advantages of PL(M. PL/M IS
Intel's high-level language for program development. A high-level language is directed more to problem solVing
than to a particular microprocessor. TIllS allows you to write programs much more qUickly than a hardware·
oriented language such as assembly language. As an example, assume that a program must move five characters
from one location 111 memory to anothcr. Thc following cxample illustratcs the coding differences between
assembly language and PL/M. Since II1structions have not yet been described, the asscmbly language instructions
arc rcprescn ted by a flowchart.

1-3

Chapter 1. Assembly Lan 5uage and Processors

ASSEI ~BL Y LANGUAGE CODING PL/MCODING

I LOAD ,<EGISTER WITH NUMBER
OF CHARACTERS TO BE MOVED

I
I LOAD ,<EGISTER PAIR B WITH
ADDRE SS OF SOURCE (FLD1)

I
LOAD I~EGISTER PAIR D WITH
ADDRESS OF DESTINATION
(FLD2)
I

LOAD ,CCUMULATOR WITH 1
BYTE FROM SOURCE FIELD

I
MOVE :HARACTER FROM
ACCUIV ULATOR TO DESTINA-
TION FIELD

I CALL MOVE(S,FLD2,FLD1);

~
I INCREMENT SOURCE ADDRESS

I
INCRHIENT DESTINATION
ADDRESS

I
I DECRE .ENT CHARACTER COUNT

IS
NO
CHARACTER
COUNT
=O?
YES

( CONTINUE

Figure 1-2. Comparison of Assembly Language with PL/M

1-4


OVERVIEW OF 8080/8085 HARDWARE

To the programmer, the computer comprises the following parts:

• Memory
• The program cou nter
• Work registers
• Condition flags
• The stack and stack pointer
• Input/output ports
• The instruction set

Of the components listed above, memory is not part of the processor, but is of interest to the programmer.

Memory

Since the program required to drive a microprocessor resides'in memory, all microprocessor applications require
some memory. There are two general types of memory: read only memory (ROM) and random access memory
(RAM).

ROM

As the name Implies, the processor can only read instructions and data from ROM; it cannot alter the contents
of ROM. By contrast, the processor can both read from and write to RAM. Instructions and unchanging data
are permanently fixed into ROM and remain intact whether or not power is applied to the system. For this
reason, ROM is typically used for program storage in single-purpose microprocessor applications. With ROM you
can be certain that the program is ready for execution when power is applied to the system. With RAM a program
must be loaded into memory each time power is applied to the processor. Notice, however. that storing programs
in RAM allows a multi-purpose system since different programs can be loaded to serve different needs.

Two special types of ROM PROM (Programmable Read Only Memory) and EPROM (Eraseable Programmable
Read Only Memory) are frequently used during program development. These memories are useful during
program development since they can be altered by a special PROM programmer. In high-volume commercial
applications. these special memories are usually replaced by less expensive ROM's.

RAM

Even if your program resides entirely in ROM. your application is likely to require some random access memory.
Any time your program attempts to write any data to memory, that memory must be RAM. Also, if your pro-
gram uses the stack. you need RAM. If your program modifies any of its own instructions (this procedure is
discouraged), those instructions must reside in RAM.

The mix of ROM and RAM In an application IS important to both the system designer and the programmer.
Normally, the programmer must know the physical addresses of the RAM in the system so that data variables

1-5

Chapter 1. Assembly Lang Jage and Processors

can be assignee within those addresses. However, the relocation feature of this assembler allows you to code a
program witho!lt concern for the ultimate placement of data and instructions; these program elements can be
repositioned aLer the program has been tested and after the system's memory layout IS final. The relocation
feature is fully explained in Chapter 4 of this manual.

Program Counter

With the progr 1m counter, we reach the first of the 8080's Internal registers illustrated in Figure 1-3.

NOTE

Except for the differences listed at the end of this chapter,
the Information in this chapter applies equally to the 8080
and the 8085.

The program CJunter keeps track of the next instruction byte to be fetched from memory (which may be either
ROM or RAM:. Each time It fetches an instruction byte from memory, the processor increments the program
counter by on". Therefore, the program counter always indicates the next byte to be fetched. This process
continues as Ie ng as program instructions are executed sequentially. To alter the flow of program execution as
with a iump irstruction or a call to a subroutine, the processor overwrites the current contents of the program
counter with t le address of the new Instruction. The next instruction fetch occurs from the new address.

8080
IACCUMULATORI FLAGS 8085
HIGH LOW

INSTRUC~ B C STACK POINTER

DECOD::R
D E PROGRAM COUNTER

IDATA BUS_ATCH I H L ADDRESS BUS LATCH

o
8-bit
bidirecti, Inal
u
16-bit
address bus
data b JS
.--------,
ROM RAM INPUT OUTPUT
PORTS PORTS
INSTRUCTIONS INSTRUCTIONS

CONSTANT VARIABLE
DATA DATA
STACK

Figure 1-3. 8080/8085 Internal Registers

1-6


Work Registers

The 8080 provides an 8-bit accumulator and six other general purpose work registers, as shown in Figure 1-3.

Programs reference these registers by the letters A (for the accumulator), B, C, D, E, H, and L. Thus, the
Instruction ADD B may be interpreted as 'add the contents of the B register to the contents of the accumu-
lator.

Some instructions reference a pair of registers as shown in the following:

Symbolic Reference Registers Referenced

B Band C
D D and E
H Hand L
M Hand L (as a memory reference)
PSW A and condition flags (explained
later In this section)

The symbolic reference for a single register IS often the same as for a register pair. The Instruction to be executed
determines how the processor interprets the reference. For example, ADD B is an 8-blt operation. By contrast
PUSH B (which pushes the contents of the Band C registers onto the stack) is a 16-blt operation.

Notice that the letters Hand M both refer to the Hand L register pair. The choice of which to use depends on
the instruction. Use H when an instruction acts upon the Hand L register pair as In INX H (increment the
contents of Hand L by one). Use M when an instruction addresses memory via the Hand L registers as in ADD
M (add the contents of the memory location specified by the Hand L registers to the contents of the accumu-
lator).

The general purpose registers B, C, D, E, H. and L can proVide a wide variety of functions such as storing 8-bit
data values, storing intermediate results In arithmetic operations, and storing 16-bit address pointers. Because of
the 8080's extensive instruction set, it is usually possible to achieve a common result with any of several
different instructions. A Simple add to the accumulator. for example, can be accomplished by more than half a
dozen different Instructions. When possible, it is generally desirable to select a register-to-register instruction
such as ADD B. These instructions tYPically I'equire only one byte of program storage. Also, using data already
present in a register eliminates a memory access and thus reduces the time required for the operation.

The accumulator also acts as a general-purpose register, but It has some special capabilities not shared with the
other registers. For example, the Input/output instructions IN and OUT transfer data only between the accumu-
lator and external I/O deVices. Also, many operations involving the accumulator affect the condition flags as ex-
plained In the next section.

Example:

The following figures illustrate the execution of a move instruction. The MOV M.e moves a copy of the contents
of register C to the memory location specified by the Hand L registers. Notice that tillS location must be in
RAM since data is to be written to memory,

1-7

Chapter 1. Assembly Lanl uage and Processors

8080
IACCUMULATORI FLAGS
I HIGH LOW
8085
+
INSTRU(~ I B
I
e
II STACK ! POINTER
I
DECOUER
I D
I E
II PROGRAM i COUNTER

Y DATA BUS LATCH
I I H
I
L I I ADDRESS I BUS LATCH

f
L
l •
ROM RAM

Figure 1-4. Instruction Fetch

The processor initiates the instruction fetch by latching the contents of the program counter on the address bus,
and then incrEments the program counter by one to Indicate the address of the next Instruction byte. When the
memory respc nds, the Instruction is decoded into the series of actions shown in Figure 1-5.

NOTE

The following description of the execution of the
MOV M,e instruction is conceptually correct, but
does not account for normal bus control. For details
concerning memory interface, refer to the User's
Manual for your processor.

1-8


8080
8085
IACCUMULATORI FLAGS I
I B I C I HIGH LOW
INSTRUCTION
DECODER
I STACK ! POINTER
I
I D I E I I PROGRAM ! COUNTER I
DATA BUS LATCH f.- I H I L ADDRESS I BUS LATCH I

+
+ +
ROM RAM

Figure 1-5. Execution of MOY M.C Instruction

To execute the MOY M.C instruction. the processor latches the contents of the C register on the data bus and
the contents of the Hand L registers on the address bus. When the memory accepts the data, the processor
terminates execution of this instruction and initiates the next instruction fetch.

Internal Work Registers

Certain operations are destructive. For example, a compare is actually a subtract operation; a zero result indicates
that the opreands are equal. Since it is unacceptable to destroy either of the operands, the processor includes
several work registers reserved for its own use. The programmer cannot access these registers. These registers are
used for internal data transfers and for preserving operands in destructive operations.

Condition Flags

The 8080 provides five flip flops used as condition flags. Certain arithmetic and logical instructions alter one or
more of these flags to indicate the result of an operation. Your program can test the setting of four of these
flags (carry, sign. zero. and parity) using one of the conditional iump. call. or return Instructions. This allows you
to alter the flow of program execution based on the outcome of a previous operation. The fifth flag. auxiliary
carry. is reserved for the use of the DAA instruction. as will be explained later in this section.

It is important for the programmer to know which flags are set by a particular instruction. Assume, for example.
that your program is to test the parity of an input byte and then execute one instruction sequence if parity is
even. a different instruction set if parity is odd. Coding a J PE (jump if parity is even) or J PO (jump if parity is

1-9

Chapter 1. Assembly Lanfuage and Processors

odd) instructl,m Immediately foiiowing the IN (input) Instruction produces false results since the IN instruction
does not affect the condition flags. The jump executed by your program reflects the outcome of some previous
operation unrdated to the IN instruction. For the operation to work correctly, you must include some instruc-
tion that alter; the parity flag after the IN instruction, but before the lump Instruction. For example, you can
add zero to tl e accumulator. ThiS sets the parity flag without altering the data In the accumulator.

In other cases you wiii want to set a flag With one instruction, but then have a number of intervel1lng instruc-
tions before yJU use It. In these cases, you must be certain that the Intervening instructions do not affect the
desired flag.

The flags set I,y each Instruction are detailed in the IndiVidual Instruction descriptions In Chapter 3 of this
manual.

NOTE

When a flag is 'set' It IS set ON (has the value one);
when a flag IS 'reset' it IS reset OFF (has the value
zero).

Carry Flag

As ItS name it Wlies, the carry flag IS commonly used to Indicate whether an addition causes a 'carry' into the
next higher 01 del' digit. The carry flag IS also used as a 'borrow' flag In subtractions, as explallled under 'Two's
Complement :~epresentatlon of Data' In Chapter 2 of thiS manual. The carry flag is also affected by the logical
AND, OR, ani exclUSive OR Instructions. These instructions set ON or OFF particular bits of the accumulator.
See the descrJJtlons of the ANA, ANI, ORA, ORI, XRA, and XRI instructions in Chapter 3.

The rotate In'truCtions, which move the contents of the accumulator one position to the left or right, treat the
carry bit as trough it were a III nth bit of the accumulatol' See the deSCrIptions of the RAL, RAR, RLC, and RRC
instructions II' Chapter 3 of thiS manual.

Example:

Addition of ['vo one-byte numbers can produce a carry out of the high-order bit:

Bit Number: 7654 3210
AE= 1010 1110
+74= 0111 01 00

0010 001 0 = 22 carry flag = 1

An addition t lat causes a carry out of the high order bit sets the carry flag to 1, an addition that does not cause
a carry resets the flag to zero.

Sign Flag

As explained mder 'Two's Complement Representation of Data' In Chapter 2, bit 7 of a result in the accumulator
can be Interpletcd as a sign. Instructlolls that affect the sign flag set the flag equal to bit 7. A zero In bit 7

1·10


indicates a positive value; a one indicates a negative value. This value is duplicated in the sign flag so that
conditional iump, call, and return instructions can test for positive and negative values.

Zero Flag

Certain Instructions set the zero flag to one to indicate that the result in the accumulator contains all zeros.
These instructions reset the flag to zero if the result in the accumulator is other than zero. A result that has a
carry and a zero result also sets the zero bit as shown below:

1010 0111
+0101 1001

0000 0000 Carry Flag = 1
Zero Flag = 1

Parity Flag

Parity IS determined by counting the number of one bits set in the result in the accumulator. Instructions that
affect the parity flag set the flag to one for even parity and reset the flag to zero to indicate odd parity.

Auxiliary Carry Flag

The auxiliary carry flag indicates a carry out of bit 3 of the accumulator. You cannot test this flag directly in
your program; it is present to enable the DAA (Decimal Adiust Accumulator) to perform its function.

The auxiliary carry flag and the DAA instruction allow you to treat the value in the accumulator as two 4-bit
binary coded decimal numbers. Thus, the value 0001 1001 is equivalent to 19. (If this value is interpreted as a
binary number, it has the value 25.) Notice, however, that adding one to this value produces a non-decimal
result:

0001 1001
+00000001

0001 1010 = lA

The DAA instruction converts hexadecimal values such as the A in the preceding example back into binary coded
decimal (BCD) format. The DAA instruction requires the auxiliary carry flag since the BCD format makes it
possible for arithmetic operations to generate a carry from the low-order 4-bit digit Into the high-order 4-bit
digit. The DAA performs the following addition to correct the preceding example:

0001 1010
+00000110

0001 0000
+0001 0000 (auxiliary carry)

0010 0000 = 20

1-11

Chapter 1. AssemblY Lan5uage and Processors

The auxiliary carry flag is affected by all add, subtract, increment, decrement, compare, and all logical AND,
OR, and excl Jsive OR instructions. (See the descriptions of these Instructions In Chapter 3.) There is some
difference in the handling of the auxiliary carry flag by the logical AND instructions In the 8080 processor and
the 8085 pro ;essor. The 8085 logical AND instructions always set the auxiliary flag ON. The 8080 logical AND
instructions s,t the flag to reflect the logical OR of bit 3 of the values involved in the AND operation.

Stack and Stack Po inter

To understan j the purpose and effectiveness of the stack, it is useful to understand the concept of a subroutine.

Assume that !our program requires a multiplication routine. (Sinoe the 8080 has no multiply instruotions, this
oan be performed through repetitive addition. For example, 3x4 is equivalent to 3+3+3+3.) Assume further that
your progralT needs this multiply routine several times. You can recode this routine inline each time it is needed,
but this can lise a great deal of memory. Or, you can code a subroutine:

nline Coding Subroutine

1
nline routine
1
CALL

I
nline routine
I
CALL . subroutine

I
nline routine
I
CALL

I I
The 8080 provides instruotions that call and return from a subroutine. When the call instruction is executed, the
address of th, next instruction (the contents of the program counter) IS pushed onto the stack. The contents of
the program :ounter are replaced by the address of the desired subroutine. At the end of the subroutine, a
return instruction pops that previously-stored address off the stack and puts it back into the program counter.
Program exe( ution then continues as though the subroutine had been coded inline.

The mechani;m that makes this possible IS, of course, the staok. The stack is simply an area of random access
memory addi essed by the stack pointer. The stack pointer IS a hardware register maintained by the processor.
However, YOiJr program must initialize the stack pointer. This means that your program must load the base
address of the stack into the stack pointer. The base address of the stack is commonly assigned to the highest
available add'ess in RAM. This is because the stack expands by decrementing the stack pointer. As items are

1-12


added to the stack. it expands into memory locations with lower addresses. As Items are removed from the
stack. the stack pointer is incremented back toward Its base address. Nonetheless. the most recent item on the
stack is known as the 'top of the stack.' Stack is still a most descriptive term because you can always put
something else on top of the stack. In terms of programming, a subroutine can call a subroutine, and so on.
The only limitation to the number of items that can be added to the stack is the amount of RAM available for
the stack.

The amount of RAM allocated to the stack is important to the programmer. As you write your program. you
must be certain that the stack will not expand into areas reserved for other data. For most applications. this
means that you must assign data that requires RAM to the lowest RAM addresses available. To be more precise.
you must count up all instructions that add data to the stack. Ultimately, your program should remove from
the stack any data it places on the stack. Therefore. for any IIlstruction that adds to the stack. you can sub-
tract any intervening instruction that removes an Item from the stack. The most critical factor is the maximum
size of the stack. Notice that you must be sure to remove data your program adds to the stack. Otherwise, any
left-over items on the stack may cause the stack to grow into portions of RAM you intend for other data.

Stack Operations

Stack operations transfer sixteen bits of data between memory and a pair of processor registers. The two basIc
operations are PUSH. which adds data to the stack. and POP, which removes data from the stack.

A call Instruction pushes the contents of the program counter (which contains the address of the next instruction)
onto the stack and then transfers control to the desired subroutine by placing its address in the program counter.
A return instruction pops sixteen bits off the stack and places them in the program counter. This requires the
programmer to keep track of what is in the stack. For example. if you call a subroutine and the subroutine
pushes data onto the stack, the subroutine must remove that data before executing a return instruction. Other-
wise, the return IIlstructlon pops data from the stack and places It in the program counter. The results are
unpredictable, of course. but probably not what you want.

Savll7g Program Status

It is likely that a subroutine requires the use of one or more of the working registers. However, it IS equally
likely that the main program has data stored in the registers that it needs when control returns to the main
program. As general rule, a subroutine should save the contents of a register before using it and then restore
the contents of that register before returning control to the main program. The subroutine can do this by
pushing the contents of the registers onto the stack and then popping the data back into the registers before
executing a return. The following instruction sequence saves and restores all the working registers. Notice that
the POP instructions must be in the opposite order of the PUSH instructions if the data is to be restored to its
original location.

1-13

Chapter 1. Assembly langJage and Processors

SUBRTN: PUSH PSW
PUSH B
PUSH o
PUSH H

subroutine coding

POP H
POP 0
POP B
POP PSW
RETURN

The letters B, 0, and H refer to the Band C, 0 and E, and Hand L register pairs, respectively, PSW refers to
the program s atus word. The program status wOl'd IS a 16-blt word comprising the contents of the accumulator
and the five c,jnpitlon flags. (PUSH PSW adds three bits of filler to expand the condition flags into a full
byte; POP PSII strrps out these filler bits.)

Input/Output Ports

The 256 rnpul/output ports provide communication with the outside world of perrpheral devices. The IN and
OUT instructl<lns initiate data transfers.

The IN rnstrw tion latches the number of the desired port onto the address bus. As 500n as a byte of data 15

returned to the data bus latch, it is transferred into the accumulator.

The OUT inst: uetion latches the number of the desired port onto the address bus and latches the data in the
accumulator onto the data bus.

The specified )ort number 15 duplicated on the address bus. Thus, the instruction IN 5 latches the bit configura-
tion 0000 01 (1 0000 0101 onto the address bus.

Notice that the IN and OUT instructions Simply Initiate a data transfer It is the responsibility of the peripheral
device to dete~t that It has been addressed. Notice also that it is possible to dedicate any number of ports to
the same perr, hera I device. You might use a number of ports as control signals, for example.

Because input and output are almost totally application dependent, a discussion of design techniques IS beyond
the scope of t liS manual.

For additional hardware Information. refer to the 8080 or 8085 Microcomputer Systems User's Manual.

For related prJgrammlng rnformation, see the descriptions of the IN, OUT, 01, EI, RST, and RIM and SIM
Instructions In Chapter 3 of this manual. (The RIM and SIM instructions apply only to the 8085.)

1-14


Instruction Set

The 8080 incorporates a powerful array of Instructions. This section provides a general overview of the Instruc-
tion set. The detailed operation of each instruction is described In Chapter 3 of tillS manual.

Addressing Modes

Instructions can be categorized according to their method of addressing the hardware registers and/or memory.

Implied AddresslI1g. The addressing mode of certain Instructions is implied by the instruction's function. For
example, the STC (set carry flag) instruction deals only with the carry flag; the DAA (decimal adjust accumu-
lator) instruction deals with the accumulator.

Register AddresslI1g. QUite a large set of instructions call for register addressing. With these instructions, you
must specify one of the registers A through E, H or L as well as the operation code. With these instructions,
the accumulator IS implied as a second operand. For example, the instruction CMP E may be Interpreted as
'compare the contents of the E register with the contents of the accumulator.'

Most of the Instructions that use register addressing deal with 8-bit values. However, a few of these Instructions
deal with 16-bit register pairs. For example, the PCHL Instruction exchanges the contents of the program counter
with the contents of the Hand L registers.

Immediate AddresslI1g. Instructions that use Immediate addressing have data assembled as a part of the instruction
Itself. For example, the Instruction CPI 'C' may be Interpreted as 'compare the contents of the accumulator with
the letter c.' When assembled, this instruction has the hexadecimal value FE43. Hexadecimal 43 IS the Internal
representation for the letter C. When this instruction IS executed, the processor fetches the first instruction byte
and determines that it must fetch one more byte. The processor fetches the next byte Into one of its internal
registers and then performs the compare operation.

Notice that the names of the Immediate instructions indicate that they use immediate data. Thus, the name of an
add instruction is ADD; the name of an add Immediate Instruction is AD!.

All but two of the Immediate instructions use the accumulator as an Implied operand, as in the CPI instruction
shown previously The MV! (move Immediate) Instruction can move its immediate data to any of the working
registers, including the accumulator, or to memory. Thus, the Instruction MVI D,OFFH moves the hexadecimal
value FF to the D register.

The LXI Instruction (load register pair immediate) is even more unusual in that ItS Immediate data IS a 16-bit
value. This instruction is commonly used to load addresses Into a register pair. As mentioned previously, YOUl'
program must initialize the stack pointer; LXI IS the instruction most commonly used for this purpose. For ex-
ample, the instruction LXI SP,30FFH loads the stack pointer with the hexadecimal value 30FF

Direct AddresslI1g. Jump Instructions include al6-bit address as part of the instruction. For example, the
Instruction J MP 1000H causes a jump to the hexadecimal address 1000 by replacing the current contents of the
program counter with the new value 1000.

1-15

Chapter 1. Assemblv Lang Jage and Processors

Instructions that include a direct address require three bytes of storage: one for the Instruction code. and two
for the 16-bit lddress.

Register IndirEct Addressing. Register indirect instructions reference memory via a register pair. Thus, the
Instruction MC>V M,C moves the contents of the C register into the memory address stored in the Hand L
register pair. 1 he instruction LDAX B loads the accumulator with the byte of data specified by the address
In the Band C register pair.

Combmed Ad,lressmg Modes. Some instructions use a combination of addressing modes. A CALL instruction,
for example, combines direct addressing and register Indirect addressing. The direct address in a CALL instruction
specifies the address of the deSIred subroutine; the register indirect address IS the stack pointer. The CALL
instruction pu,hes the current contents of the program counter into the memory location specified by the stack
pointer

Timmg Effect~ of Addressmg Modes. Addressing modes affect both the amount of time required for executing
an Instruction and the amount of memory reqUired for ItS storage. For example, instructions that use implied or
register addres;ing execute very qUickly since they deal directly with the processor hardware or with data already
present in hardware I·egisters. More important, however, is that the entire instruction can be fetched with a
single memory access. The number of memory accesses required is the single greatest factor in determining
execution timing. More memory accesses require more execution time. A CALL instruction, for example, requires
five memory accesses: three to access the entire Instruction, and two more to push the contents of the program
counter onto ',he stack.

The processor can access memory once during each processor cycle. Each cycle comprises a variable number of
states. (The Injividual instruction descriptions in Chapter 3 specify the number of cycles and states required for
each Instructic n.) The length of a state depends on the clock frequency specified for your system, and may
range from 48) nanoseconds to 2 microseconds. Thus, the timing of a four state instruction may range from
1.920 microse:onds through 8 microseconds. (The 8085 has a maximum clock frequency of 320 nanoseconds
and therefore :an execute instructions about 50% faster than the 8080.)

Instruction Nam/ilg Conventions

The mnemonl<s assigned to the instructions are designed to indicate the function of the instruction. The Instruc·
tions fall into the following functional categories:

Data Tral1Sfer Group. The data transfer instructions move data between registers or between memory and
registers.

MOV Move
MVI Move Immediate
LDA Load Accumulator Directly from Memory
STA Store Accumulator Directly in Memory
LHLD Load Hand L Registers Directly from Memory
SHLD Store Hand L Registers Directly in Memory

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1-16


An 'X' In the name of a data transfer instruction implies that it deals with a register pair:

LXI Load Register Pair with Immediate data
LDAX Load Accumulator from Address in Register Pair
STAX Store Accumulator in Address in Register Pair
XCHG Exchange Hand L with D and E
XTHL Exchange Top of Stack with Hand L

Arithmetic Group. The arithmetic instructions add, subtract, increment, or decrement data in registers or
memory.

ADD Add to Accumulator
ADI Add Immediate Data to Accumulator
ADC Add to Accumulator Using Carry Flag
ACI Add Immediate Data to Accumulator Using Carry Flag
SUB Subtract from Accumulator
SUI Subtract Immediate Data from Accumulator
SBB Subtract from Accumulator Using Borrow (Carry) Flag
SBI Subtract Immediate from Accumulator Using Borrow
INR Increment Specified Byte by One
DCR Decrement Specified Byte by One
INX Increment Register Pair by One
DCX Decrement Register Pair by One
DAD Double Register Add: Add Contents of Register
Pair to Hand L Register Pair

Logical Group. This group performs logical (Boolean) operations on data in registers and memory and on
condition flags.

The logical, AND, OR, and Exclusive OR instructions enable you to set specific bits in the accumulator ON or
OFF.

ANA Logical AND with Accumulator
ANI Logical AND with Accumulator Using Immediate Data
ORA Logical OR with Accumulator
ORI Logical OR with Accumulator Using Immediate Data
XRA Exclusive Logical OR with Accumulator
XRI Exclusive OR Using Immediate Data

The compare instructions compare the contents of an 8·blt value with the contents of the accumulator:

CMP Compare
CPI Compare Using Immediate Data

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'-17

Chapter 1. Assembly Lang1lage and Processors

The rotate instructions shift the contents of the accumulator one bit position to the left or right:

RLC Rotate Accumulator Left
RRC Rotate Accumulator Right
RAL Rotate Left Through Carry
RAR Rotate Right Through Carry

Complement ald carry flag instructions:

CMA Complement Accumulator
CMC Complement Carry Flag
STC Set Carry Flag

Branch Group. The branching instructions alter normal sequential program flow. either unconditionally or
conditionallY. fhe unconditional branching instructions are as follows:

jMP Jump
CALL Call
RET Return

Conditional bnnching Instructions examine the status of one of four condition flags to determine whether the
specified brant h IS to be executed. The conditions that may be specified are as follows:

NZ Not Zero (Z = 0)
Z Zero (Z = 1)
NC No Carry (C = 0)
C Carry (C = 1)
PO Parity Odd (P = 0)
PE Parity Even (P = 1)
P Plus (5 = 0)
M Minus (5 1)

Thus. the conditional branching Instructions are specified as follows:

Jumps Calls Returns

jC CC RC (Carry)
jNC CNC RNC (No Carry)
jZ CZ RZ (Zero)
jNZ CNZ RNZ (Not Zero)
jP CP RP (Plus)
jM CM RM (Minus)
jPE CPE RPE (Parity Even)
jPO CPO RPO (Parity Odd)

Two other instructions can effect a branch by replacing the contents of the program counter:

PCHL Move Hand L to Program Counter
RST Special Restart Instruction Used with Interrupts
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1-18


Stack, //0, and Machine Contra/Instructions. The following instructions affect the stack and/or stack pOinter'

PUSH Push Two Bytes of Data onto the Stack
POP Pop Two Bytes of Data off the Stack
XTHL Exchange Top of Stack with Hand L
SPHL Move contents of Hand L to Stack Pointer

The I/O instructions are as follows:

IN Initiate Input Operation
OUT Initiate Output Operation

The machine control Instructions are as follows:

EI Enable Interrupt System
DI Disable Interrupt System
HLT Halt
NOP No Opel'ation

HARDWARE/INSTRUCTION SUMMARY

The following illustrations graphically summarize the instruction set by showing the hardware acted upon by
specific instructions, The type of operand allowed for each Instruction IS Indicated through the use of a code,
When no code is given. the Instruction does not allow operands.

Code Meaning

REGM S The opel'and may specify one of the S-bit registers A,B.C,D,E,H, or L or M
(a memory reference via the 16-blt address in the Hand L registers). The
MOV Instruction. which calls for two operands, can specify M for only one
of its operands.
Designates S-bit immediate operand.
Designates a 16-bit address.
Designates an S-bit port number
Designates a 16-blt register pair (B&C,D&E,H&L, or SP).
Designates a 16-blt immediate operand,

Accumulator Instructions

The following illustration shows the Instructions that can affect the accumulator, The instructions listed above
the accumulator all act on the data in the accumulator, and all except CMA (complement accumulator) affect
one or more of the condition flags. The instructions listed below the accumulator move data Into or out of the
accumulator, but do not affect condition flags. The STC (set carry) and CMC (complement carry) instructions
are also shown hel'e,

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1-19

Chapter 1. Assembly Lan ,uage and Processors

ADD ADI
ADC ACI
SUB SUI
SBB SBI
ANA REGM S D
ANI S
XRA XRI
ORA ORI
CMP CPI
RLC RAL RRC
RAR CMA DAA
INR}

,-1
REGM
DCR S

ACCUMULATORI FLAGS
I STC CMC
HIGH LOW

I I B I_ _
C
---lI STACK POINTER

MOV REGM S: REC Msi D I E
J I PROGRAM COUNTER I

J~
L
I
HI
LDAX} MEMORY
STAX EC,DE

LDA I
STA} 1'16

MVI [J STACK
S
MOV F.EGMS,REG
S


1·20


Register Pair (Word) Instructions

The following instructions all deal with 16-bit words. Except for DAD (which adds thecontents of the B&C or
D&E register pair to H&L), none of these instructions affect the condition flags. DAD affects only the carry
flag.

IACCUMULATORI FLAGS
INX} HIGH LOW
B C DCX
DAD
REG
16 fSPH' -I STACK ! POINTER

.- D E
I"""xcHG
PCHL _I PROGRAM! COUNTER I
..",..-
H L

XTHL

LHLD
SHLD

I
MEMORY

STACK PUSH }
POP B,D,H,PSW


1-21

Chapter 1. Assembly Lalguage and Processors

Branching Instructions

The followin~ Instructions can alter the contents of the program counter, thereby altering the normal sequential
execution flew. Jump instructions affect only the program counter. Call and Return Instructions affect the
program coullter, stack pointer, and stacK.

~CUMjLATORI FLAGS
I HIGH LOW

~i C
I POINTER

~) E I I PCHL COUNTER RST

~I L
~
JMP CALL RET

JC
JZ
JNC 1
JNZ (> A
CC
CZ
CNC}
CNZ A
RC
RZ
RNcl
RNZ A
IP 1M I 16 CP CM 16 RP RM J> 16
JPE JPO J CPE CPO RPE RPO

MEMORY CONTROL INSTRUCTIONS

RST
Nap
HLT
EI
01
STACK
SIM} 8085 only
RIM

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1-22

Chapter 1. Assembly language and Processors

Instruction Set Guide

The following is a summary of the instruction set:
ADI
ADDl
ADC ACI
SUB SUI
SBB REGM S SBI DS
ANA ANI
XRA XRI
ORA ORI
CMP CPI

RLC RAL RRC
RAR CMA DAA
INR}
DCR REGM S

"ACCUMULATORI FLAGS ISTC CMC HIGH LOW
MOY REGMS,REGM S ! B I C
INX}
IDCX REG 16 STACK , POINT;ER

1
LXI REG 16 ,D 16
I D I E ~XCHG
RST
H L

jMP CALL RET
jC CC CNCl RC RNCi
jNC1
jZ jNZ A CZ CNZ A RZ RNZ ~ A
jP jM 16 J CP CM J16 RP RM J 16
jPE jPO CPE CPO RPE RPO

LHLD}
STHD A16 OUT P
~ s CONTROL
LDAX BC DE
STAX) , INSTRUCTIONS
INPUT OUTPUT
MEMORY
PORTS PORTS RST
NOP
HLT
EI
MYI DS DI
MOY REGMS,REGM S
--STAC"K--- ~- :~~H} B,D,H,PSW SIMI
SOS5 ONLY
RIM]
CODE MEANING

REGM S The operand may specify one of the S-bit registers A,B,C,D,E,H, or l or M (a memory
reference via the 16-bit address in the Hand L registers). The MOY instruction, which
calls for two operands, can specify M for only one of its operands.
Designates S-bit immediate operand.
Designates a 16-bit address.
Designates an S-bit port number.
Designates a '16-bit register pair (B&C,D&E,H& L,or SP).
Designates a 16 -bit immediate operand.

1-23

Chapter 1. Assemblv Lalguage and Processors

8085 PROCESSOR DIFFERENCES

The differences between the 8080 processor and the 8085 processor will be more obvious to the system designer
than to the programmer. Except for two additional instructions. the 8085 i"~truction set is identical to and fully
compatible with the 8080 instruction set. Most programs written for the 8680 should operate on the 8085 with-
out modifica1ion. The only programs that may require changes are those with critical timing routines; the higher
system speed of the 8085 may alter the time values of such routines.

A partial listing of 8085 design features Includes the following:

• A single 5 volt power supply.
• Execution speeds approximately 50% faster than the 8080.
• Incorporation in the processor of the features of the 8224 Clock Generator and Driver and the
8228 System Controller and Bus Driver.
• A non-maskable TRAP interrupt for handling serious problems such as power failures.
• Three separately maskable interrupts that generate internal RST instructions.
• Input/output lines for serial data transfer

Programming for tile 8085

For the prog ·ammer. the new features of the 8085 are summarized In the two new Instructions SIM and RIM.
These instructions differ from the 8080 instructions in that each has multiple functions. The SIM instruction
sets the interrupt mask and/or writes out a bit of serial data. The programmer must place the deSIred interrupt
mask and/or serial output In the accumulator prior to execution of the SIM instruction. The RIM Instruction
reads a bit 0 serial data if one is present and the Interrupt mask Into the accumulator. Details of these instruc-
tions are cov"red in Chapter 3.

Despite the Ilew Interrupt features of the 8085. programming for interrupts is little changed. Notice, however, that
8085 hardware interrupt RESTART addresses fall between the eXisting 8080 RESTART addresses. Therefore.
only four bytes are available for certain RST instructions. Also, the TRAP interrupt Input is non-maskable and
cannot be di ;abled. If your application uses this input, be certain to provide an interrupt routine for it.

The interrup:s have the following priority:

TRAP highest
RSn.5
RST6.5
RST5.5
INTR lowest

When more han one interrupt is pending, the processor always recognizes the higher priority Interrupt first.
These priorii ies apply only to the sequence in which interrupts are recognized. Program routines that service
interrupts h,ve no special priority. Thus. an RST5.5 interrupt can Interrupt the service routine for an RST7.5
interrupt. If you want to protect a service routine from interruption, either disable the interrupt system (01
instruction), or mask out other potential interrupts (SIM instruction).

1-24


Conditional Instructions

Execution of conditional instructions on the 8085 differs from the 8080. The 8080 fetches all three instruction
bytes whether or not the condition is satisfied. The 8085 evaluates the condition while it fetches the second
instruction byte. If the specified condition is not satisfied, the 8085 skips over the third instruction byte and
immediately fetches the next Instruction. Skipping the unnecessary byte allows for faster execution.

1-25

2. ASSEMBLY LANGUAGE CONCEPTS

INTRODUCTION

Just as the English languagc has its [-ulcs of grammar, assembly language has certalll coding rules. The source line
[5the assembly language equivalent of a sentencc.

Th[s assembler recognizcs three types of source lines: IIlstruct[ons, directives, and controls. This manual describes
instructions and dircctlves. Controls are dcscribed [n the operator's manual for your version of the assembler.

Th[s chapter dcscribes thc general rules for coding sourcc lincs. Specific instructions (see Chapter 3) and
directives (see Chapters 4 and 5) may have specific coding rules. Even 50, the coding of such Instructions and
directives must conform to thc gencral rules in this chapter.

SOURCE LINE FORMAT

Assembly language [nstructlons and asscmblcr directives may consist of up to four fields, as follows:

Label:) Opcodc Operand ;Comment
{ Name

Thc fields may be separated by any numbe[- of blanks, but must be separated by at least one delimlter_ Each
IIlstruction and directive must be entered on a single line term lila ted by a carriage return and a line fced. No
continuation lines are possiblc, but you may havc lines conSisting enti[-ely of commcnts.

Character Set

The following characters are Icgal In asscmbly languagc source statements:

• Thc lctters of the alphabet, A through Z. Both upper- and lower-case letters are allowed. Internally,
the assemblc[- trcats all letters as though they wcre upper-casc, but the characters are printed exactly
as they were Input in the assembly listing.

• The digits 0 through 9.

• The following speCial characters:

2-1

Chapter 2. Assembly Lan luage Concepts

Character Meaning

+ Plus sign
Minus sign
* Asterisk
Slash
Comma
Left parenthesis
Right parenthesis
Single quote
& Ampersand
Colon
$ Dollar sign
@ Commercial 'at' sign
Question mark
Equal sign
< Less than sign
> Greater than sign
% Percent sign
Exclamation point
blank Blank or space
Semicolon
Period
CR Carnage return
FF Form feed
HT Horizontal tab

.. In addition, any ASCII character may appear in a string enclosed In single quotes or in a comment.

Delimiters

Certain chara<:ters have special meaning to the assembler in that they function as delimiters. Delimiters define
the end of a ,ource statement, a field, or a component of a field. The following list defines the delimiters
recognized by the assembler, Notice that many delimiters are related to the macro feature explained In Chapter
5. Delimiters Jsed for macros are shown here so that you will not accidentally use a delimiter improperly
Refer to Chal,ter 5 for a description of macros.

2-2

Chapter 2. Assembly Language Concepts

Charaeter(s) Meaning Use

blank one or more field separator or symbol terminator
blanks

comma separate operands in the operands field,
including macro parameters

pair of single delimit a character string
quote characters

(..• J pair of paren- delimit an expression
theses

CR carriage return statement terminator

HT horizontal tab field separator or symbol terminator

semicolon comment field delimiter

colon delimiter for symbols used as labels

& ampersand delimit macro prototype text or formal
parameters for concatenation

<... > pair of angle delimit macro parameter text which
brackets contains commas or embedded blanks;
also used to delimit a parameter list

% percent sign delimit a macro parameter that is to be
evaluated prior to substitution

exclamation an escape character used to pass the
point following character as part of a macro
parameter when the character might
otherwise be interpreted as a delimiter

double semi- delimiter for comments in macro definitions
colon when the comment is to be suppressed when
the macro is expanded

Label/Name Field

Labels are always optional. An instruction label is a symbol name whose value is the location where the instruc-
tion is assembled. A label may contain from one to SIX alphanumeric characters, but the first character must be
alphabetic or the special characters '7' or '@' The label name must be terminated with a colon. A symbol used
as a label can be defined only once in your program. (See 'Symbols and Symbol Tables' later in this chapter.)

2-3

Chapter 2. Assemblv Lallguage Concepts

Alphanumerit: characters include the letters of the alphabet, the question mark character, and the decimal
digits 0 throl gh 9.

A name is required for the SET. EQU, and MACRO directives. Names follow the same coding rules as labels,
except that t ley must be terminated with a blank rather than a colon. The label/name field must be empty for
the LOCAL ind ENDM directives.

Opcode Field

This required field contains the mnemonic operation code for the 8080/8085 instruction or assembler directive
to be perforned.

Operand Field

The operand field identifies the data to be operated on by the specified opcode. Some instructions require no
operands. Otners require one or two operands. As a general rule, when two operands are required (as in data
transfer and lrithmetic operations), the first operand identifies the destination (or target) of the operation's
result, and tlie second operand specifies the source data.

Examples:

MOil A,C ;MOVE CONTENTS OF REG C TO ACCUMULATOR
MV A:B' ;MOVE B TO ACCUMULATOR

Comment Field

The optiona comment field may contain any information you deem useful for annotating your program. The
only coding requirement for this field is that it be preceded by a semicolon. Because the semicolon is a delimiter,
there IS no reed to separate the comment from the previous field with one or more spaces. However, spaces are
commonly Lsed to improve the readability of the comment. Although comments are always optional, you should
use them lib;rally since it is easier to debug and maintain a well documented program.

CODING OPERAI~D FIELD INFORMATION

There are feur types of information (a through d in the following list) that may be requested as items in the
operand field; the information may be specified in nine ways, each of which is described below.

2-4

Chapter 2. Assembly language Concepts

OPERAND FIELD INFORMATION

Information reqUIred Ways of specitying

(a) Register (1) Hexadecimal Data
(b) Register Pair (2) Decimal Data
(c) Immediate Data (3) Octal Data
(d) 16-bit Address (4) Binary Data
(5) Location Counter ($)
(6) ASCII Constant
(7) Labels assigned values
(8) Labels of instructions or data
(9) Expressions

Hexadecimal Data. Each hexadecimal number must begin with a numeric digit (0 through 9) and must be
followed by the letter H.

Label Opcode Operand Comment

HERE: MVI C,OBAH ;LOAD REG C WITH HEX BA

DecImal Data. Each decimal number may be identified by the letter D immediately after its last digit or may
stand alone. Any number not specifically identified as hexadecimal, octal, or binary is assumed to be decimal.
Thus. the following statements are equivalent:


ABC: MVI E,15 ;LOAD E WITH 15 DECIMAL
MVI E,15D

Octal Data. Each octal number must be followed by the letter 0 or the letter Q.


LABEL: MVI A,nQ ;LOAD OCTAL 72 INTO ACCUM

Binary Data. Each binary number must be followed by the letter B.


NOW: MVI D,l1l1 011 OB ;LOAD REGISTER D
;WITH OF6H

2-5

Chapter 2. Assemblv L, nguage Concepts

Location Counter, The $ character refers to the current location counter. The location counter contains the
address wher~ the current instruction or data statement will be assembled.

label Opcode Operand Comment

co: jMP $+6 ;j UMP TO ADDRESS 6 BYTES BEYOND
;THE FIRST BYTE OF THIS
;INSTRUCTION

ASCII Const1t7t. One or more ASCII characters enclosed in single quotes define an ASCII constant. Two
successive sillgle quotes must be used to represent one slllgie quote Within an ASCII constant.

i.abel Opcode Operand Comment

MYI E '*' ;LOAD E REG WITH 8-BIT ASCII
;REPRESENTATION OF *
DATE: DB TODAY"S DATE'

Labels Assig led Values. The SET and EQU directives can assign values to labels. In the following example,
assume that VALUE has been assigned the value 9FH; the two statements are equivalent:

Opcode Operand Comment

1. MYI D,9FH
2: MYI D,YALUE

Labels of In;truction or Data. The label assigned to an IIlstructlon or a data definition has as its value the
address of tile first byte of the instruction or data. Instructions elsewhere in the program can refer to this
address by I:S symbolic label name.

Opcode Operand Comments

-jERE: jMP THERE ;jUMP TO INSTRUCTION AT THERE

fHERE; MVI D,9FH

Expressions. All of the operand types discussed previously can be combined by operators to form an expression.
In fact, the example given for the location counter ($+6) IS an expression that combines the location counter
with the decimal number 6.

Because the rules for coding expressions are rather extensive, further discussion of expressions is deferred until
later in this chapter.

2-6


Instructions as Operands. One operand type was intentionally omitted from the list of operand field infor-
mation: Instructions enclosed in parentheses may appear in the operands field. The operand has the value of
the left-most byte of the assembled instruction.

Label Opcode Operand

INS: DB (ADD C)

The statement above defines a byte with the value 81 H (the object code for an ADD C instruction). Such
coding is typically used where the object program modifies itself during execution, a technique that is strongly
discouraged.

Register-Type Operands. Only instructions that allow registers as operands may have register-type operands.
Expressions containing register-type operands are flagged as errors. Thus, an instruction like

JMP A

is flagged as an illegal use of a register.

The only assembler directives that may contain register-type operands are EQU, SET, and actual parameters in
macro calls. Registers can be assigned alternate names only by EQU or SET.

TWO'S COMPLEMENT REPRESENTATION OF DATA

Any 8-bit byte contains one of the 256 possible combinations of zeros and ones. Any particular combination may
be interpreted in a number of ways. For example, the code 1 FH may be interpreted as an instruction (Rotate
Accumuiator Right Through Carry), as the hexadecimal value 1 F, the decimal value 31, or simply the bit
pattern 00011111.

Arithmetic instructions assume that the data bytes upon which they operate are in the 'two's complement'
format. To understand why, let us first examine two examples of decimal arithmetic:

35 35
-12 +88

23 123

Notice that the results of the two examples are equal if we disregard the carry out of the high order position in
the second example. The second example illustrates subtraction performed by adding the ten's complement of
the subtrahend (the bottom number) to the minuend (the top number). To form the ten's complement of a
decimal number, first subtract each digit of the subtrahend from 9 to form the nine's complement; then add one
to the result to form the ten's complement. Thus, 99-12=87; 87+1=88, the ten's complement of 12.

The ability to perform subtraction with a form of addition is a great advantage in a computer since fewer cir-
cuits are required. Also, arithmetic operations within the computer are binary, which simplifies matters even more.

2-7

Chapter 2. Assembly Lalguage Concepts

The processol forms the two's complement of a binary value simply by reversing the value of each bit and then
adding one tc the result. Any carry out of the high order bit is ignored when the complement is formed. Thus,
the subtractic n shown previously is performed as follows:

35 = 001 0 0011 00100011
-12 = 0000 1100 = 1111 0011 +11110100

23 + 1 0001 0111 = 23

1111 01 00

Again, by dis 'egarding the carry out of the high order position, the subtraction IS performed through a form of
addition. HO/ever, if this operation were performed by the 8080 or [he 8085, the carry flag would be set OFF
at the end of the subtraction. This is because the processors complement the carry flag at the end of a subtract
operation so :hat it can be used as a 'borrow' flag in multibyte subtractions. In the example shown, no borrow
IS reqUired. St> the carry flag IS set OFF. By contrast, the carry flag IS set ON if we subtract 35 from 12:

12 = 000011 00 00001100
-35 = 0010 0011 = 11 01 11 00 +1101 1101

+
-----'-
1110 1001 = 233 or --105

1101 1101

In this case, he absence of a carry indicates that a borrow IS reqUired from the next higher order byte, if any
Therefore, th 0 processor sets the carry flag ON. Notice also that the result is stored In a complemented form.
If you want 0 Interpret this result as a deCimal value, you must again form its two's complement:

111 0 1001 = 0001 011 0
+ 1

0001 0111 = 23

Two's compl·'ment numbers may also be signed. When a byte IS Interpreted as a signed two's complement number,
the high ordu bit indicates the sign. A zero In thiS bit indicates a positive number, a one a negative number. The
seven low order bits provide the magnitude of the number. Thus, 0111 1111 equals +127

At the beglnlling of this description of two's complement arithmetic, it was stated that any 8-blt byte may con-
tain one of tile 256 possible combinations of zeros and ones. It must also be stated that the proper interpretation
of data is a r r,ogramming responsibility.

As an examp,e, consider the compare instruction. The compare logiC considers only the raw bit values of the
Items being compared. Therefore, a negative two's complement number always compares higher than a positive
number, bec;use the negative number's high order bit IS always ON. As a result, the meanings of the flags set by
the compare instruction are reversed. Your program must account for this condition.

2-8


SYMBOLS AND SYMBOL TABLES

Symbolic Addressing

If you have never done symbolic programming before, the following analogy may help clarify the distinction
between a symbolic and an absolute address.

The locations in program memory can be compared to a cluster of post office boxes. Suppose Richard Roe
rents box 500 for two months. He can then ask for his letters by saying 'Give me the mail in box 500: or
'Give me the mail for Roe.' If Donald Smith later rents box 500, he too can ask for his mail by either box
number 500 or by his name. The content of the post office box can be accessed by a fixed. absolute address
(500) or by a symbolic. variable name. The postal clerk correlates the symbolic names and their absolute values
In hiS log book. The assembler performs the same function. keeping track of symbols and their values in a
symbol table. Note that you do not have to assign values to symbolic addresses. The assembler references its
location counter during the assembly process to calculate these addresses for you. (The location counter does
for the assembler what the program counter does for the microcomputer. It tells the assembler where the next
instruction or operand is to be placed in memory.)

Symbol Characteristics

A symbol can contain one to six alphabetic (A-Z) or numeric (0-9) characters (with the first character alphabetic)
or the special character '7' or '@'. A dollar sign can be used as a symbol to denote the value currently in the
location counter For example, the command

jMP $+6

forces a jump to the instruction residing six memory locations higher than the JMP instruction. Symbols of the
form '??nnn' are generated by the assembler to uniquely name symbols local to macros.

The assembler regards symbols as haVing the following attributes: reserved or user-defined; global or limited;
permanent or redefinable; and absolute or relocatable.

Reserved. User-Defined. and Assembler-Generated Symbols

Reserved symbols are those that already have special meaning to the assembler and therefore cannot appear as
user-defined symbols. The mnemonic names for machine instructions and the assembler directives are all reserved
symbols.

2-9

Chapter 2. Assembly Lan;:uage Concepts

The following instruction operand symbols are also reserved:

Symbol Meaning

$ Location counter reference
A Accumulator register
B Register B or register pair Band C
C Register C
D Register D or register pair D and E
E Register E
H Register H or register pair Hand L
L Register L
SP Stack pointer register
PSW Program status word (Contents of A and status flags)
M Memory reference code using address in Hand L
STACK Special relocatability feature
MEMORY Special relocatability feature

NOTE

The STACK and MEMORY symbols are fully discussed
in Chapter 4.

User-defined' ymbols are symbols you create to reference Instruction and data addresses. These symbols are
defined when they appear in the label field of an instruction or In the name field of EQU, SET, or MACRO
directives (see Chapters 4 and 5).

Assembler-ger erated symbols are created by the assembler to replace user-defined symbols whose scope is limited
to a macro d, finition.

Global and Um/'ed Symbols

Most symbol, are global. This means that they have meaning throughout your program. Assume, for example,
that you assifn the symbolic name RTN to a routine. You may then code a iump or a calJ to RTN from any
POlllt in your program. If you assign the symbolic name RTN to a second routine, an error results since you
have given ml i1tiple definitions to the same name.

Certain symbJls have meaning only within a macro definition or within a calJ to that macro; these symbols are
'local' to the macro. Macros require local symbols because the same macro may be used many times in the
program. If tile symbolic names within macros were global, each use of the macro (except the first) would cause
multiple defililtlons for those symbolic names.

See Chapter .; for additional information about macros.

2·10


Permanent and Redefinable Symbols

Most symbols are permanent since their value cannot change during the assembly operation. Only symbols
defined with the SET and MACRO assembler directives are redefinable.

Absolute and Relocatable Symbols

An important attribute of symbols with this assembler is that of relocatability. Relocatable programs are
assembled relative to memory location zero. These programs are later relocated to some other set of memory
locations. Symbols with addresses that change dUring relocation are relocatable symbols. Symbols with
addl-esses that do not change during relocation are absolute symbols. This distinction becomes important when
the symbols are used within expressions, as will be explained later.

External and public symbols are special types of relocatable symbols. These symbols are required to establish
program linkage when several relocatable program modules are bound together to form a single application
program. External symbols are those used in the current program module, but defined In another module.
Such symbols must appear in an EXTRN statement, or the assembler will flag them as undefined.

Conversely, PUBLIC symbols are defined in the current program module, but may be accessed by other
modules. The addresses for these symbols are resolved when the modules are bound together.

Absolute and relocatable symbols may both appear in a relocatable module. References to any of the assembler-
defined registers A through E, Hand L, PSW, SP, and M are absolute since they refer to hardware locations.
But these references are valid in any module.

ASSEMBLY-TIME EXPRESSION EVALUATION

An expression IS a combination of numbers, symbols, and operators. Each element of an expression is a term.

Expressions, like symbols, may be absolute or relocatable. For the sake of readers who do not require the
relocation feature, absolute expressions are described first. However, users of relocation should read all the
following.

Operators

The assembler Includes five groups of operators which permit the following assembly-time operations: arithmetic
operations, shift operations, logical operations, compare operations, and byte Isolation operations. It is important
to keep in mind that these are all assembly-time operations. Once the assembler has evaluated an expression, it
becomes a permanent part of your program. Assume, for example, that your program defines a list of ten con-
stants starting at the label LIST; the following instruction loads the address of the seventh item in the list Into
the Hand L registers:

LXI H,L1ST+6

Notice that LIST addresses the first item, L1ST+l the second, and so on.

2-11

Chapter 2. Assembly Lan ~uage Concepts

Arithmetic Open tors

The anthmeti, operators are as follows:

Operator Meaf7/1lg

+ Unary or binary addition
Unary or blllary subtraction
* Multiplication
Division. Any remainder is discarded (7/2=3).
Division by zero causes an error.
MOD Modulo. Result is the remainder caused by a
division operation. (7 MOD 3=1)

Examples:

The follOWing expressions generate the bit pattern for the ASCII character A;

5+30*2
(25/5)+30*2
5+( -30*·2)

Notice that tLe MOD operdtor must be separdted from ItS operands by spaces:

NUMBR MOD 8

Assuming tha. NUMBR has the value 25, the previous expression evaluates to the value

Shift Operators

The shift ope'atars are as !"ollows:

Operator Meol7lf7g

y SHR x Shift operand 'y' to the nght 'x' bit posItions.

y SHL x Shift operand 'y' to the le!"t 'x' bit positions.

The shift operators do not wraparound any bits shihed out of the byte. Bit positions vacated by the shift
operation are zero·filled. Notice that the shift operatar must be separated from ItS operands by spaces.

Example:

Assume that NUMBR has the value 0101 0101, The effects of the shift operators is as follows:

NUMBR SHR 0001 0101

NUMBR SHL 1010 1010

2-12


Notice that a shift one bit position to the left has the effect of multiplying a value by two; a shift one bit
position to the right has the effect of dividing a value by two.

Logical Operators

The logical operators are as follows;

Operator Meaning

NOT Logical one's complement

AND Logical AND (=1 if both ANDed bits are 1)

OR Logical OR (=1 if either ORed bit is 1)

XOR Logical EXCLUSIVE OR (=1 if bits are different)

The logical operators act only upon the least significant bit of values involved in the operation. Also, these
operators are commonly used In conditional IF directives. These directives are fully explained in Chapter 4.

Example:

The following IF directive tests the least significant bit of three Items. The assembly language code that follows
the IF is assembled only if the condition IS TRUE. This means that all three fields must have a one bit in the
least significant bit position.

IF FLDI AND FLD2 AND FLD3

Compare Operators

The compare operators are as follows:

Operator Meaning

EQ Equal
NE Not equal
LT Less than
LE Less than or equal
GT Greater than
GE Greater than or equal
NUL Special operator used to test for null (missing) macro
parameters

2-13

Chapter 2. Assembly Lan ;uage Concepts

The compare )perators Yield a yes-no result. Thus. if the evaluation of the relation is TRUE. the value of the
result is all ores. If false. the value of the result is all zeros. Relational operations are based strictly on magni-
tude comparisons of bit values. Thus. a two's complement negative number (which always has a one in its high
order bit) is g'eater than a two's complement positive number (which always has a zero in its high order bit).

Since the NU'_ operator applies only to the macro feature, NUL is described in Chapter 5.

The compare operators are commonly used in conditional IF directives. These directives are fully explained in
Chapter 4.

Notice that tl,e compare operator must be separated from its operands by spaces.

Example:

The following IF directive tests the values of FLDl and FLD2 for equality. If the result of the comparison is
TRUE, the aSiembly language coding following the IF directive IS assembled. Otherwise. the code is skipped over.

IF FLDl EQ FLD2

Byte Isolation Ooerators

The byte isolltion operators are as follows:

Operator Meaning

HIGH Isolate hlgh·order 8 bits of 16-bit value

LOW Isolate low-order 8 bits of 16-blt value.

The assemble- treats expressions as 16-blt addresses. In certain cases. you need to deal only with a part of an
address. or Y<lU need to generate an 8-bit value. This IS the function of the HIGH and LOW operators.

The assembler's relocation feature treats all external and relocatable symbols as 16-bit addresses. When one of
these symbol; appears in the operand expression of an Immediate instruction. It must be preceded by either the
HIGH or LON operator to specify which byte of the address IS to be used In the evaluation of the expression.
When neithel operator is present. the assembler assumes the LOW operator and Issues an error message.

NOTE

Any program segment containing a symbol used as the
argument of a HIGH operator should be located only on
a page boundary. This is done using the PAGE option
with the CSEG or DSEG directives described in Chapter
4. Carries are not propagated from the low-order byte
when the assembler object code is relocated and the
carry flag will be lost. Using PAGE ensures that this
flag is 0_
2-14


Examples:

Assume that ADRS is an address manipulated at assembly-time for building tables or lists of items that must all
be below address 255 in memory. The following IF directive determines whether the high-order byte of ADRS
is zero, thus indicating that the address is still less than 256:

IF HIGH ADRS EQ 0

Permissible Range of Values

Internally, the assembler treats each term of an expression as a two-byte, 16-bit value. Thus, the maximum
range of values is OH through OFFFFH. All arithmetic operations are performed using unsigned two's comple-
ment arithmetic. The assembler performs no overflow detection for two-byte values, so these values are evaluated
modulo 64K.

Certain Instructions require that their operands be an eight-bit value. Expressions for these instructions must
yield values in the range -256 through +255. The assembler generates an error message if an expression for one
of these instructions yields an out-of-range value.

NOTE

Only instructions that allow registers as operands may have
register-type operands. Expressions containing register-type
operands are flagged as errors. The only assembler directives
that may contain register-type operands are EQU, SET, and
actual parameters in macro calls. Registers can be assigned
alternate names only by EQU or SET.

Precedence of Operators

Expressions are evaluated left to right. Operators with higher precedence are evaluated before other operators
that immediately precede or follow them. When two operators have equal precedence, the left-most is evaluated
first.

Parentheses can be used to override normal rules of precedence. The part of an expression enclosed In paren-
theses is evaluated first. If parentheses are nested, the Innermost are evaluated first.

15/3 + 18/9 =5+2=7
15/(3 + 18/9) = 15/(3 + 2) = 15/5 = 3

2-15

Chapter 2. Assembly Lan :uage Concepts

The following list describes the classes of operators in order of precedence:

• Parenthesized expressions
• NUL
• HIGH, LOW
• Multiplication/Division: *. /, MOD, SHL, SHR
• Addition{Subtraction: +, - (unary and binary)
Relational Operators: EQ, LT, LE, GT, GE, NE
• Logical NOT
• Logical AND
• Logical OR, XOR
The relational, logical, and HIGH{LOW operators must be separated from their operands by at least one blank.

Relocatable Express ions

Determining t le relocatability of an expression requires that you understand the relocatability of each term used
in the express on. This is easier than it sounds since the number of allowable operators is substantially reduced.
But first it is lecessary to know what determines whether a symbol is absolute or relocatable.

Absolute symJols can be defined two ways:

• A symbol that appears in a label field when the ASEG directive is in effect IS an absolute symbol.
• A symbol defined as equivalent to an absolute expression using the SET or EQU directive is an
absolute symbol.

Relocatable s"mbols can be defined a number of ways:

• A symbol that appears in a label field when the DSEG or CSEG directive IS in effect is a relocatable
symbol.
• A symbol defined as equivalent to a relocatable expression using the SET or EQU directive is
reocatable.
• Tile special assembler symbols STACK and MEMORY are relocatable.
• E,ternal symbols are considered relocatable.
• A reference to the location counter (specified by the $ character) IS relocatable when the CSEG or
o ,EG directive is in effect.
The expressions shown in the following list are the only expressions that yield a relocatable result. Assume that
ABS IS an ab~olute symbol and RELOC IS a relocatable symbol:

ABS + RELOC
RELOC + ABS
RELOC - ABS
fHIGH'( RELOC+ABS
LOW )
[ HIGH ~ RELOC _ ABS
~LOW )
r
HIGH}
RELOC + ~ LOW ABS
f HIGH '1
RELOC LOW } ABS

2-16

Chapter 2. Assemblv Language Concepts

Remember that numbers are absolute terms. Thus the expression RELOC - 100 is legal, but 100 - RELOC
is not.

When two relocatable symbols have both been defined with the same type of relocatability, they may appear In
certain expressions that yield an absolute result. Symbols have the same type of relocatability when both are
relative to the CSEG location counter, both are relative to the DSEG location counter, both are relative to
MEMORY, or both are relative to STACK. The following expressions are val id and produce absolute results:

RELOCl - RELOC2
EQ
LT
RELOCl LE RELOC2
GT
GE
NE

Relocatable symbols may not appear In expressions with any other operators.

The following list shows all possible combinations of operators with absolute and relocatable terms. An A in the
table indicates that the resulting address is absolute: an R indicates a relocatable address; an I Indicates an
illegal combination. Notice that only one term may appear with the last five operators in the list.

X absolute X absolute X relocatable X relocatable
Operator
Y absolute Y relocatable Y absolute Y reloca table

X + Y A R R I
X Y A I R A
X * y A I I I
X / y A I I I
X MOD y A I I I
X SHL Y A I I I
X SHR Y A I I I
X EQ Y A I I A
X LT Y A I I A
X LE Y A I I A
X GT Y A I I A
X GE Y A I I A
X NE Y A I I A
X AND y A I I I
X OR y A I I I
X XOR Y A I I I
NOT X A - I
HIGH X A - R -
LOW X A - R -
unary+ X A - R -
unary- X A - I

2-17

Chapter 2. Assemblv Larguage Concepts

Chaining of Symbol Definitions

The ISIS-II 81180/808S Macro Assembler is essentially a 2-pass assembler. All symbol table entries must be
resolvable in ; wo passes. Therefore,

x EQU y
y EQU 1

is legal, but iii the series

x EQU y
y EQU Z
Z EQU 1

the first line s illegal as X cannot be resolved in two passes and remains undefined.

2-18

3. INSTRUCTION SET

HOW TO USE THIS CHAPTER

This chapter is a dictionary of 8080 and 8085 Instructions. The instruction descriptions are listed alphabetically
for quick reference. Each description is complete so that you are seldom required to look elsewhere for addition-
al information.

This reference format necessarily requires repetitive information. If you are reading this manual to learn about
the 8080 or the 8085, do not try to read this chapter from ACI (add immediate with Carry) to XTHL (exchange
top of stack with Hand L registers). Instead, read the description of the processor and instruction set in
Chapter 1 and the programming examples in Chapter 6. When you begin to have questions about particular
instructions, look them up in this chapter.

TIMING INFORMATION

The instruction descriptions in this manual do not explicitly state execution timings. This is because the basic
operating speed of your processor depends on the clock frequency used in your system.

The 'state' IS the basic unit of time measurement for the processor. A state may range from 480 nanoseconds
(Cl20 nanoseconds on the 8085) to 2 microseconds, depending on the clock frequency. When you know the
length of a state In your system. you can determine an instruction's basic execution time by multiplying that
figure by the number of states required for the instruction.

Notice that two sets of cycle/state specifications are given for 8085 conditional call and jump instructions. This
is because the 8085 fetches the third instruction byte only if it is actually needed; i.e., the specified condition
is satisfied.

This basic timing factor can be affected by the operating speed of the memory in your system. With a fast
clock cycle and a slow memory, the processor can outrun the memory. In this case, the processor must wait
for the memory to deliver the desired instruction or data. In applications with critical timing requirements, this
wait can be significant. Refer to the appropriate manufacturer's literature for memory timing data.

3·1

Chapter 3. Instruction Se·

ACI ADD IMMEDIATE WITH CARRY

ACI adds the :ontents of the second instruction byte and the carry bit to the contents of the accumulator and
stores the result in the accumulator,

Opcode Operand

ACI data

The operand SJecifies the actual data to be added to the accumulator except, of course, for the carry bit. Data
may be in the form of a number, an ASCII constant, the label of a previously defined value, or an expression.
The data may not exceed one byte.

The assemblers relocation feature treats all external and relocatable symbols as 16-bit addresses. When one of
these symbols appears in the operand expression of an immediate instruction, It must be preceded by either the
HIGH or LOA operator to specify which byte of the address is to be used in the evaluation of the expression.
When neither )perator is present, the assembler assumes the LOW operator and issues an error message.

o 0 o
data

Cycles: 2
States: 7
AddreSSing: Immediate
Flags: Z,S,P,CY,AC

Example:

Assume that the accumulator contains the value 14H and that the carry bit is set to one. The instruction ACI 66
has the follol' ing effect:

Accumulator = 14H 00010100
Immediate data = 42H 01000010
Carry 1
01010111 57H

ADC ADD WITH CARRY

The ADC inst ruction adds one byte of data plus the setting of the carry flag to the contents of the accumulator.
The result istored in the accumulator ADC then updates the setting of the carry flag to indicate the outcome
of the operaton.

The ADC innuction's use of the carry bit enables the program to add multi-byte numeric strings.

3-2

Chapter 3. Instruction Set

Add RegIster to Accumulator with Carry

Opccde Operand

ADC reg

The operand must specify one of the registers A through E, H or L. This instruction adds the contents of the
specified register and the carry bit to the accumulator and stores the result in the accumulator.

',-1_ _ _ 0_ _1 S
0_0 _ S S I
CYcles: 1
States: 4
Addressings: register
Flags: Z.s,P,CY,AC

Add Memory to Accumulator with Carry

Opcode Operand

ADC M

This instruction adds the contents of the memory location addressed by the Hand L registers and the carry
bit to the accumulator and stores the result in the accumulator. M is a symbolic reference to the Hand L
registers.

CYcles: 2
States: 7
AddreSSing: register indirect
Flags: Z,S,P,CY,AC

Example:

Assume that register C contains 3DH, the accumulator contains 42H, and the carry bit is set to zero. The
instruction ADC C performs the addition as follows:

3DH 00111101
42H 01000010
CARRY o
01111111 = 7 FH

The condition flags are set as follows:

Carry 0
Sign 0
Zero 0
ParitY 0
Aux. Carry 0

3-3


If the carry !>it IS set to one, the instruction has the following results:

3DH 00111101
42H 01000010
CARRY 1
10000000 SOH

Carry o
Sign 1
Zero o
ParitY o
Aux, Carry 1

ADD ADD

The ADD In,truction adds one byte of data to the contents of the accumulatoL The result is stored in the
accumulator Notice that the ADD instruction excludes the carry flag from the addition but sets the flag to
indicate the Jutcome of the operation.

Add Regtstet to Register

Opcode Operand

ADD reg

The operand must specify one of the registers A through E, H or L. The instruction adds the contents of the
specified reg ster to the contents of the accumulator and stores the result in the accumulator.

11 0 0 0 0 Iss sl
Cycles: 1
States: 4
Addressing: register
Flags: Z,S,P,CY,AC

Add From Memory

Opcode Operand

ADD M

This InstruCilon adds the contents of the memory location addressed by the Hand L registers to the contents of
the accumulltor and stores the result in the accumulator. M is a symbolic reference to the Hand L registers.

11 0 0 0 0

Cycles: 2
States: 7
Addressing: register Indirect
Flags: Z,S,P,CY,AC
34


Examples:

Assume that the accumulator contains 6CH and register D contains 2EH. The Instruction ADD D performs the
addition as follows:

2EH 0010111 0
6CH 011011 00

9AH 10011010

The accumulator contains the value 9AH following execution of the ADD D instruction. The contents of the D
register remain unchanged. The condition flags are set as follows:

Carry 0
Sign 1
Zero 0
Parity 1
Aux. Carry 1

The following instruction doubles the contents of the accumulator:

ADD A

ADI ADD IMMEDIATE

ADI adds the contents of the second instruction byte of the contents of the accumulator and stores the result
in the accumulator.

Opcode Operand

ADI data

The operand specifies the actual data to be added to the accumulator This data may be In the form of a number,
an ASCII constant, the label of a previously defined value, or an expression. The data may not exceed one byte.

these symbols appears in the operand expression of an immediate instruction, it must be preceded by either
the HIGH or LOW operator to specify which byte of the address is to be used In the evaluation of the expression.
When neither operator is present. the assembler assumes the LOW operator and Issues an error message.

' 000

lCycles:
data

2
States: 7
Addressing: immediate
Flags: Z.S.P.CY,AC

3-5

Chapter 3. Instruction Se

Example:

Assume that he accumulator contains the value 14H. The Instruction ADI 66 has the following effect:

Accumulator 14H 00010100
Immediate data 42H 01000010
01010110 = 56H

Notice that ti,e assembler converts the decimal value 66 into the hexadecimal value 42.

ANA LOGICAL AND WITH ACCUMULATOR

ANA perforrrs a logical AND operation using the contents of the specified byte and the accumulator, The result
IS placed in tlie accumulator.

SummGlY of ~oglcal Operations

AN D product s a one bit In the result only when the corresponding bits In the test data and the mask data are
ones.

OR produces a one bit In the result when the corresponding bits in either the test data or the mask data are
ones.

Exclusive OR produces a one bit only when the corresponding bits in the test data and the mask data are
different; I.e. a one bit in either the test data or the mask data - but not both - produces a one bit In the
result.

AND OR EXCLUSIVE OR

1010 1010 1010 1010 1010 1010
0000 1111 0000 1111 0000 1111
0000 1010 1010 1111 1010 0101

AND Registe, with Accumulator

Opcode Operand

ANA reg

The operand must specify one of the registers A through E, H or L. ThiS instruction ANDs the contents of the
specified regi iter with the accumulator and stores the result in the accumulator, The carry flag is reset to zero.

I,-~_O O_O_I S S S I
Cycles: 1
States: 4
Flags: Z,S,P,CY,AC

3-6


AND Memory with Accumulator

Opcode Operand

ANA M

This Instruction ANDs the contents of the specified memory location with the accumulator and stores the result
in the accumulator. The carry flag is reset to zero.

o o 0

Cycles: 2
States: 7
Flags: Z,S,P,CY.AC

Example:

Since any bit ANDed with a zero produces a zero and any bit ANDed with a one remains unchanged, AND is
frequently used to zero particular groups of bits. The following example ensures that the high-order four bits of
the accumulator are zero, and the low·order four bits are unchanged. Assume that the C register contains OFH:

Accumulator 1 1 1 1 o 0 OFCH
C Register o000 1 1 OFH
000 0 o 0 OCH

ANI AND IMMEDIATE WITH ACCUMULATOR

ANI performs a logical AND operation using the contents of the second byte of the Instruction and the accumu-
lator. The result is placed In the accumulator. AN I also resets the carry flag to zero.

Opcode Operand

ANI data

The operand must specify the data to be used In the AND operation. This data may be in the form of a number,
an ASCII constant, the label of some previously defined value, or an expression. The data may not exceed one
byte.

these symbols appears in the operand expression of an immediate instruction, it must be preceded by either the
HIGH or LOW operator to specify which byte of the address is to be used in the evaluation of the expression.
When neither operator is present, the assembler assumes the LOW operator and issues an error message.

3-7

Chapter 3. Instruction Se:

' o 0

l data

Cycles: 2
States: 7
Flags: Z.S.P.CY,AC

Summary of ~oglcal Operations

AND prodUCt s a one bit in the result only when the corresponding bits In the test data and the mask data are
ones.

OR produces a one bit in the result when the corresponding bits In either the test data or the mask data are
ones.

different; i.e. a one bit in either the test data or the mask data - but not both - produces a one bit in the
result.

AND OR EXCLUSIVE OR

1010 1010 1010 1010 1010 1010
0000 1111 0000 1111 0000 1111
00001010 1010 1111 1010 0101

Example:

The followin;. instruction IS used to reset OFF bit SIX of the byte In the accumulator:

ANI 1011111IB

Since any bit ANDed with a one remains unchanged and a bit ANDed with a zero is rest to zero, the ANI
instruction srown above sets bit six OFF and leaves the others unchanged. This technique IS useful when a
program uses individual bits as status flags.

CALL CALL

The CALL Irstructlon combines functions of the PUSH and I MP Instructions. CALL pushes the contents of the
program coullter (the address of the next sequential instruction) onto the stack and then iumps to the address
specified in t le CALL instruction.

Each CALL Instruction or one of ItS variants implies the use of a subsequent RET (return) Instruction. When a
call has no cllrresponding return. excess addresses are built up in the stack.

3-8


Opcode Operand

CALL address

The address may be specified as a number, a label, or an expression. (The label is most common.) The assembler
inverts the high and low address bytes when it assembles the instruction.

1 1 0 0 1 1 0 1

low addr

high addr

Cycles: 5
States: 17 (18 on 8085)
Addressing: immediate/register indirect
Flags: none

Example:

When a given coding sequence is required several times in a program, you can usually conserve memory by coding
the sequence as a subroutine invoked by the CALL instruction or one of its variants. For example, assume that
an application drives a six-digit LED display; the display is updated as a result of an operator input or because
of two different calculations that occur in the program. The coding required to drive the display can be included
in-line at each of the three points where it is needed, or it can be coded as a subroutine. If the label DISPL Y is
assigned to the first instruction of the display driver, the following CALL instruction is used to invoke the
display subroutine:

CALL DISPLY

This CALL instruction pushes the address of the next program instruction onto the stack and then transfers
control to the DISPLY subroutine. The DISPLY subroutine must execute a return instruction or one of its
variants to resume normal program flow. The following is a graphic illustration of the effect of CALL and return
instructions:

CALL
_ ~ DISPLY
---
CALL ~ DISPL Y - - - - -
------- ---
- --
RET
CALL DISPL Y

Consideration for Using Subroutines

The larger the code segment to be repeated and the greater the number of repetitions, the greater the potential
memory savings of using a subroutine. Thus, if the display driver in the previous example requires one hundred

3-9


bytes, coding it In-line would require three hundred bytes. Coded as a subroutine, it requires one hundred bytes
plus nine bytls for the three CALL instructions.

Notice that slJbroutines require the use of the stack. This requires the application to include random access
memory for 1 he stack. When an application has no other need for random access memory, the system designer
might elect to) avoid the use of subroutines.

CC CALL IF CARRY

The CC instnlction combines functions of the JC and PUSH instructions. CC tests the setting of the carry flag.
If the flag is ,et to one, CC pushes the contents of the program counter onto the stack and then jumps to the
address sped"ied in bytes two and three of the CC instruction. If the flag is reset to zero, program execution
continues whh the next sequential instruction.

Opcode Operand

CC address

Although thE use of a label is most common, the address may also be specified as a number or expression.

1 1 0 1 1 1 0 0

lowaddr

high addr

Cycles: 3 or 5 (2 or 5 on 8085)
States: 11 or 17 (9 or 18 on 8085)
AddreSSing: immediate/register indirect
Flags: none

Example:

For the sake of brevity, an example IS given for the CALL instruction but not for each of its closely related
variants.

CM CALL IF MINUS

The CM inst-uction combines functions of the J M and PUSH instructions. CM tests the setting of the sign flag.
If the flag is set to one (indicating that the contents of the accumulator are minus), CM pushes the contents
of the progr,lm counter onto the stack and then jumps to the address specified by the CM instruction. If the
flag is set to zero, program execution simply continues with the next sequential instruction.

Opcode Operand

CM address

3-10


Although the use of a label is most common, the address may also be specified as a number or an expression.

1 1 1 1 1 1 0 0

lowaddr

high addr

Cycles: 3 or 5 (2 or 5 on 8085)
States: 11 or 17 (9 or 18 on 8085)
Flags: none

Example:

For the sake of brevity, an example is given for the CALL instruction but not for each of ItS closely related
variants.

CMA COMPLEMENT ACCUMULATOR

CMA complements each bit of the accumulator to produce the one's complement. All condition flags remain
unchanged.

Opcode Operand

CMA

Operands are not permitted with the CMA instruction.

10 0 o
Cycles: 1
States: 4
Flags: none

To produce the two's complement, add one to the contents of the accumulator after the CMA instructions has
been executed.

Example:

Assume that the accumulator contains the value 51H; when complemented by CMA, it becomes OAEH:

51H 01010001
OAEH 10101110

3-11

Chapter 3. Instruction S, t

CMC COMPLEMENT CARRY

If the carry flag equals zero, CMC sets it to one. If the carry flag is one, CMC resets it to zero. All other flags
remain unch,nged.

Opcode Operand

CMC

Operands are not permitted with the CMC instruction.

10 0
Cycles: 1
States: 4
Flags: CYonly

Example:

Assume that a program uses bit 7 of a byte to control whether a subroutine is called. To test the bit, the pro-
gram loads ti,e byte into the accumulator, rotates bit 7 into the carry flag, and executes a CC (Call if Carry)
instruction. l:efore returning to the calling program, the subroutine reinitializes the flag byte using the following
code:

CMC ;SET BIT 7 OFF
RAR ;ROTATE BIT 7 INTO ACCUMULATOR
RET ;RETURN

CMP COMPARE WITH ACCUMULATOR

CMP compar,s the specified byte with the contents of the accumulator and Indicates the result by setting the
carry and zelo flags. The values being compared remain unchanged.

The zero flal indicates equality. No carry indicates that the accumulator is greater than the specified byte; a
carry indicaus that the accumulator IS less than the byte. However, the meaning of the carry flag is reversed
when the values have different signs or one of the values is complemented.

The program tests the condition flags using one of the conditional Jump, Call, or Return instructions. For
example, J Z (J ump if Zero l tests for equality

Functnnal Description:

Comparisons are performed by subtracting the specified byte from the contents of the accumulator, which
IS why the zero and carry flags indicate the result. This subtraction uses the processor's internal registers
so that source data is preserved. Because subtraction uses two's complement addition, the CMP instruction
recoml'lements the carry flag generated by the sUbtraction.

3-12


Compare Register with Accumulator

Opcode Operand

CMP reg

The operand must name one of the registers A through E, H or L.

S s sl
Cycles: 1
States: 4
Flags: Z,S,P,CY,AC

Compare Memory with Accumulator

Opcode Operand

CMP M

This instruction compares the contents of the memory location addressed by the Hand L registers with the
contents of the accumulator. M is a symbolic reference to the Hand L register pair.

Cycles: 2
States: 7
Addressing: register indirect
Flags: Z,S,P,CY,AC

Example 1:

Assume that the accumulator contains the value OAH and register E contains the value OSH. The instruction
CMP E performs the following internal subtraction (remember that subtraction is actually two's complement
addition):

Accumulator 00001010
+( -E Register) 11111011
00000101 +(-carry)

After the carry is complemented to account for the subtract operation, both the zero and carry bits are zero,
thus indicating A greater than E.

Example 2:

Assume that the accumulator contains the value -1 BH and register E contains OSH:

+(-E Register) 11111011
111 00000 +(-carry)
3-13

Chapter 3. Instruction S ,t

After the 01P Instruction recomplements the carry flag, both the carry flag and zero flag are zero. Normally
this indicate, that the accumulator is greater than register E. However. the meaning of the carry flag IS reversed
since the val Jes have different signs. The user program is responsible for proper interpretation of the carry flag.

CNC CALL IF NO CARRY

The CNC in, truction combines functions of the JNC and PUSH instructions. CNC tests the setting of the carry
flag. If the fag is set to zero, CNC pushes the contents of the program counter onto the stack and theniumps
to the addre;s specified by the CNC instruction. If the flag IS set to one, program execution simply continues
with the ne> t sequential instruction.

Opcode Operand

CNC address

Although th,: use of a label is most common, the address may also be specified as a number or an expression.

1 1 0 1 0 1 0 0

low addr

high addr

Cycles: 3 or 5 (2 or 5 on 8085)
States: 11 or 17 (9 or 18 on 8085)
Addressing: immediate/register Indirect
Flags: none

Example:

vanants.

CNZ CALL IF NOT ZERO

The CNZ In, tructlon combines functions of the J NZ and PUSH Instructions. CNZ tests the setting of the zero
flag. If the fag is off (indicating that the contents of the accumulator are other than zero), CNZ pushes the
contents of :he program counter onto the stack and then jumps to the address specified in the Instruction's
second and hiI'd bytes. If the flag is set to one, program execution simply continues with the next sequential
instruction.

Opcode Operand

CNZ address

Although th; use of a label is most common, the address may also be specified as a number or an expression.

3-14


1 1 0 0 0 1 0 0

lowaddr

high addr

Cycles: 3 or 5 (2 or 5 on 8085)
States: 1.1 or 17 (9 or 18 on 8085)
Flags: none

Example:

For the sake of breVity, an example is given for the CALL instruction but not for each of its closely related
variants.

CP CALL IF POSITIVE

The CP instruction combines features of the J P and PUSH instructions. CP tests the setting of the sign flag. If
the flag is set to zero (indicating that the contents of the accumulator are positive). CP pushes the contents of
the program counter onto the stack and theniumps to the address specified by the CP Instruction. If the flag
is set to one, program execution simply continues with the next sequential instruction.

Opcode Operand

CP address

Although the use of a label is more common, the address may also be specified as a number or an expression.

1 1 1 1 0 1 0 0

low address

high addr

Cycles: 3 or 5 (2 or 5 on 8085)
States: 11 or 17 (9 or 18 on 8085)
Flags: none

Example:

For the sake of brevity, an example is given for the CALL instruction but not for each of its closely related
variants.

3-15

Chapter 3. Instruction Se,

CPE CALL IF PARITY EVEN

Parity is even if the byte in the accumulator has an even number of one bits. The parity flag is set to one to
indicate this condition. The CPE and CPO instructions are useful for testing the parity of input data. However,
the IN instruc tion does not set any of the condition flags. The flags can be set without altering the data by
adding OOH t" the contents of the accumulator.

The ePE instI uction combines functions of the JPE and PUSH instructions. CPE tess the setting of the parity
flag. If the flog is set to one, CPE pushes the contents of the program counter onto the stack and then jumps
to the addres' specified by the CPE instruction. If the flag is set to zero, program execution simply continues
with the next sequential instruction.

Opcode Operand

CPE address


1 1 1 0 1 1 0 0

lowaddr

high addr

Cycles: 3 or 5 (2 or 5 on 8085)
States: 11 or 17 (9 or 18 on 8085)
Addressing: immediate/register Indirect
Flags: none

Example:

For the sake )f brevity, an example is given for the CALL instruction but not for each of its closely related
variants.

CPI COMPARE IMMEDIATE

CPI compare, the contents of the second instruction byte with the contents of the accumulator and sets the zero
and carry flap to indicate the result. The values being compared remain unchanged.

The zero flag Indicates equality. No carry indicates that the contents of the accumulator are greater than the
immediate da :a; a carry Indicates that the accumulator is less than the immediate data. However, the meaning
of the carry 1lag is reversed when the values have different signs or one of the values is complemented.

Opcode Operand

CPI data

3·16


The operand must specify the data to be compared. This data may be in the form of a number, an ASCII
constant, the label of a previously defined value, or an expression. The data may not exceed one byte.

these symbols appears in the operand expression of an immediate instruction, it must be preceded by either
the HIGH or LOW operator to specify which byte of the address is to be used In the evaluation of the
expression. When neither operator is present, the assembler assumes the LOW operator and issues an error
message.

o
data

Cycles: 2
States: 7
Flags: Z,S,P,CY,AC

Example:

The instruction CPI 'C' compares the contents of the accumulator to the letter C (43H).

CPO CALL IF PARITY ODD

Parity is odd if the byte in the accumulator has an odd number of one bits. The panty flag is set to zero to
indicate this condition. The CPO and CPE instructions are useful for testing the parity of input data. However,
the IN instruction does not set any of the condition flags. The flags can be set without altering the data by
adding OOH to the contents of the accumulator.

The CPO instruction combines functions of the JPO and PUSH instructions. CPO tests the setting of the panty
flag. If the flag is set to zero, CPO pushes the contents of the program counter onto the stack and then jumps
to the address specified by the CPO instruction. If the flag is set to one, program execution simply continues

Opcode Operand

CPO address


1 1 1 0 0 1 0 0

lowaddr

high addr

Cycles: 3 or 5 (2 or 5 on 8085)
States: 11 or 17 (9 or 18 on 8085)
Flags: none
3-17

Chapter 3. Instruction Sf t

Example:

For the sake of brevity, an example is given for the CALL Instruction but not for each of its closely related
vanants.

CZ CALL IF ZERO

The CZ instrJCtion combines functions of the I Z and PUSH Instructions. CZ tests the setting of the zero flag.
If the flag IS ;et to one (indicating that the contents of the accumulator are zero), CZ pushes the contents of
the program :ounter onto the stack and then lumps to the address specified in the CZ instruction. If the flag
IS set to zero (indicating that the contents of the accumulator are other than zero), program execution simply
continues wil h the next sequential Instruction.

Opcode Operand

CZ address

Although the use of a label is most common, the address may also be specified as a number or an expression.

1 I 0 0 1 1 0 0

lowaddr

high addr

Cycles: 3 or 5 (2 or 5 on 8085)
States: 11 or 17 (9 or 18 on 8085)
Addressing: Immediate/register Indirect
Flags: none

Example:

vanants.

DAA DECIMAL ADJUST ACCUMULATOR

The DAA lIl~truction adjusts the eight-bit value in the accumulator to form two four-bit binary coded deCimal
digits.

Opcode Operand

DAA

Operands are not permitted with the DAA IIlstructlon.

DAA IS used when adding deCimal numbers. It is the only instruction whose function requires use of the auxiliary
carry flag. In multi-byte arithmetiC operations, the DAA instruction typically is coded immediately after the arith-
metic instruc tion so that the auxiliary carry flag is not altered unintentionally.

3-18


DAA operates as follows:

1. If the least significant four bits of the accumulator have a value greater than nine, or if the auxiliary
carry flag is ON, DAA adds six to the accumulator.

2. If the most significant four bits of the accumulator have a value greater than nine, or if the carry
flag IS ON, DAA adds six to the most significant four bits of the accumulator.

10 0 o 0

Cycles: 1
States: 4
Flags: Z,S,P,CY,AC

Example:

Assume that the accumulator contains the value 9BH as a result of adding 08 to 93:

CY AC
0 0

1001 0011
0000 1000
1001 1011 = 9BH

Since OBH IS greater than nine, the Instruction adds six to contents of the accumulator:

CY AC
o 1
1001 1011
0000 0110
1010 0001 = A1H

Now that the most significant bits have a value greater than nine, the instruction adds SIX to them:

CY AC
1 1
1010 0001
0110 0000
0000 0001

When the DAA has finished, the accumulator contains the value 01 in a BCD format; both the carry and auxiliary
carry flags are set ON. Since the actual result of this addition is 101, the carry flag IS probably significant to the
program. The program IS responsible for recovering and using this information. Notice that the carry flag setting is
lost as soon as the program executes any subsequent Instruction that alters the flag.

3-19

Chapter 3. Instruction S ,t

DAD DOUBLE REGISTER ADD

DAD adds ti,e 16-bit value in the specified register pair to the contents of the Hand L register pair. The result
is stored in Hand L.

Opcode Operand

DAD

DAD may add only the contents of the B&C, D&E, H&L, or the SP (Stack Pointer) register pairs to the contents
of H& L. No ice that the letter H must be used to specify that the H& L register pair is to be added to Itself.

DAD sets th ~ carry flag ON if there is a carry out of the Hand L registers. DAD affects none of the condition
flags other han carry.

Cycles: 3
States: 10
Flags: CY

Examples:

The DAD in ;truction provides a means for saving the current contents of the stack pointer.

LXI H,OOH ;CLEAR H&L TO ZEROS
DAD SP ;GET SP INTO H&L
SHLD SAVSP ;STORE SP IN MEMORY

The instruct on DAD H doubles the number in the Hand L registers except when the operation causes a carry
out of the f- register.

DCR DECREMENT

DCR subtra'ts one from the contents of the specified byte. DCR affects all the condition flags except the carry
flag. Becaus( DCR preserves the carry flag, it can be used within multi-byte arithmetic routines for decrementing
character co Jnts and similar purposes.

Decrement I ~egister

Opcode Operand

DCR reg

3-20


The operand must specify one of the registers A through E, H or L. Thp. instruction subtracts one from the
contents of the specified register.

~D D D

Cycles: 1
States: 5 (4 on 8085)
Flags: Z,S,P,AC

Decrement Memory

Opcode Operand

DCR M

This instruction subtracts one from the contents of the memory location addressed by the Hand L registers.
M is a symbol ic reference to the Hand L registers.

10 0 o
Cycles: 3
States: 10
Flags: Z,S,P,AC

Example:

The DCR instruction is frequently used to control multi-byte operations such as moving a number of characters
from one area of memory to another:

MVI B,5H ;SET CONTROL COUNTER
LXI H,260H ;LOAD H&L WITH SOURCE ADDR
LXI D.900H ;LOAD D&E WITH DESTINATION ADDR
LOOP: MOV A,M ;LOAD BYTE TO BE MOVED
STAX D ;STORE BYTE
DCX D ;DECREMENT DESTINATION ADDRESS
DCX M ;DECREMENT SOURCE ADDRESS
DCR B ;DECREMENT CONTROL COUNTER
JNZ LOOP ;REPEAT LOOP UNTIL COUNTER=O

This example also illustrates an efficient programming technique. Notice that the control counter is decremented
to zero rather than incremented until the desired count is reached. This technique avoids the need for a compare
instruction and therefore conserves both memory and execution time.

3-21

Chapter 3. Instruction Sct

DCX DECREMENT REGISTER PAIR

DCX decrerrents the contents of the specified register pair by one. DCX affects none of the condition flags.
Because DC: preserves all the flags, it can be used for address modification in any instruction sequence that
relies on the passing of the flags.

Opcode Operand

DCX

DCX may dlcrement only the B&C, D&E, H&L, or the SP (Stack Pointer) register pairs. Notice that the letter
H must be u;ed to specify the Hand L pair.

Exercise carl' when decrementing the stack pointer as this causes a loss of synchronization between the pointer
and the actual contents of the stack.

Cycles: 1
States: 5 (6 on 8085)
Flags: none

Example:

Assume that the Hand L registers contain the address 9800H when the instruction DCX H is executed. DCX
considers tht: contents of the two registers to be a single 16-bit value and therefore performs a borrow from the
H register te produce the value 97FFH.

DI DISABLE INTERRUPTS

The interruet system is disabled when the processor recognizes an interrupt or Immediately following execution
of a DI instl uction.

In applicaticns that use interrupts, the DI instruction is commonly used only when a code sequence must not be
interrupted. For example, time-dependent code sequences become inaccurate when interrupted. You can disable
the interrup system by including a DI instruction at the beginning of the code sequence. Because you cannot
predict the llccurrence of an interrupt, include an EI instruction at the end of the time-dependent code sequence.

Opcode Operand

DI

Operands an not permitted with the DI instruction.

3-22


1 0 0 11
1

Cycles: 1
States: 4
Flags: none

NOTE

The 8085 TRAP interrupt cannot be disabled. This special interrupt is
intended for serious problems that must be serviced regardless of the
interrupt flag such as power failure or bus error. However. no interrupt
including TRAP can interrupt the execution of the 01 or EI instruction.

EI ENABLE INTERRUPTS

The EI instruction enables the interrupt system following execution of the next program instruction. Enabling
the interrupt system is delayed one instruction to allow interrupt subroutines to return to the main program
before a subsequent interrupt is acknowledged.

In applications that use interrupts, the interrupt system is usually disabled only when the processor accepts an
interrupt or when a code sequence must not be interrupted. You can disable the interrupt system by including
a 01 instruction at the beginning of the code sequence. Because you cannot predict the occurrence of an
interrupt, include an EI instruction at the end of the code sequence.

Opcode Operand

EI

Operands are not permitted With the EI instruction.

o
Cycles: 1
States: 4
Flags: none

NOTE

The 8085 TRAP interrupt cannot be disabled. This special interrupt is
intended for serious problems that must be serviced regardless of the
interrupt flag such as power failure or bus failure. However, no interrupt
including TRAP can interrupt the execution of the 01 or EI instruction.

Example:

The EI instruction is frequently used as part of a start-up sequence. When power is first applied. the processor
begins operating at some indeterminate address_ Application of a RESET signal forces the program counter to

3-23

Chapter 3. Instruction 5 et

zero. A common instruction sequence at this point is El, HLT, These instructions enable the interrupt system
(RESET als" disables the interrupt system) and halt the processor. A subsequent manual or automatic interrupt
then determ Ines the effective start-up address.

HLT HALT

The HLT in ;truction halts the processor. The program counter contains the address of the next sequential
instruction. Jtherwise, the flags and registers remain unchanged.

o
Cycles: 1
States: 7 (5 on 8085)
Flags: none

Once in the halt state, the processor can be restarted only by an external event, typically an interrupt. Therefore,
you should Je certain that interrupts are enabled before the HLT instruction is executed. See the description of
the EI (EnaJle Interrupt) instruction.

If an 8080 I-lLT instruction IS executed while interrupts are disabled, the only way to restart the processor is
by applicatim of a RESET signal. This forces the program counter to zero. The same is true of the 8085, except
for the TR/,P Interrupt, which IS recognized even when the interrupt system is disabled.

The proceSSJr can temporarily leave the halt state to service a direct memory access request. However, the pro-
cessor reent~rs the halt state once the request has been serviced.

A basic purpose for the HLT instruction is to allow the processor to pause while waiting for an interrupt from a
peripheral d~vice. However, a halt wastes processor resources and should be used only when there is no useful
processing t Isk available.

IN INPUT FROM PORT

The IN inst uction reads eight bits of data from the specified port and loads it into the accumulator.

NOTE

fhis description IS restricted to the exact function of the IN instruction.
Input/output structures are described in the 8080 or 8085 Microcomputer
Systems User's Manual.

Opcode Operand

IN exp

The operand expression may be a number or any expression that yields a value in the range OOH through OFFH.

3·24


° °
exp

Cycles: 3
States: 10
Addressing: direct
Flags: none

INR INCREMENT

INR adds one to the contents of the specified byte. INR affects all of the condition flags except the carry flag.
Because INR preserves the carry flag, it can be used within multi-byte arithmetic routines for incrementing
character counts and similar purposes.

Increment Register

Opcode Operand

INR reg

The operand must specify one of the registers A through E, H or L. The Instruction adds one to the contents of
the specified register,

~I D D D 1_
_ 0_01

Cycles: 1
States: 5 (4 on 8085)
Flags: Z,S,P,AC

Increment Memory

Opcode Operand

INR M

This instruction increments by one the contents of the memory location addressed by the Hand L registers. M
is a symbolic reference to the Hand L registers.

1° ° ° ° °I
Cycles: 3
States: 10
Flags: Z,S,P,AC

3·25

Chapter 3. Instruction 5 ,t

Example:

If register C contains 99H, the instruction INR C increments the contents of the register to 9AH.

INX INCREMENT REGISTER PAIR

INX adds olle to the contents of the specified register pair. INX affects none of the condition flags. Because
INX preserVlS all the condition flags, it can be used for address modification within multi-byte arithmetic
routines.

Opcode Operand

INX

INX may lIl;rement only the B&C, D&E, H& L, or the SP (Stack Pointer) register pairs. Notice that the letter H
must be usd to specify the Hand L register pair.

Exercise caro when incrementing the stack pOlllter. Assume, for example, that INX SP IS executed after a number
of Items ha' e been pushed onto the stack. A subsequent POP instruction accesses the high-order byte of the most
recent stack entry and the low-order byte of the next older entry. Similarly, a PUSH Instruction adds the two
new bytes t) the stack, but overlays the low-order byte of the most recent entry

Cycles: 1
States: 5 (6 on 8085)
Addresslllg: register
Flags: none

Example:

Assume tha. the D and E registers contalll the value 01 FFH. The instruction INX D increments the value to
0200H. By ;ontrast, the INR E Instruction ignores the carry out of the low-order byte and produces a result of
0100H. (Tills condition can be detected by testing the Zero condition flag.)

If the stack pointer register contallls the value OFFFFH, the instruction INX SP increments the contents of SP
to OOOOH. --he INX instruction sets no flags to IIldicate this condition.

JC JUMP IF CARRY

The JC instruction tests the setting of the carry flag. If the flag is set to one, program execution resumes at the
address spe;ified in the JC instruction. If the flag is reset to zero, execution continues with the next sequential
instruction.

3-26


Opcode Operand

JC address

The address may be specified as a number, a label, or an expression. The assembler inverts the high and low
address bytes when it assembles the instruction.

1 1 0 1 1 0 1 0

lowaddr

high addr

Cycles: 3 (2 or 3 on 8085)
States: 10 (7 or 10 on 8085)
Flags: none

Example:

Examples of the variations of the jump instruction appear in the description of the JPO instruction.

JM JUMP IF MINUS

The JM Instruction tests the setting of the sign flag. If the contents of the accumulator are negative (sign flag = 1),
program execution resumes at the address specified In the Jrv1 instruction. If the contents of the accumulator are
positive (sign flag = 0), execution continues with the next sequential instruction.

Opcode Operand

JM address

address bytes when it assembles the instructions.

1 1 1 1 1 0 1 0

lowaddr

high addr

CYcles: 3 (2 or 3 on 8085)
States: 10 (7 or 10 on 8085)
Flags: none

Example:

Examples of the variations of the lump instruction appear in the description of the JPO instruction.

3-27


JMP JUMP

The IMP inst"uction alters the execution sequence by loading the address in its second and third bytes into the
program courter.

Opeode Operand

IMP address

The address rnay be specified as a number, a label, or an expression. The assembler inverts the high and low
address bytes when it assembles the address.

1 1 0 0 0 0 1 1

lowaddr

high addr

Cycles: 3
States: 10
Flags: none

Example:

Examples of the variations of the Jump instruction appear in the description of the JPO instruction.

JNC JUMP IF NO CARRY

The INC ins;ruction tests the setting of the carry flag. If there is no carry (carry flag = 0), program execution
resumes at ti,e address specified in the I NC instruction. If there is a carry (carry flag = 1), execution continues
with the nex t sequential Instruction.

Ooeode Operand

INC address

The address nay be specified as a number, a label, or an expression. The assembler inverts the high and Jow
address byte; when it assembles the instruction.

1 1 0 1 0 0 1 0

lowaddr

high addr

Cycles: 3 (2 or 3 on 8085)
States: 10 (7 or 10 on 8085)
Flags: none
3-28


Example:

Examples of the variations of the jump instruction appear in the description of the JPO Instruction.

JNZ JUMP IF NOT ZERO

The J NZ Instruction tests the setting of the zero flag. If the contents of the accumulator are not zero (zero
flag = 0), program execution resumes at the address specified In the JNZ instruction. If the contents of the
accumulator are zero (zero flag = 1), execution continues with the next sequential instruction.

Opcode Operand

JNZ address


1 1 0 0 0 0 1 0

lowaddr

high addr

Cycles: 3 (2 or 3 on 8085)
States: 10 (7 or 10 on 8085)
AddreSSing: immediate
Flags: none

Example:

Examples of the variations of the lump instruction appear In the description of the J PO instruction.

JP JUMP IF POSITIVE

The JP instruction tests the setting of the sign flag. If the contents of the accumulator are positive (sign flag = 0),
program execution resumes at the address specified in the JP Instruction. If the contents of the accumulator are
=
minus (sign flag 1), execution continues with the next sequential instruction.

Opcode Operand

JP address

The address may be specified as a number, a label, or an expression. The assembler inverts the high and low order

3-29

Chapter 3. Instruction 51 t

1 1 1 1 0 0 1 0

lowaddr

high addr

Cycles: 3 (2 or 3 on 8085)
States: 10 (7 or 10 on 8085)
Addressi ng: immediate
Flags: none

Example:

Examples of the variations of the lump instruction appear in the description of the JPO instruction.

JPE JUMP IF PARITY EVEN

Parity IS evell if the byte In the accumulator has an even number of one bits. The parity flag IS set to one to
indicate this condition.

The J PE Instruction tests the setting of the parity flag. If the parity flag is set to one, program execution resumes
at the addre~ s specified in the J PE instruction. If the flag IS reset to zero, execution continues with the next
sequential in ;truction.

Opcode Operand

JPE address

address byte, when it assembles the instruction.

The J PE anc J PO (jump if parity odd) instructions are especially useful for testing the parity of input data.
However, th., IN instruction does not set any of the condition flags. The flags can be set by adding OOH to the
contents of .he accumulator.

1 1 1 0 1 0 1 0

lowaddr

high addr

Cycles: 3 (2 or 3 on 8085)
States: 10 (7 or 10 on 8085)
Addressing: Immediate
Flags: none

Example:

Examples 01 the variations of the lump instruction appear In the deSCrIption of the J PO instruction.

3-30


JPO JUMP IF PARITY ODD

Parity is odd if the byte in the accumulator has an odd number of one bits. The parity flag is set to zero to
indicate this condition.

The JPO Instruction tests the setting of the parity flag. If the parity flag is reset to zero, program execution
resumes at the address specified in the JPO instruction. If the flag is set to one. execution continues with the
next sequential instruction.

Opcode Operand

JPO address

The address may be specified as a number. a label. or an expression. The assembler Inverts the high and low

The JPO and JPE (jump if panty even) instructions are especially useful for testing the parity of Input data.
However. the IN instruction does not set any of the condition flags. The flags can be set by adding OOH to the
contents of the accumulator.

1 1 1 0 0 0 1 0

low addr

high addr

Cycles: 3 (2 or 3 on 8085)
States: 10 (7 or 10 on 8085)
Flags: none

Example:

This example shows three different but equivalent methods for lumping to one of two points in a program based
upon whether or not the Sign bit of a number is set. Assume that the byte to be tested IS the C register.

Label Code Operand

ONE: MOV A.C
ANI 80H
JZ PLUS
JNZ MINUS
TWO: MOV A.C
RLC
JNC PLUS
JMP MINUS
THREE: MOV A.C
ADI 0
JM MINUS
PLUS: ;SIGN BIT RESET
MINUS: ;SIGN BIT SET
3-31


The AND iinmediate instruction in block ONE zeroes all bits of the data byte except the Sign bit, which re-
mains unch lnged. If the Sign bit was zero, the Zero condition bit will be set, and the JZ instruction will cause
program coltrol to be transferred to the Instruction at PLUS. Otherwise, the JZ instruction will merely update
the progranl counter by three, and the JNZ instruction will be executed, causing control to be transferred to
the instruct ion at MINUS. (The Zero bit IS unaffected by all jump instructions.)

The RLC illstruction in block TWO causes the Carry bit to be set equal to the Sign bit of the data byte. If the
Sign bit wai reset, the JNC instruction causes a lump to PLUS. Otherwise the JMP instruction is executed,
unconditiollally transferring control to MINUS. (Note that, in this instance, a JC instruction could be sub-
stituted for the unconditional jump with identical results.)

The add irrmediate instruction In block THREE causes the condition bits to be set. If the sign bit was set, the
J M instruction causes program control to be transferred to MINUS. Otherwise, program control flows auto-
matically ino the PLUS routine.

JZ JUMP IF ZERO

The J Z Ins",ruction tests the setting of the zero flag. If the flag is set to one, program execution resumes at the
address spe~ified in the JZ instruction. If the flag is reset to zero, execution continues with the next sequential
Instruction

Opcode Operand

JZ address

The addresi may be specified as a number, a label, or an expression. The assembler inverts the high and low
address by! es when it assembles the instruction.

1 1 0 0 1 0 1 0

low addr

high addr

Cycles: 3 (2 or 3 on 8085)
States: 10 (7 or lOon 8085)
Flags: none

Example:

Examples )f the variations of the jump instruction appear In the deswptlon of the JPO instruction.

LOA LOAD ACCUMULATOR DIRECT

LDA load~ the accumulator with a copy of the byte at the location specified In bytes two and three of the
LDA instr Jction.

3-32


Opcode Operand

LDA address

The address may be stated as a number. a previously defined label. or an expression. The assembler inverts the
high and low address bytes when it builds the instruction.

0 0 1 1 1 0 1 0

lowaddr

high addr

CYcles: 4
States: 13
Addressing: direct
Flags: none

Examples:

The following instructions are equivalent. When executed. each replaces the accumulator contents with the byte
of data stored at memory location 300H.

LOAD: LDA 300H
LDA 3*{16*16)
LDA 200H+256

LDAX LOAD ACCUMULATOR INDIRECT

L DAX loads the accumulator with a copy of the byte stored at the memory location addressed by register pair
B or register pair D.

Opcode Operand

LDAX

The operand B specifies the Band C register pair: D specifies the D and E register pair. This instruction may
specify only the B or D register pair.

10 0 0
-'--------I
I~ 0 0

I fo '" register pair B
II '" register pair D

Cycles: 2
States: 7
Flags: none

3-33

Chapter 3. Instruction :,et

Example:

Assume that register D contains 93H and register E contains 8BH. The following instruction ioads the accumulator
with the contents of memory location 938BH:

LDAX D

LHLD LOAD HAND L DIRECT

LHLD loads the L register with a copy of the byte stored ilt the memory location specified in bytes two and
three of the LHLD instruction. LHLD then loads the H register with a copy of the byte stored at the next
higher memory location.

Opcode Operand

LHLD address

The address may be stated as a number, a label, or an expression.

Certain instl uctions use the symbolic reference M to access the memory location currently specified by the Hand
L registers. _HLD is one of the instructions provided for loading new addresses into the Hand L registers. The
user may al:o load the current top of the stack into the Hand L registers (POP instruction). Both LHLD and
POP replace the contents of the Hand L registers. You can also exchange the contents of Hand L with the D
and E regist~rs (XCHG instruction) or the top of the stack (XTHL instruction) if you need to save the current
Hand L registers for subsequent use. SHLD stores Hand L in memory.

0 0 1 0 1 0 1 0

lowaddr

high addr

Cycles: 5
States: 16
Addressing: direct
Flags: none

Example:

Assume that locations 3000 and 3001 H contain the address 064EH stored in the format 4E06. In the following
sequence, tlie MaY instruction moves a copy of the byte stored at address 064E into the accumulator:

LHLD 3000H ;SET UP ADDRESS
MaY A,M ;LOAD ACCUM FROM ADDRESS

3·34


LXI LOAD REGISTER PAIR IMMEDIATE

LXI is a three-byte instruction; its second and third bytes contain the source data to be loaded into a register
pair. LXI loads a register pair by copying its second and third bytes into the specified destination register pair.

Opcode Operand

LXI

The first operand must specify the register pair to be loaded. LXI can load the Band C register pair, the D and
E register pair, the Hand L register pair, or the Stack Pointer.

The second operand specifies the two bytes of data to be loaded. This data may be coded in the form of a num-
ber, an ASCII constant, the label of some previously defined value, or an expression. The data must not exceed
two bytes.

LXI is the only immediate instruction that accepts a 16-bit value. All other immediate instructions require 8-bit
values.

Notice that the assembler inverts the two bytes of data to create the format of an address stored in memory.
LXI loads its third byte into the first register of the pair and its second byte into the second register of the
pair. This has the effect of reinverting the data into the format required for an address stored in registers. Thus,
the instruction LXI S,'AZ' loads A Into register Band Z into register C.

0 o I R P I0 0 0 1

low-order data

high-order data

Cycles: 3
States: 10
Flags: none

Examples:

A common use for LXI is to establish a memory address for use in subsequent instructions. In the following
sequence, the LXI instruction loads the address of STRNG into the Hand L registers. The MOV instruction then
loads the data stored at that address into the accumulator.

LXI H,STRNG ;SET ADDRESS
MOV A,M ;LOAD STRNG INTO ACCUMULATOR

The following LXI instruction is used to initialize the stack pointer in a relocatable module. The LOCATE pro-
gram provides an address for the special reserved label STACK.

LXI SP,STACK
3-35

Chapter 3. Instruction 5et

MOV MOVE

The MOV in~ tructlon moves one byte of data by copying the source field into the destination field. Source data
remains unchanged. The instruction's operands specify whether the move is from register to register, from a
register to m"mory, or from memory to a register.

Move Reglsur to Register

Opcode Operand

MOV regl,reg2

The instructi)n copies the contents of reg2 into regl. Each operand must specify one of the registers A, B, C, D,
E, H, or L.

When the sal ne register is specified for both operands (as in MOV A,A), the MOV functions as a NOP (no opera-
tion) since it has no other noticeable effect. This form of MOV requires one more machine state than NOP, and
therefore ha~ a slightly longer execution time than NOP. Since M addresses a register pair rather than a byte of
data, MOV H,M is not allowed.

G D D Dis 5 51
Cycles: 1
States: 5 (4 on 8085)
Flags: none

Move to Men'lOry

Opcode Operand

MOV M,r

This instruct ion copies the contents of the specified register Into the memory location addressed by the Hand L
registers. M s a symbolic reference to the Hand L register pair. The second operand must address one of the
registers.

1,--0 0 Is 5 51
Cycles: 2
States: 7
Flags: none

Move from .Vlemory

Opcode Operand

MOV r,M

3-36


This instruction copies the contents of the memory location addressed by the Hand L registers into the specified
register. The first operand must name the destination register. The second operand must be M. M is a symbolic
reference to the Hand L registers.

CID 0 °I 01
Cycles: 2
States: 7
Flags: none

Examples:

Label Opcode Operands Comment

LDACC: MOV A,M ;LOAD ACCUM FROM MEMORY
MOV E,A ;COPY ACCUM INTO E REG
NULOP: MOV C,C ;NULL OPERATION

MVI MOVE IMMEDIATE

MVI is a two-byte instruction; its second byte contains the source data to be moved. MVI moves one byte of
data by copying its second byte into the destination field. The instruction's operands specify whether the move
is to a register or to memory.

Move Immediate to Register

Opcode Operand

MVI reg,data

The first operand must name one of the registers A through E, H or L as a destination for the move.

The second operand specifies the actual data to be moved. This data may be in the form of a number, an ASCII
constant, the label of some previously defined value, or an expression. The data must not exceed one byte.


data

Cycles: 2
States: 7
Flags: none

3-37

Chapter 3. Instruction iet

Move Immediate to Memory

Opcode Operand

MVI M,data

This instruc:ion copies the data stored in its second byte into the memory location addressed by Hand L. M is
a symbolic eference to the Hand L register pair.

o 0 o o
data

Cycles: 3
States: 10
AddreSSing: Immediate/register indirect
Flags: none

Examples:

The followilg examples show a number of methods for defining immediate data In the MVI instruction. All of
the exampk s generate the bit pattern for the ASCII character A.

MVI M,01000001B
MVI M:A'
MVI M.41H
MVI M,101Q
MVI M,65
MVI M,5+30*2

NOP NO OPERATION

NOP perfor TIS no operation and affects none of the condition flags. NOP IS useful as filler in a timing loop.

Opcode Operand

NOP

Operands al e not permitted with the NOP instruction.

ORA INCLUSIVE OR WITH ACCUMULATOR

ORA perf01 ms an inclusive OR logical operation uSing the contents of the specified byte and the accumulator. The
result is pla:ed in the accumulator.

3-38


Summary of Logical Operations

AND produces a one bit in the result only when the corresponding bits in the test data and the mask data are
one.

OR produces a one bit in the result when the corresponding bits in either the test data or the mask data are
ones.

different; i.e., a one bit in either the test data or the mask data - but not both - produces a one bit in the
result.

AND OR EXCLUSIVE OR

1010 1010 1010 1010 1010 1010
0000 1111 0000 1111 0000 1111
00001010 1010 1111 1010 0101

OR Register with Accumulator

Opcode Operand

ORA reg

The operand must specify one of the registers A through E, H or L. This instruction ORs the contents of the
specified register and the accumulator and stores the result in the accumulator. The carry and auxiliary carry
flags are reset to zero.

o oIss S I
Cycles: 1
States: 4
Flags: Z,S,P,CY,AC

OR Memory with Accumulator

Opcode Operand

ORA M

The contents of the memory location specified by the Hand L registers are inciusive-oRed with the contents of
the accumulator. The result is stored in the accumulator. The carry and auxiliary carry flags are reset to zero.

o o
Cycles: 2
States: 7
Flags: Z,S,P,CY,AC

3-39


Example:

Since any tit inciusive-ORed with a one produces a one and any bit ORed with a zero remains unchanged, ORA
is frequentl y used to set ON particular bits or groups of bits. The following example ensures that bit 3 of the
accumulator is set ON, but the remaining bits are not disturbed. This is frequently done when individual bits
are used as status flags in a program. Assume that register D contains the value OSH:

Register D o 0 0 0 1 000
01001011

ORI INCLUSIVE OR IMMEDIATE

ORI performs an inclusive OR logical operation using the contents of the second byte of the instruction and the
contents 01 the accumulator, The result is placed in the accumulator. ORI also resets the carry and auxiliary
carry flags to zero.

Opcode Operand

ORI data

The operar d must specify the data to be used In the inclusive OR operation. This data may be in the form of a
number, ar ASCII constant, the label of some previously defined value, or an expression. The data may not
exceed one byte.

When neitrer operator is present, the assembler assume the LOW operator and issues an error message.

o o

data

Cycles: 2
States: 7
Flags: Z,S,P,SY,AC

Summary, If Logical Operations

AND prod Jces a one bit in the result only when the corresponding bits in both the test data and the mask data
are ones.

OR prodU< es a one bit in the result when the corresponding bits in either the test data or the mask data are ones.

different; I.e., a one bit in either the test data or the mask data - but not both produces a one bit in the
result.

3-40


AND OR EXCLUSIVE OR

1010 1010 1010 1010 1010 1010
00001111 00001111 0000 1111
00001010 1010 1111 10100101

Example:

See the description of the ORA instruction for an example of the use of the inclusive OR. The following
examples show a number of methods for defining immediate data in the ORI instruction. All of the examples
generate the bit pattern for the ASCII character A.

ORI 01000001B
ORI 'A'
ORI 41H
ORI 101Q
ORI 65
ORI 5+30*2

OUT OUTPUT TO PORT

The OUT instruction places the contents of the accumulator on the eight-bit data bus and the number of the
selected port on the sixteen-bit address bus. Since the number of ports ranges from 0 through 255, the port
number is duplicated on the address bus.

It is the responsibility of external logic to decode the port number and to accept the output data.

NOTE

Because a discussion of input/output structures is beyond the scope of
this manual, this description is restricted to the exact function of the
OUT instruction. Input/output structures are described in the 8080 or
8085 Microcomputer Systems User's Manual.

Opcode Operand

OUT exp

The operand must specify the number of the desired output port. This may be in the form of a number or an
expression in the range OOH through OFFH.

1 0 0 0
1 I
I exp

Cycles: 3
States: 10
Addressing: direct
Flags: none
3·41


PCHL MOVE H&L TO PROGRAM COUNTER

PCHL loads tle contents of the Hand L registers Into the program counter register. Because the processor
fetches the next instruction from the updated program counter address, PCHL has the effect of a iump instruc-
tion.

Opcode Operand

PCHL

Operands are not permitted with the PCHL instruction.

PCHL moves the contents of the H register to the high-order eight bits of the program counter and the contents
of the L regHer to the low-order eight bits of the program counter.

The user pro'~ram must ensure that the Hand L registers contain the address of an executable instruction when
the PCHL In: truction is executed.

o o 0 1 I
Cycles: 1
States: 5 (6 on 8085)
AddreSSing: register
Flags: none

Example:

One techniqlle for passing data to a subroutine IS to place the data Immediately after the subroutine call. The
return addre, s pushed onto the stack by the CALL Instruction actually addresses the data rather than the next
instruction ater the CALL. For tillS example, assume that two bytes of data follow the subroutine call. The
following coding sequence performs a return to the next Instruction after the call:

GO BACK: POP H ;GET DATA ADDRESS
INR L ;ADD 2 TO FORM
INR L ;RETURN ADDRESS
PCHL ;RETURN

POP POP

The POP ins:ruction removes two bytes of data from the stack and copies them to a register pair or copies the
Program Stttus Word into the accumulator and the condition flags.

POP Registe, Pair

POP copies: he contents of the memory location addressed by the stack pointer Into the low-order register of the
register pair POP then increments the stack pointer by one and copies the contents of the resulting address into

3-42


the high-order register of the pair. POP then increments the stack pointer again so that it addresses the next
older Item on the stack.

Opcode Operand

POP

The operand may specify the B&C, D&E, or the H&L register pairs. POP PSW is explained separately.

~ R pi 0 0 0 11
Cycles: 3
States: 10
Flags: none

POP PSW

POP PSW uses the contents of the memory location specified by the stack pointer to restore the condition flags.
POP PSW increments the stack pointer by one and restores the contents of that address to the accumulator.
POP then increments the stack pointer again so that it addresses the next older item on the stack.

Cycles: 3
States: 10
Flags: Z,S,P,CY,AC

Example:

Assume that a subroutine is called because of an external interrupt. In general, such subroutines should save and
restore any registers it uses so that main program can continue normally when it regains control. The following
sequence of PUSH and POP instructions save and restore the Program Status Word and all the registers:

343

Chapter 3. Instruction :,et

PUSH PSW
PUSH B
PUSH D
PUSH H

subroutine coding

POP H
POP D
POP B
POP PSW
RET

Notice that the sequence of the POP instructions is the opposite of the PUSH instruction sequence.

PUSH PUSH

The PUSH ilstruction copies two bytes of data to the stack. This data may be the contents of a register pair or
the Progran Status Word. as explained below:

PUSH Regis'er Pair

PUSH decrements the stack pointer register by one and copies the contents of the high-order register of the
register pair to the resulting address. PUSH then decrements the pointer again and copies the low-order register
to the resuh ing address. The source registers remain unchanged.

Opcode Operand

PUSH
{U
The operand may specify the B&C. D&E. or H&L register pairs. PUSH PSW is explained separately.

Cycles: 3
States: 11 (13 on 8085)
Addressi ng: register indirect
Flags: none

Example:

Assume tha: register B contains 2AH. the C register contains 4CH, and the stack pOinter is set at 9AAF. The
instruction'USH B stores the B register at memory address 9AAEH and the C register at 9AADH. The stack
pointer is st:t to 9AADH:

344


Stack Stack
Before PUSH Address After PUSH

SP before .. xx 9AAF xx
xx
xx
xx
9AAE
9AAD
9AAC
2A
4C
xx
.. SP after

PUSH PSW

PUSH PSW copies the Program Status Word onto the stack. The Program Status Word comprises the contents
of the accumulator and the current settings of the condition flags. Because there are only five condition flags,
PUSH PSW formats the flags Into an eight-bit byte as follows:

7 6 5 4 3 2 o
~AC 0 P I CY I
On the 8080, bits 3 and 5 are always zero; bit one is always set to one. These filler bits are undefined on the
8085.

PUSH PSW decrements the stack pointer by one and copies the contents of the accumulator to the resulting
address. PUSH PSW again decrements the pointer and copies the formatted condition flag byte to the resulting
address. The contents of the accumulator and the condition flags remain unchanged.

o
Cycles: 3
States: 11 (120n8085)
Flags: none

Example:

When a program calls subroutines, it is frequently necessary to preserve the current program status so the calling
program can continue normally when it regains control. Typically, the subroutine performs a PUSH PSW prior to
execution of any instruction that might alter the contents of the accumulator or the condition flag settings.
The subroutine then restores the pre-call system status by executing a POP PSW instruction just before returning
control to the calling program.

RAL ROTATE LEFT THROUGH CARRY

RAL rotates the contents of the accumulator and the carry flag one bit position to the left. The carry flag, which
is treated as though it were part of the accumulator, transfers to the low-order bit of the accumulator. The high-
order bit of the accumulator transfers into the carry flag.

Opcode Operand

RAL

Operands are not permitted with the RAL instruction.
345

Chapter 3. Instruction S"t

10 0 0 o
Cycles: 1
States: 4
Flags: CYonly

Example:

Assume that the accumulator contains the value OAAH and the carry flag is zero. The following diagrams illus-
trate the eff, ct of the RAL instruction:

Before Carry

o }--------..,
Accumulator

o o o o

After: Carry

DJ
Accumulator

1
0 0 0 0 01

RAR ROTATE RIGHT THROUGH CARRY

RAR rotate~ the contents of the accumulator and the carry flag one bit position to the right. The carry flag,
which is tre2ted as though it were part of the accumulator. transfers to the high-order bit of the accumulator.
The low-ord"r bit of the accumulator transfers into the carry flag.

Opcode Operand

RAR

Operands an' not permitted with the RAR instruction.

10 0 0

Cycles: 1
States: 4
Flags: CYonly

3-46


Example:

Assume that the accumulator contains the value OAAH and the carry flag is zero. The following diagrams illus-
trate the effect of the RAR instruction:

Before: Carry

0

Accumulator

0 0 0 0

After: Carry

~
Accumulator

1
0 0 0 0 1 I
RC RETURN IF CARRY

The RC instruction tests the carry flag. If the flag is set to one to indicate a carry. the instruction pops two
bytes off the stack and places them in the program counter. Program execution resumes at the new address in
the program counter. If the flag is zero, program execution simply continues with the next sequential instruction.

Opcode Operand

RC

Operands are not permitted with the RC instruction.

o o 0 0 I
Cycles: 1 or 3
States: 5 or 11 (6 or 12 on 8085)
Flags: none

Example:

For the sake of brevity. an example is given for the RET instruction but not for each of its closely related
variants.

347


RET RETURN FROM SUBROUTINE

The RET irstruction pops two bytes of data off the stack and places them In the program counter register.
Program ex,:cution resumes at the new address In the program counter.

Typically, I:ET instructions are used in conjunction with CALL instructions. (The same IS true of the variants
of these instructions.) In this case, it IS assumed that the data the RET instruction pops off the stack is a
return addr:ss placed there by a previous CALL. This has the effect of returning control to the next Instruction
after the CILL. The user must be certain that the RET instruction finds the address of executable code on the
stack. If th,' instruction finds the address of data, the processor attempts to execute the data as though it were
code.

Opcode Operand

RET

Operands a'e not permitted with the RET Instruction.

o 0 o 0

Cycles: 3
States: 10
Flags: none

Example:

As mentior ed previously, subroutines can be nested. That is, a subroutine can call a subroutine that calls
another sul,routine. The only practical limit on the number of nested calls is the amount of memory available
for stackin:; return addresses. A nested subroutine can even call the subroutine that called it, as shown In the
follOWing example. (Notice that the program must contain logic that eventually returns control to the main
program. Ctherwlse, the two subroutines will call each other indefinitely.)

1~
MAlt1 PROGRAM

SUBA r--~---CALLSUBA
1 SUBB

CILL SUBA CNZ S U B ~ T
T T - RET

RET ....

RIM (8085 PRO::ESSOR ONLY) READ INTERRUPT MASK

The RIM ilstruction loads eight bits of data into the accumulator. The resulting bit pattern indicates the current
setting of . he interrupt mask, the setting of the interrupt flag, pending interrupts, and one bit of serial input data,
if any.

348


Opcode Operand

RIM

Operands are not permitted with the RIM instruction.

The RIM instruction loads the accumulator with the following information:

I 7 6 5 4 3 2 1 0

I SID 17 16 15 IE 7.5 6.5 5.5

"--v-' "---v---" V '---v----"
I L

L
Interrupt Masks: 1 = masked

Llnterrupt Enable Flag: = enabled

Pending Interrupts: 1 = pending
'----Serial Input Data Bit. if any

The mask and pending flags refer only to the RST5.5, RST6.5, and RST7.5 hardware interrupts. The IE flag
refers to the entire interrupt system. Thus, the IE flag is identical in function and level to the INTE pin on the
8080. A 1 bit in this flag indicates that the entire interrupt system is enabled.

0 0 0 0 0 0 01
1
Cycles: 1
States: 4
Flags: none

RLC ROTATE ACCUMULATOR LEFT

RLC sets the carry flag equal to the high-order bit of the accumulator, thus overwriting its previous setting. RLC
then rotates the contents of the accumulator one bit position to the left with the high-order bit transferring to
the low-order position of the accumulator.

Opcode Operand

RLC

Operands are not allowed with the RLC instruction.

10 0 0 0 0

Cycles: 1
States: 4
Flags: CYonly

349

Chapter 3. Instruction S,t

Example:

Assume that tne accumulator contains the value OAAH and the carry flag is zero. The following diagrams illus-
trate the effect of the RLC instruction.

Before: Carry

0

Accumulator

0 0 0 0

After: Carry

Q
Accumulator

1
0 0 0 0 1[

RM RETURN IF MINUS

The RM instr Jction tests the sign flag. If the flag is set to one to indicate negative data in the accumulator, the
instruction pcps two bytes off the stack and places them in the program counter, Program execution resumes at
the new addr,'ss In the program counter. If the flag is set to zero, program execution simply continues with the
next sequentlll instruction.

Opcode Operand

RM

Operands are not permitted with the RM instruction.

o 0 01
Cycles: 1 or 3
States: 5 or 11 (6 or 12 on 8085)
Flags: none

Example:

For the sake of brevity, an example is given for the RET instruction but not for each of its closely related
variants.

3-50


RNC RETURN IF NO CARRY

The RNC instruction tests the carry flag. If the flag is set to zero to indicate that there has been no carry, the
instruction pops two bytes off the stack and places them in the program counter. Program execution resumes at
the new address in the program counter. If the flag is one, program execution simply continues with the next
sequential instruction.

Opcode Operand

RNC

Operands are not permitted with the RNC instruction.

a a a a 01
Cycles: 1 or 3
States: 5 or 11 (6 or 12 on 8085)
Flags: none

Example:

For the sake of breVity. an example is given for the RET instruction but not for each of its closely related
variants.

RNZ RETURN IF NOT ZERO

The RNZ instruction tests the zero flag. If the flag is set to zero to indicate that the contents of the accumulator
are other than zero. the instruction pops two bytes off the stack and places them in the program counter. Pro-
gram execution resumes at the new address in the program counter. If the flag is set to one. program execution
simply continues with the next sequential instruction.

Opcode Operand

RNZ

Operands are not permitted with the RNZ instruction.

11 a a a a a 01
Cycles: 1 or 3
States: 501'11 (601' 12 on 8085)
Flags: none

Example:

For the sake of brevity. an example IS given for the RET instruction but not for each of its closely related
variants.

3-51

Chapter 3. Instruction S"t

RP RETURN IF POSITIVE

The RP instnlction tests the sign flag. If the flag is reset to zero to indicate positive data in the accumulator,
the instruction pops two bytes off the stack and places them in the program counter. Program execution
resumes at the new address in the program counter. If the flag is set to one, program execution simply continues

Opcode Operand

RP

Operands are not permitted with the RP instruction.

o 0 0 01

Cycles: 1 or 3
States: 5 or 11 (6 or 12 on 8085)
Flags: none

Example:

variants.

RPE RETURN IF PARITY EVEN

Parity is ever if the byte in the accumulator has an even number of one bits. The parity flag IS set to one to
indicate this ;ondition. The RPE and RPO instructions are useful for testing the parity of input data. However,
the IN instru;tion does not set any of the condition flags. The flags can be set without altering the data by

The RPE ins', ruction tests the parity flag. If the flag is set to one to indicate even parity, the instruction pops
two bytes of' the stack and places them in the program counter. Program execution resumes at the new address
in the program counter. If the flag IS zero. program execution simply continues with the next sequential instruc-
tion.

Opcode Operand

RPE

Operands are not permitted with the RPE instruction.

o o 0 01
Cycles: 1 or 3
States: 5 or 11 (6 or 12 on 8085)
Flags: none

3-52


Example:

For the sake of brevity, an example IS given for the RET instruction but not for each of its closely related
variants.

RPO RETURN IF PARITY ODD

Parity is odd if the byte in the accumulator has an odd number of one bits. The parity flag is reset to zero to
indicate this condition. The RPO and RPE instructions are useful for testing the parity of input data. However,
the IN instruction does not set any of the condition flags. The flags can be set without altering the data by

The RPO instruction tests the parity flag. If the flag is reset to zero to indicate odd parity, the instruction pops
two bytes off the stack and places them in the program counter. Program execution resumes at the new address
in the program counter. If the flag is set to one, program execution simply continues with the next sequential
instruction.

Opcode Operand

RPO

Operands are not permitted with the RPO instruction.

o 0 0 0 01

Cycles: 1 or 3
States: 5 or 11 (6 or 12 on 8085)
Flags: none

Example:

variants.

RRC ROTATE ACCUMULATOR RIGHT

RRC sets the carry flag equal to the low-order bit of the accumulator, thus overwriting its previous setting. RRC
then rotates the contents of the accumulator one bit position to the right with the low-order bit transferring to
the high order position of the accumulator.

Opcode Operand

RRC

Operands are not permitted with the RRC instruction.

3-53


10 0 0 0

Cycles:
States: 4
Flags: CYonly

Example:

Assume that the accumulator contains the value OAAH and the carry flag is zero. The folloving diagrams illus-
trate the effect of the RRC instruction:

Before: Carry

G
Accumulator

0 0 0

After: Carry

G
Accumulator

0 0 0 0 1
1

RST RESTART

RST IS a special purpose CALL instruction designed primarily for use with interrupts. RST !,ushes the contents
of the program counter onto the stack to provide a return address and then Jumps to one 0 eight predetermined
addresses. A three-bit code carried in the opcode of the RST instruction specifies the Jump ,Iddress.

The restart instruction IS unique because it seldom appears as source code 111 an applications program. More often,
the peripheral devices seekll1g interrupt service pass this one-byte instruction to the processcr,

When a deVice requests interrupt service and lI1terrupts are enabled, the processor acknowlecges the request and
prepares its data lines to accept anyone-byte instruction from the deVice. RST is generally he instruction of
chOice because its special purpose CALL establishes a return to the main program.

The processor moves the three-bit address code from the RST instruction into bits 3, 4, ane 5 of the program
counter. In effect, this multiplies the code by eight. Program execution resumes at the new address where eight
bytes are available for code to service the interrupt. If eight bytes are too few, the program can either Jump to
or call a subroutine.

3-54


8085 NOTE

The 8085 processor Includes four hardware inputs that generate internal RST
instructions. Rather than send a RST instruction, the interrupting device need
only apply a signal to the RST5.5, RST6.5, RST7.5, or TRAP input pin.
The processor then generates an internal RST instruction. The execution
depends on the input:

INPUT RESTART
NAME ADDRESS

TRAP 24H
RST5.5 2CH
RST6.5 34H
RSn.5 3CH

Notice that these addresses are within the same portion of memory used by the RST instruction, and therefore
allow only four bytes - enough for a call or jump and a return for the interrupt service routine.

If Included in the program code, the RST instruction has the following format:

Opcode Operand

RST code

The address code must be a number or expreSSion within the range 0008 through 1118.

11 IC
~
C r
'" I1 11

Progrdm --~

Counter 15 14 13 12 11 10 9 8 7 6 5 4 3 2 0

After RST 10 0 0 0 0 0 0 0 0 0 C C C 0 0 01

Cycles: 3
States: 11 (12 on 8085)
Flags: none

RZ RETURN IF ZERO

The RZ instruction tests the zero flag. If the flag IS set to one to indicate that the contents of the accumulator are
zero, the instruction pops two bytes of data off the stack and places them in the program counter. Program
execution resumes at the new address in the program counter. If the flag is zero, program execution simply
continues with the next sequential instruction.

3-55


Gpcode Operand

RZ

Operands are not permitted with the RZ instruction.

o 0 o 0 01
Cycles: 1 or 3
States: 5 or 11 (6 or 12 on 8085)
Flags: none

Example:

For the sake of brevity. an example is given for the RET instruction but oot for each of its closely related
variants.

SBB SUBTRACT WITH BORROW

SBB subtracts one byte of data and the setting of the carry flag from the contents of the accumulator. The
result is stored in the accumulator. SBB then updates the setting of the carry flag to indicate the outcome of
the operation

SBB's use of he carry flag enables the program to subtract nulti-byte strings. SBB incorporates the carry flag by
adding it to tile byte to be subtracted from the accumulator. It then subtracts the result from the accumulator
by using two', complement addition. These preliminary operations occur in the processor's internal work registers
so that the SOJrce data remains unchanged.

Subtract Regl.'ter from Accumulator with Borrow

Opcode Operand

SBB reg

The operand nust specify one of the registers A through E, H or L. This instruction subtracts the contents of
the specified I egister and the carry flag from the accumulator and stores the result in the accumulator.

11 0 0 S 5 S I
Cycles: 1
States: 4
Flags: Z,S,P,CY,AC

3-56


Subtract Memory from Accumulator with Borrow

Opcode Operand

SBB M

This instruction subtracts the carry flag and the contents of the memory location addressed by the Hand L
registers from the accumulator and stores the result in the accumulator.

Cycles: 2
States: 7
Flags: Z,S,P,CY,AC

Example:

Assume that register B contains 2, the accumulator contains 4, and the carry flag is set to 1. The instruction
SBB B operates as follows:

2H + carry = 3H
2's complement of 3H = 11111101

Accumulator = 00000100
11111101
00000001 = 1H
Notice that this two's complement addition produces a carry. When SBB complements the carry bit generated
by the addition, the carry flag is reset OFF. The flag settings resulting from the SBB B instruction are as
follows:

Carry o
Sign o
Zero o
Parity o
Aux. Carry 1

SBI SUBTRACT IMMEDIATE WITH BORROW

SBI subtracts the contents of the second Instruction byte and the setting of the carry flag from the contents of
the accumulator. The result is stored in the accumulator.

SBI's use of the carry flag enables the program to subtract multi-byte strings. SBI incorporates the carry flag by
adding it to the byte to be subtracted from the accumulator. It then subtracts the result from the accumulator
by using two's complement addition. These preliminary operations occur In the processor's internal work registers
so that the immediate source data remains unchanged.

3-57


The assembler s relocation feature treats all external and relocatable symbols as 16-bit addresses. When one of
HIGH or LOlA operator to specify which byte of the address is to be used in the evaluation of the expression.
When neither cJperator is present, the assembler assumes the LOW operator and issues an error message.

Opcode Operand

5BI data

The operand must specify the data to be subtracted. This data may be in the form of a number, an ASCII
constant, the Iabel of some perviously defined value, or an expression. The data may not exceed one byte.

o 01
Cycles: 2
States: 7
Flags: Z,5,P,CY.AC

Example:

The following sequence of instructions enables the program to test the setting of the carry flag:

XRA A
5BI 1

The exclusive OR with the accumulator clears the accumulator to zeros but does not affect the setting of the
carry flag. (Tfe XRA instruction is explained later in this chapter.) When the carry flag is OFF, 5BI 1 yields
a minUS one. Nhen the flag is set ON, 5BI 1 yields a minus two.

NOTE

This example is included for illustrative purposes. In most
cases, the carry flag can be tested more efficiently by using
the JNC instruction (jump if no carry).

SHLD STORE HAND L DIRECT

5HLD stores l copy of the L register in the memory location specified in bytes two and three of the SHLD
Instruction. 5-lLD then stores a copy of the H register in the next higher memory location.

Opcode Operand

SHLD address

The address may be stated as a number, a previously defined label. or an expression.

3·58


SHLD is one of the instructions provided for saving the contents of the Hand L registers. Alternately, the H
and L data can be placed in the D and E registers (XCHG instruction) or placed on the stack (PUSH and XTHL
instructions).

0 0 1 0 0 0 1 0

lowaddr

high addr

Cycles: 5
States: 16
Addressing: direct
Flags: none

Example:

Assume that the Hand L registers contain OAEH and 29H, respectively, The following is an illustration of the
effect of the SHLD lOAH instruction:

MEMORY ADDRESS

109 lOA lOB 10C
Memory Before SHLD 00 00 00 00
Memory After SH LD 00 29 AE 00

SIM (8085 PROCESSOR ONLY) SET INTERRUPT MASK

SI M is a multi-purpose instruction that uses the current contents of the accumulator to perform the following
functions: Set the interrupt mask for the 8085's RST5.5, RST6.5, and RST7.5 hardware interrupts: reset
RST7.5's edge sensitive input; and output bit 7 of the accumulator to the Serial Output Data latch.

Opcode Operand

SIM

Operands are not permitted with the SIM instruction. However, you must be certain to load the desired bit
configurations into the accumulator before executing the SIM instruction. SIM interprets the bits in the accumu-
lator as follows:

]-59


o = available
{ 1 = masked

ignored
If 1, bit 7 is output to Serial Output Data Latch
Serial Output Data: ignored if bit 6 = 0

Accumulator :,its 3 and 6 function as enable switches. If bit 3 IS set ON (set to 1), the set mask function is
enabled. Bits (J through 2 then mask or leave available the corresponding RST interrupt. A 1 bit masks the
interrupt mak ng It unavailable; a 0 bit leaves the interrupt available. If bit 3 is set OFF (reset to 0), bits 0
through 2 hav~ no effect. Use this option when you want to send a serial output bit without affecting the
interrupt mas!..

Notice that the DI (Disable Interrupts) instruction overrides the SIM instruction. Whether masked or not, RST5.5,
RST6.5, and IlST7.5 are disabled when the DI instruction IS in effect. Use the RIM (Read Interrupt Mask)
instruction to determine the current settings of the interrupt flag and the interrupt masks.

If bit 6 is set to 1, the serial output data function is enabled. The processor latches accumulator bit 7 into the
SOD output v'here it can be accessed by a peripheral device. If bit 6 IS reset to 0, bit 7 IS ignored.

A 1 in accumiJlator bit 4 resets OFF the RST7.5 input flip flop. Unlike RST5.5 and 6.5, RST7.5 IS sensed via a
processor flip flop that is set when a peripheral device Issues a pulse with a rising edge. This edge triggered Input
supports devices that cannot maintain an interrupt request until serviced. RST7.5 is also useful when a device
does not requ re any explicit hardware service for each interrupt. For example, the program might increment and
test an event ,:ounter for each interrupt rather than service the device directly.

The RST7.5 f ip flop remains set until reset by 1) Issuing a RESET to the 8085, 2) recognizing the interrupt, or
3) setting accLmulator bit 4 and executing a SIM instruction. The Reset RST7.5 feature of the SIM instruction
allows the pre gram to override the interrupt.

The RST7.5 Illput flip flop is not affected by the setting of the interrupt mask or the DI instruction and there-
fore can be set at any time. However, the interrupt cannot be serviced when RST7.5 is masked or a DI instruction
is in effect.

0 0 0 0 0 01
1

Cycles: 1
States: 4
Flags: none

Example 1: <ssume that the accumulator contains the bit pattern 00011100. The SIM instruction resets the
RST7.5 flip fl)p and sets the RST7.5 interrupt mask. If an RSn.5 interrupt is pending when this SIM instruction
is executed, it is overridden without being serviced. Also, any subsequent RST7.5 Interrupt is masked and cannot
be serviced urtil the interrupt mask is reset.

3-60


Example 2: Assume that the accumulator contains the bit pattern 11001111. The 51 M instruction masks out the
R5T5.5, R5T6.5, and R5T7.5 level interrupts and latches a 1 bit into the SOD input. By contrast, the bit pattern
10000111 has no effect since the enable bits 3 and 6 are not set to ones.

SPHL MOVE H&L TO SP

5PHL loads the contents of the Hand L registers into the SP (Stack Pointer) register.

Opcode Operand

SPHL

Operands are not permitted with the SPHL instruction.

SP is a special purpose 16·bit register used to address the stack; the stack must be in random access memory
(RAM). Because different applications use different memory configurations, the user program must load the SP
register with the stack's beginning address. The stack is usually assigned to the highest available location in RAM.
The hardware decrements the stack pointer as items are added to the stack and increments the pointer as items
are removed.

The stack pointer must be initialized before any instruction attempts to access the stack. Typically, stack
initialization occurs very early in the program. Once established, the stack pointer should be altered with
caution. Arbitrary use of 5PHL can cause the loss of stack data.

Cycles: 1
States: 5 (6 on 8085)
Flags: none

Example:

Assume that the Hand L registers contain SOH and OFFH, respectively. SPHL loads the stack pointer with the
value 50FFH.

STA STORE ACCUMULATOR DIRECT

STA stores a copy of the current accumulator contents into the memory location specified in bytes two and
three of the STA instruction.

Opcode Operand

STA address

The address may be stated as a number, a previously defined label, or an expression. The assembler inverts the
high and low address bytes when it builds the instruction.

3-61

Chapter 3. Instruction Se.

0 0 1 1 0 0 1 0

lowaddr

high addr

Cycles: 4
States: 13
Addressing: direct
Flags: none

Example:

The following instruction stores a copy of the contents of the accumulator at memory location SB3H:

STA SB3H

When assembl( d. the previous instruction has the hexadecimal value 32 B3 05. Notice that the assembler inverts
the high and I'lw order address bytes for proper storage in memory.

STAX STORE ACCUMULATOR INDIRECT

The STAX ins :ruction stores a copy of the contents of the accumulator into the memory location addressed
by register pai B or register pair D.

Opcode Operand

STAX

The operand E specifies the Band C register pair; D specifies the D and E register pair. This instruction may
specify only tie B or D register pair.

10 0 oeJo '-...,-/
0 01

IfII 0 = register pair B
= register pair D

CYcles: 2
States: 7
Flags: none

Example:

If register B c<.ntains 3FH and register C contains 16H. the following instruction stores a copy of the contents
of the accumuiator at memory location 3F16H:

STAX B
3-62


STC SET CARRY

STC sets the carry flag to one. No other flags are affected.

Opcode Operand

STC

Operands are not permitted with the STC instruction.

10 0 o
Cycles: 1
States: 4
Flags: CY

When used in combination with the rotate accumulator through the carry flag instructions, STC allows the pro-
gram to modify individual bits.

SUB SUBTRACT

The SUB instruction subtracts one byte of data from the contents of the accumulator. The result IS stored in the
accumulator, SUB uses two's complement representation of data as explained in Chapter 2. Notice that the SUB
Instruction excludes the carry flag (actually a 'borrow' flag for the purposes of subtraction) but sets the flag to
indicate the outcome of the operation.

Subtract Register from Accumulator

Opcode Operand

SUB reg

The operands must specify one of the registers A through E, H or L. The instruction subtracts the contents of
the specified register from the contents of the accumulator using two's complement data representation. The
result is stored in the accumulator,

oIss S I
Cycles: 1
States: 4
Flags: Z.S,P,CY,AC

Subtract Memory from Accumulator

Opcode Operand

SUB M

3-63


This instruction subtracts the contents of the memory location addressed by the Hand L registers from the
contents of th ~ accumulator and stores the result in the accumulator. M is a symbolic reference to the Hand L
registers.

o 01
Cycles: 2
States: 7
Flags: Z,S,P,CY,AC

Example:

Assume that tne accumulator contains 3EH. The instruction SUB A subtracts the contents of the accumulator
from the accumulator and produces a result of zero as follows:

3EH 00111110
+(-3EH) 11000001 one's complement
1 add one to produce two's complement
carry out =1 00000000 result = 0

The conditior flags are set as follows:

Carry 0
Sign 0
Zero 1
Parity 1
Aux. Carry 1

Notice that the SUB instruction complements the carry generated by the two's complement addition to form a
'borrow' flag. The auxiliary carry flag is set because the particular value used in this example causes a carry out
of bit 3.

SUI SUBTRACT IMMEDIATE

SU I subtracts the contents of the second instruction byte from the contents of the accumulator and stores the
result in the •.ccumulator. Notice that the SUI instruction disregards the carry ('borrow') flag during the sub-
traction but ,ets the flag to Indicate the outcome ofthe operation.

Opcode Operand

SUI data

The operand must specify the data to be subtracted. This data may be in the form of a number, an ASCII
constant, the label of some previously defined value, or an expression. The data must not exceed one byte.

The assemble "s relocation feature treats all external and relocatable symbols as 16-bit addresses. When one of
these symbol. appears in the operand expression of an immediate instruction, it must be preceded by either the

3-64



a a 01
Cycles: 2
States: 7
Flags: Z,S,P,CY,AC

Example:

Assume that the accumulator contains the value 9 when the instruction SUI 1 is executed:

Accumulator 00001001 = 9H
Immediate data (2's comp) 11111111 = -1 H

00001000 = 8H

Notice that this two's complement addition results in a carry, The SUI instruction complements the carry
generated by the addition to form a 'borrow' flag. The flag settings resulting from this operation are as follows:

Carry a
Sign a
Zero a
Parity a
Aux. Carry 1

XCHG EXCHANGE HAND L WITH D AND E

XCHG exchanges the contents of the Hand L registers with the contents of the D and E registers.

Opcode Operand

XCHG

Operands are not allowed with the XCHG instruction.

XCHG both saves the current Hand L and loads a new address into the Hand L registers. Since XCHG is a
register-to-register instruction, it provides the quickest means of saving and/or altering the Hand L registers.

a a
Cycles: 1
States: 4
Flags: none

3-65


Example:

Assume that the Hand L registers contain 1234H, and the D and E registers contain OABCDH. Following
execution of tre XCHG instruction, Hand L contain OABCDH, and D and E contain 1234H.

XRA EXCLUSIVE OR WITH ACCUMULATOR

XRA performs an exclusive OR logical operation using the contents of the specified byte and the accumulator,
The result IS pi Iced in the accumulator,

Summary of Lugical Operations

AND produces a one bit in the result only when the corresponding bits in the test data and the mask data are
ones.

OR produces a one bit in the result when the corresponding bits In either the test data or the mask data are
ones.

different; i.e., 2 one bit in either the test data or the mask data - but not both - produces a one bit in the
resul t.

AND OR EXCLUSIVE OR

1010 1010 1010 1010 1010 1010
0000 1111 0000 1111 0000 1111
0000 1010 10101111 1010 0101

XRA Register ,lith Accumulator

Opcode Operand

XRA reg

The operand mJst specify one of the registers A through E, H or L. This instruction performs an exclUSive OR
using the contelts of the specified register and the accumulator and stores the result In the accumulator. The
carry and auxil ary carry flags are reset to zero.

a a S S S

Cycles: 1
States: 4
AddreSSing: register
Flags: Z,S,P,CY,AC

3-66


XRA Memory with Accumulator

Opcode Operand

XRA M

The contents of the memory location specified by the Hand L registers is exclusive-ORed with the contents of
the accumulator. The result is stored in the accumulator. The carry and auxiliary carry flags are reset to zero.

o o o,
Cycles: 2
States: 7
Flags: Z,S,P,CY,AC

Examples:

Since any bit exclusive-0Red with itself produces zero, XRA is frequently used to zero the accumulator. The
following instructions zero the accumulator and the Band C registers.

XRA A
MOV B,A
MOV C,A

Any bit exclusive-ORed with a one bit is complemented. Thus, if the accumulator contains all ones (OFFH),
the instruction XRA B produces the one's complement of the B register in the accumulator.

XRI EXCLUSIVE OR IMMEDIATE WITH ACCUMULATOR

XRI performs an exclusive OR operation using the contents of the second instruction byte and the contents of
the accumulator. The result is placed in the accumulator. XRI also resets the carry and auxiliary carry flags to
zero.

Opcode Operand

XRI data

The operand must specify the data to be used in the OR operation. This data may be in the form of a number,
an ASCII constant, the label of some previously defined value, or an expression. The data may not exceed one
byte.

When neither operator IS present, the assembler assumes the LOW operator and issues an error message.

3-67

Chapter 3. Instruction Se',

o o
data

Cycles: 2
States: 7
Flags: Z,S,P,CY,AC

Summary of LJgica/ Operations

AND produce~ a one bit in the result only when the corresponding bits in the test data and the mask data are
ones.

OR produces, one bit in the result when the corresponding bits in either the test data or the mask data are
ones.

Exclusive OR Jroduces a one bit only when the corresponding bits in the test data and the mask data are
different; i.e., a one bit in either the test data or the mask data - but not both - produces a one bit in the
result.

AND OR EXCLUSIVE OR

1010 1010 1010 1010 1010 1010
0000 1111 0000 1111 0000 1111
00001010 1010 1111 1010 0101

Example:

Assume that a program uses bits 7 and 6 of a byte as flags that control the calling of two subroutines. The
program tests the bits by rotating the contents of the accumulator until the desired bit is in the carry flag; a
CC instructior (Call if Carry) tests the flag and calls the subroutine if required.

Assume that tle control flag byte is positioned normally In the accumulator, and the program must set OFF bit
6 and set bit " ON. The remaining bits, which are status flags used for other purposes, must not be altered.
Since any bit ~xclusive-ORed with a one is complemented, and any bit exclusive-oRed with a zero remains
unchanged, th~ following Instruction is used:

XRI 110000008

The Instruction has the follOWing results:

Immediate data 11000000
10001100

3-68


XTHL EXCHANGE H&L WITH TOP OF STACK

XTHL exchanges two bytes from the top of the stack with the two bytes stored in the Hand L registers. Thus,
XTHL both saves the current contents of the Hand L registers and loads new values into Hand L.

Opcode Operand

XTHL

Operands are not allowed with the XTHL instruction.

XTHL exchanges the contents of the L register with the contents of the memory location specified by the SP
(Stack Pointer) register. The contents of the H register are exchanged with the contents of SP+ 1.

000 1 I
Cycles: 5
States: 18 (16 on 8085)
Flags: none

Example: •

Assume that the stack pOinter register contains 10ADH; register H contains OBH and L contains 3CH; and
memory locations 10ADH and 10AEH contain FOH and ODH, respectively. The following is an illustration of
the effect of the XTHL instruction:

MEMORY ADDRESS H L
lOAC lOAD 10AE lOAF

Before XTHL FF Fa aD FF OB 3C
After XTHL FF 3C OB FF aD Fa

The stack pointer register remains unchanged following execution of the XTHL instruction.

3~9

4. ASSEMBLER DIRECTIVES

This chapter describes the assembler directives used to control the 8080/85 assembler in its generation of object
code. This chapter excludes the macro directives, which are discussed as a separate topic in Chapter 5.

Generally, directives have the same format as instructions and can be interspersed throughout your program.
Assembler directives discussed in this chapter are grouped as follows:

GENERAL DIRECTIVES:

• Symbol Definition

EQU
SET

• Data Definition

DB
DW

• Memory Reservation

DS

• Conditional Assembly

IF
ELSE
ENDIF

• Assembler Termination

END

LOCATION COUNTER CONTROL AND RELOCATION:

• Location Counter Control

ASEG
DSEG
CSEG
ORG

• Program Linkage

PUBLIC
EXTRN
NAME
STKLN
4-1

Chapter 4. Assembler Oir ,ctives

Three assembl" directives - EQU, SET, and MACRO - have a slightly different format from assembly
language instnlctions. The EQU, SET. and MACRO directives require a name for the symbol or macro being
defined to be present in the label field. Names differ from labels in that they must not be terminated with a
colon (:) as laJels are. Also, the LOCAL and ENDM directives prohibit the use of the label field.

The MACRO, ENDM, and LOCAL directives are explained in Chapter 5.

SYMBOL DEFINITION

The assembler automatically assigns values to symbols that appear as instruction labels. This value IS the current
setting of the location counter when the instruction IS assembled. (The location counters are explained under
'Address Cont'ol and Relocation,' later in this chapter.)

You may defile other symbols and assign them values by using the EQU and SET directives. Symbols defined
using EQU callnot be redefined during assembly; those defined by SET can be assigned new values by subsequent
SET directive~.

The name req Jired in the label field of an EQU or SET directive must not be terminated with a colon.

Symbols defined by EQU and SET have meaning throughout the remainder of the program. This may cause the
symbol to have illegal multiple definitions when the EQU or SET directive appears in a macro definition. Use
the LOCAL d rective (described in Chapter 5) to avoid this problem.

EQU Directive

EQU assigns t le value of 'expression' to the name specified in the label field.


name EQU expression

The required lame in the label field may not be terminated with a colon. This name cannot be redefined by a
subsequent EOU or SET directive. The EQU expression cannot contain any external symbol. (External symbols
are explained under 'Location Counter Control and Relocation,' later in this chapter.)

Assembly-tim! evaluation of EQU expressions always generates a modulo 64K address. Thus, the expression
always yields 1 value in the range 0-65,536.

Example:

The following EQU directive enters the name ONES into the symbol table and assigns the binary value
11111111 to t:

ONES EQU OFFH

4-2

Chapter 4. Assembler Directives

The value assigned by the EQU directive can be recalled in subsequent source lines by referring to its assigned
name as in the following IF directive:

IF TYPE EQ ONES

ENDIF

SET Directive

SET assigns the value of 'expression' to the name specified in the label field.


name SET expression

The assembler enters the value of 'expression' into the symbol table. Whenever 'name' is encountered sub-
sequently in the assembly, the assembler substitutes its value from the symbol table. This value remains unchanged
until altered by a subsequent SET directive.

The function of the SET directive is identical to EQU except that 'name' can appear in multiple SET directives
in the same program. Therefore, you can alter the value assigned to 'name' throughout the assembly.

Assembly-time evaluation of SET expressions always generates a modulo 64K address. Thus, the expression
always yields a value in the range 0-65,536.

Examples:

Label Opcode Operand Assembled Code

IMMED SET 5
ADI IMMED C605

IMMED SET lOH-6
ADI IMMED C60A

DATA DEFINITION

The DB (define byte) and DW (define word) directives enable you to define data to be stored in your program.
Data can be specified in the form of 8-bit or 16-bit values, or as a string of text characters.

DB Directive

The DB directive stores the specified data in consecutive memory locations starting with the current setting of the
location counter.

4-3

Chapter 4. Assembler Oi, ectives

Label Opcode Operands

optional: DB expresslon(s) or string(s)

The operand 'ield of the DB directive can contain a list of expressions and/or text strings. The list can contain
up to eight tc tal items: list items must be separated by commas. Because of limited workspace, the assembler
may not be a Jle to handle a total of eight items when the list includes a number of complex expressions. If
you ever haVE this problem, it is easily solved: simply use two or more directives to shorten the list.

Expressions nlust evaluate to l-byte (8-bit) numbers in the range -256 through 255. Text strings may comprise
a maximum of 128 ASCII characters enclosed in quotes.

The assemble,'s relocation feature treats all external and relocatable symbols as 16-bit addresses. When one of
these symbol~ appears in an operand expression of the DB directive, it must be preceded by either the HIGH or
LOW operato' to specify which byte of the address is to be used in the evaluation of the expression. When
neither opera .or is present, the assembler assumes the LOW operator and issues an error message.

If the option;.! label IS present, it is assigned the starting value of the location counter, and thus references
the first byte stored by the DB directive. Therefore, the label STR in the following examples refers to the letter
T of the stmg TIME.

Examples:

Label Opcode Operands Assembled Code

STR: DB 'TIME' 54494D45

HERE: DB OA3H A3

WORD1: DB -03H,5*2 FDOA

DW Directive

The DW direl tlve stores each 16-blt value from the expression list as an address. The values are stored starting
at the curren setting of the location counter.


optional: DW expression list

The least sigr ificant eight bits of the first value in the expression list are stored at the current setting of the
location cour ter: the most significant eight bits are stored at the next higher location. This process is repeated
for each item in the expression list.

Expressions E valuate to 1-word (16-bit) numbers, typically addresses. If an expression evaluates to a single byte,
it IS assumed to be the low order byte of a 16-bit word where the high order byte is all zeros.

44


List items must be separated by commas. The list can contain up to eight total items. Because of limited work-
space, the assembler may not be able to handle eight complex expressions. If you ever have this problem, simply
use two or more OW directives to shorten the list.

The reversed order for storing the high and low order bytes is the typical format for addresses stored in memory.
Thus, the OW directive is commonly used for storing address constants.

Strings containing one or two ASCII characters enclosed in quotation marks may also appear in the expression
list. When using such strings in your program, remember that the characters are stored in reversed order.
Specifying a string longer than two characters causes an error.

If the optional label is present, it is assigned the starting address of the location counter, and thus references the
first byte stored by the OW directive. (This is the low order byte of the first Item in the expression list.)

Examples:

Assume that COMP and FI LL are labels defined elsewhere in the program. COMP addresses memory location
3B1CH. FILL addresses memory location 3EB4H.

Label Opcode Operands Assembled Code

AOOR1: OW COMP lC3B

AOOR2: OW FILL B43E

STRNG: OW 'A','AB' 41004241

FOUR: OW 4H 0400

MEMORY RESERVATION

OS Directive

The OS directive can be used to define a block of storage.


optional: OS expression

The value of 'expression' specifies the number of bytes to be reserved for data storage. In theory, this value may
range from OOH through OFFFFH; in practice. you will reserve no more storage than will fit in your available
memory and still leave room for the program.

Any symbol appearing in the operand expression must be defined before the assembler reaches the OS directive.

Unlike the OB and OW directives, OS assembles no data into your program. The contents of the reserved storage
are unpredictable when program execution is initiated.

4-5

Chapter 4. Assembler Dir 'ctives

If the optlona label is present, it is assigned the current value of the location counter, and thus references the
first byte of tle reserved memory block.

If the value 01 the operand expression is zero, no memory is reserved. However, if the optional label is present,
it is assigned 1he current value of the location counter.

The DS directve reserves memory by Incrementing the location counter by the value of the operand expression.

Example:

TTYBUF: DS 72 ;RESERVE 72 BYTES FOR
;A TERMINAL OUTPUT BUFFER

Programming Tips: Data Description and Access

Random Access lersus Read Only Memory

When coding data descriptions, keep in mind the mix of ROM and RAM in your application.

Generally, the DB and DW directives define constants, Items that can be assigned to ROM. You can use these
items In your program, but you cannot modify them. If these items are assigned to RAM, they have an initial
value that YOL r program can modify during execution. Notice, however, that these initial values must be reloaded
Into memory Jrior to each execution of the program.

Variable data n memory must be assigned to RAM.

Data Description

Before coding your program, you must have a thorough understanding of ItS input and output data. But you'll
probably find it more convenient to postpone coding the data descriptions until the remainder of the program is
fairly well deeloped. This way you will have a better idea of the constants and workareas needed In your program.
Also, the orgalization of a typical program places Instructions in lower memory, followed by the data, followed
by the stack.

Data Access

Accessing dati from memory is typically a two·step process: First you tell the processor where to find the data,
then the processor fetches the data from memory and loads it into a register, usually the accumulator. Therefore,
the following ;ode sequences have the identical effect of loading the ASCII character A into the accumulator.

AAA: DB 'A' ALPHA: DB 'ABC'

LXI B,AAA LXI B,ALPHA
LDAX B LDAX B

4-6


In the examples, the LXI instructions load the address of the desired data into the Band C registers. The LDAX
instructions then load the accumulator with one byte of data from the address specified in the Band C registers.
The assembler neither knows nor cares that only one character from the three-character field ALPHA has been
accessed. The program must account for the characters at ALPHA+1 and ALPHA+2, as in the following coding
sequence:

ALPHA: DB 'ABC' ;DEFINE ALPHA

LXI B,ALPHA ;LOAD ADDRESS OF ALPHA
LDAX B ;FETCH 1ST ALPHA CHAR

INX B ;SET B TO ALPHA+l
LDAX B ;FETCH 2ND ALPHA CHAR

INX B ;SET B TO ALPHA+2
LDAX B ;FETCH 3RD ALPHA CHAR

The coding above is acceptable for short data fields like ALPHA. For longer fields, you can conserve memory
by setting up an instruction sequence that is executed repeatedly until the source data is exhausted.

Add Symbols for Data Access

The following example was presented earlier as an illustration of the DS directive:


TTYBUF: DS 72 ;RESERVE TTY BUFFER

To access data in this buffer using only expressions such as TTYBUF+l, TTYBUF+2, ... TTYBUF+72 can be
a laborious and confusing chore, especially when you want only selected fields from the buffer. You can simplify
this task by subdivid.ing the buffer with the EQU directive:


TTYBUF: DS 72 ;RESERVE TTY BUFFER

ID EQU TTYBUF ;RECORD IDENTIFIER

NAME EQU TTYBUF+6 ;20-CHAR NAME FIELD

NUMBER EQU TTYBUF+26 ;10-CHAR EMPLOYEE NUMBER

DEPT EQU TTYBUF+36 ;5-CHAR DEPARTMENT NUMBER

SSNO EQU TTYBUF+41 ;SOCIAL SEC. NUMBER

DOH EQU TTYBUF+50 ;DATE OF HIRE

DESC EQU TTYBUF+56 ;)OB DESCRIPTION

4-7

Chapter 4. Assembler Dir'ctives

Subdividing d. ta as shown in the example simplifies data access and provides useful documentation throughout
your program. Notice that these EQU directives can be inserted anywhere within the program as you need them,
but coding tht m as shown in the example provides a more useful record description.

CONDITIONAL ASSEMBLY

The IF. ELSE. and ENDIF directives enable you to assemble portions of your program conditionally, that is,
only if certain conditions that you specify are satisfied.

Conditional a~sembly is especially useful when your application requires custom programs for a number of com-
mon options. As an example, assume that a basic control program requires customlz'ing to accept input from
one of six dif erent sensing devices and to drive one of five different control dev,ices. Rather than code some
!
thirty separat" programs to account for all the possibilities, you can code a single program. The code for the in-
dividual senso's and drivers must be enclosed by the conditional directives. When you need to generate a custom
program, you can insert SET directives near the beginning of the source program to select the desired sensor and
driver routine ..

IF, ELSE. ENDIF [irectives

Because these directives are used in conjunction. they are described together here.


optional: IF expression

optional: ELSE

optional: ENDIF

The assembler evaluates the expression in the operand field of the IF directive. If bit 0 of the resulting value is
one (TRUE), til Instructions between the IF directive and the next ELSE or ENDIF directive are assembled.
When bit 0 is zero (FALSE) these instructions are ignored. (A TRUE expression evaluates to OFFFFH and
FALSE to OH: only bit zero need be tested.)

All statement~ included between an IF directive and its required associated ENDIF directive are defined as an
IF-ENDIF blo;k. The ELSE directive is optional, and only one ELSE directive may appear In an IF-ENDIF
block. When i lcluded. ELSE is the converse of IF. When bit 0 of the expression in the IF directive IS zero, all
statements be:ween ELSE and the next ENDIF are assembled. If bit 0 IS one. these statements are ignored.

Operands are lOt allowed with the ELSE and ENDIF directives.

An IF-ENDIF block may appear within another IF-ENDIF block. These blocks can be nested to eight levels.

Macro definitions (explained in the next chapter) may appear within an IF-ENDIF block. Conversely, IF-ENDIF
blocks may al'pear within macro definitions. In either case, you must be certain to terminate the macro definition

4-8


or IF-ENDIF block so that it can be assembled completely, For example, when a macro definition begins In an
IF block but terminates after an ELSE directive, only a portion of the macro can be assembled. Similarly, an
IF-ENDIF block begun within a macro definition must terminate within that same macro definition.

NOTE

Caution IS required when symbols are defined in IF-ENDIF
blocks and referenced elsewhere within the program. These
symbols are undefined when the evaluation of the IF ex-
pression suppresses the assembly of the IF-ENDIF block.

Example 1. Simple IF-ENDIF Block:

CONDl IF TYPE EQ 0

;ASSEMBLED IF 'TYPE = 0'
;IS TRUE

ENDIF

Example 2. IF-ELSE-ENDIF Block:

COND2: IF TYPE EQ 0
;IS TRUE

ELSE

:IS FALSE

ENDIF

4-9


Example 3. Nested IF's:

COt ID3: IF TYPE EO 0

;15 TRUE

IF MODE EO 1

LE'EL ;ASSEMBLED IF 'TYPE = 0'
1 ;AND 'MODE = l' ARE BOTH
;TRUE
ENDIF
ELSE

LEVEL ;ASSEMBLED IF 'TYPE = 0'
2 ;15 FALSE

IF MODE EO 2

;15 FALSE AND 'MODE = 2'
;15 TRUE
LEEL ELSE
1
;AND 'MODE = 2' ARE BOTH
;FALSE
ENDIF
ENDIF

ASSEMBLER TERMINATION

END Directive

The END dir~ctlve identifies the end of the source program and terminates each pass of the assembler.


optional: END expression

Only one END statement may appear in a source program, and it must be the last source statement.

If the optioml expression is present, its value is used as the starting address for program execution. If no ex-
pression is gi len, the assembler assumes zero as the starting address.

When a number of separate program modules are to be joined together, only one may specify a program starting
address. The module with a starting address is the main module. When source files are combined using the IN-
CLUDE cont'ol, there are no restrictions on which source file contains the END.

4-10


END-OF-TAPE INDICATION

The EOT directive allows you to specify the physical end of paper tape to simplify assembly of multiple-tape source
programs.

EOT Directive


optional: EOT

When EOT is recognized by the assembler, the message 'NEXT TAPE' is sent to the console and the assembler pauses.'
After the next tape is loaded, a 'space bar' character received at the console signals continuation of the assembly.

Data in the operand field causes an error.

LOCATION COUNTER CONTROL AND RELOCATION

All the directives discussed in the remainder of this chapter relate directly to program relocation except for the
ASEG and ORG directives. These directives are described first for the convenience of readers who do not use the
relocation feature.

Location Counter Control (Non-Relocatable Mode)

When you elect not to use the relocation feature, an assembler default generates an ASEG directive for you. The
ASEG directive specifies that the program is to be assembled in the non-relocatable mode and establishes a
location counter for the assembly.

The location counter performs the same function for the assembler as the program counter performs during
execution. It tells the assembler the next memory location available for instruction or data assembly.

Initially, the location counter is set to zero. The location counter can be altered by the ORG (origin) directive.

ORG Directive

The ORG directive sets the location counter to the value specified by the operand expression.


optional: ORG expression

The location counter is set to the value of the operand expression. Assembly-time evaluation of ORG expressions
always Yields a modulo 64K address. Thus, the expression always yields an address in the range 0 through
65,535. Any symbol In the expression must be preViously defined. The next machine instruction or data item is
assembled at the specified address.

4-11

Chapter 4. Assembler Oi 'ectives

If no ORG di 'ective is included before the first instruction or data byte in your program, assembly begins at
location zero.

Your prograrr can include any number of ORG directives. Multiple ORG's need not specify addresses In
ascending seq Jence, but if you fail to do so, you may instruct the assembler to write over some previously
assembled POI tion of the program.

If the option" label is present, it is assigned the current value of the location counter before it is updated by the
ORG directiv".

Example:

Assume that the current value of the location counter is OFH (decimal 15) when the following ORG directive is
encountered:

ORG OFFH ;ORG ASSEMBLER TO LOCATION

;OFFH (decimal 225)

The symbol FAG1 is assigned the address OFH. The next instruction or data byte is assembled at location
OFFH.

Introduction to Reocatability

A maior feature of this assembler is its system for creating relocatable object code modules. Support for this new
feature includes a number of new directives for the assembler and three new programs included in ISIS-II. The
three new pr<lgrams - LIB, LINK, and LOCATE - are described in the ISIS-II System User's Guide. The new
assembler dir ~ctives are described later in this chapter.

Relocatabilit, allows the programmer to code programs or sections of programs without worrying about the
final arrangerlent of the object code in memory. This offers developers of microcomputer systems malor ad-
vantages In t",o areas: memory management and modular program development.

Memory ManagEment

When developing, testing, and debugging a system on your Intellec microcomputer development system, your
only concern with locating a program is that it doesn't overlap the resident routines of 1515·11. Because the
Intellec syste 11 has 32K, 48K, or 64K of random access memory, the location of your future program is not a
great concerr. However, the program you are developing will almost certainly use some mix of random access
memory (RAM), read-only memory (ROM), andior programmable read-only memory (PROM). Therefore, the
location of y)ur program affects both cost and performance in your application. The relocatability feature allows
you to deveillp, test, and debug your program on the Intellec development system and then simply relocate the
object code 10 suit your application.

The relocatal dlity feature also has a malor advantage at assembly-time: often, large programs with many symbols
cannot be as,embled because of limited work space for the symbol table. Such a program can be divided Into a
number of rrodules that can be assembled separately and then linked together to form a single object program.

4-12


Modular Program Development

Although 'relocatability' may seem to be a formidable term, what it really means is that you can subdivide a
complex program into a number of smaller, simpler programs. This concept is best illustrated through the use of
an example. Assume that a microcomputer program IS to control the spark advance on an automobile engine.
This requires the program to sample the ambient air temperature, engine air intake temperature, coolant tempera-
ture, manifold vacuum, idle sensor, and throttle sensor.

Let us examine the approaches two different programmers might take to solve this problem. Both programmers
want to calculate the degree of spark advance or retardation that provides the best fuel economy with the lowest
emissions. Programmer A codes a single program that senses all inputs and calculates the correct spark advance.
Programmer B uses a modular approach and codes separate programs for each input plus one program to calculate
spark advance.

Although Programmer A avoids the need to learn to use the relocatability feature, the modular approach used
by Programmer B has a number of advantages you should consider:

• Simplified Program Development

It is generally easier to code, test, and debug several simple programs than one complex program.

• Sharing the Programming Task

If Programmer B finds that he is falling behind schedule, he can assign one or more of his sub-
programs to another programmer. Because of his single program concept, Programmer A will
probably have to complete the program himself.

• Ease of Testing

Programmer B can test and debug most of his modules as soon as they are assembled; Programmer
A must test his program as a whole. Notice that Programmer B has an extra advantage if the
sensors are being developed at the same time as the program. If one of the sensors is behind
schedule, Programmer B can continue developing and testing programs for the sensors that are
ready, Because Programmer A cannot test h is program until all the sensors are developed, his
testing schedule IS dependent on events beyond his control.

• Programming Changes

Given the nature of automotive design, it IS reasonable to expect some changes during system
development. If a change to one of the sensors requires a programming change, Programmer A
must search through his entire program to find and alter the coding for that sensor. Then he must
retest the entire program to be certain that those changes do not affect any of the other sensors.
By contrast, Programmer B need be concerned only with the module for that one sensor. This
advantage continues throughout the life of the program.

4-13


DIRECTIVES USED FOR RELOCATION

Several direc Ives have been added to the assembler to support the relocation feature. These fall into the general
categories of location counter control and program linkage.

Location Counter :ontrol (Relocatable Programs)

Relocatable Jrograms or program modules may use three location counters. The ASEG, DSEG, and CSEG
directives sp"cify which location counter is to be used.

The ASEG c irective specifies an absolute code segment. Even in a relocatable program module, you may want
to assign cer:ain code segments to specific addresses. For example, restart routines invoked by the RST instruc-
tion require specific addresses.

The CSEG c Ifective specifies a relocatable code segment. In general, the CSEG location counter is used for por-
tions of the program that are to be in some form of read-only memory, such as machine instructions and pro-
gram consta ltS.

The DSEG ocation counter specifies a relocatable data segment. This location counter is used for program
elements th It must be located In random access memory.

These direc ives allow you to control program segmentation at assembly time. The LOCATE program, described
In the ISIS-II System User's GUide, gives you control over program segment location. Therefore, the guidelines

given above are only general since they can be overridden by the LOCATE program.

Regardless 'If how many times the ASEG, CSEG, and DSEG directives appear in your program, the assembler
produces a ;ingle, contiguous module. This module comprISes four segments: code, data, stack and memory.
The LINK Ind LOCATE programs are used to combine segments from individual modules and relocate them in
memory. T lese programs are explained in the ISIS-II System User's Guide.

ASEG Directh'e

ASEG dire,;ts the assembler to use the location counter for the absolute program segment.


optional: ASEG

Operands ere not permitted with the ASEG directive.

All instrucions and data following the ASEG directive are assembled In the absolute mode. The ASEG directive
remains in effect until a CSEG or DSEG directive is encountered.

The ASEG location counter has an initial value of zero. The ORG directive can be used to assign a new value to
the ASEG location counter.

4-14


When assembly begins. the assembler assumes the ASEG directive to be in effect. Therefore. a CSEG or DSEG
must precede the first instruction or data definition in a relocatable module. If neither of these directives
appears in the program. the entire program is assembled in absolute mode and can be executed immediately
after assembly without using the LINK or LOCATE programs.

CSEG Directive

CSEG directs the assembler to assemble subsequent instructions and data In the relocatable mode uSing the code
segment location counter.

Labe! Opcode Operand

blank }
optional: CSEG PAGE
{ INPAGE

When a program contains multiple CSEG directives. all CSEG directives throughout the program must specify
the same operand. The operand of a CSEG directive has no effect on the current assembly. but is stored with
·the object code to be passed to the LINK and LOCATE programs. (These programs are described in the ISIS-II
System User's Guide.) The LOCATE program uses this information to determine relocation boundaries when it
joins this code segment to code segments from other programs. The meaning of the operand is as follows:

• blank - This code segment may be relocated to the next available byte boundary.

• PAGE - This code segment must begin on a page boundary when relocated. Page boundaries
occur in multiples of 256 bytes beginning with zero (0. 256. 512. etc.).

• INPAGE This code segment must fit within a single page when relocated.

The CSEG directive remains in effect until an ASEG or DSEG directive is encountered.

The code segment location counter has an initial value of zero. The ORG directive can be used to assign a new
value to the CSEG location counter.

DSEG Directive

DSEG directs the assembler to assemble subsequent instructions and data In the relocatable mode using the data
segment location counter.

Labe! Opcode Operand

optional: DSEG
roo'
PAGE
INPAGE)
i>
When multiple DSEG directives appear in a program. they must all specify the same operand throughout the
program. The operands for the DSEG directive have the same meaning as for the CSEG directive except that
they apply to the data segment.

4-15

Chapter 4. Assembler Dil ectives

There IS no ir teraction between the operands specified for the DSEG and CSEG directives. Thus. a code segment
can be byte r'locatable while the data segment is page relocatable.

The DSEG diective remains in effect until an ASEG or CSEG directive is encountered.

The data segr,lent location counter has an initial value of zero. The ORG directive can be used to assign a new
value to the [)SEG location counter.

ORG Directive ('?elocatable Mode)

The ORG dirxtive can be used to alter the value of the location counter presently in use.


optional: ORG expression

There are thr~e location counters. but only one location counter is in use at any given point in the program.
Which one dEpends on whether the ASEG. CSEG, or DSEG directive is in effect.

Any symboilised in the operand expression must have been previously defined. An exception causes phase
errors for all abels that follow the ORG and a label error if the undefined error is defined later.

When the O~ G directive appears in a relocatable program segment, the value of its operand expression must be
either absolu'e or relocatable within the current segment. Thus, if the ORG directive appears within a data seg-
ment, the val Je of its expression must be relocatable within the data segment. An error occurs if the expression
evaluates to , n address in the code segment.

If the option 11 label is present, It is assigned the current value of the location counter presently in use before
the ORG din ctive is executed.

Program Linkage [irectives

Modular pro! ramming and the relocation feature enable you to assemble and test a number of separate programs
that are to b; iOlned together and executed as a single program. Eventually, it becomes necessary for these
separate programs to communicate Information among themselves. Establishing such communication is the
function of the program linkage directives.

A program n,ay share its data addresses and instruction addresses with other programs. Only Items having an
entry in the iymbol table can be shared with other programs; therefore. the item must be assigned a name or a
label when it IS defined in the program. Items to be shared with other programs must be declared in a PUBLIC
directive.

Your prograln can directly access data or instructions defined In another program if you know the actual
address of tre item, but this is unlikely when both programs use relocation. Your program can also gain access
to data or Instructions declared as PUBLIC in other programs. Notice, however, that the assembler normally

4-16


flags as an error any reference to a name or label that has not been defined in your program. To avoid this,
you must provide the assembler with a list of items used in your program but defined in some other program.
These items must be declared in an EXTRN directive.

The two remaining program linkage directives, NAME and STKLN, are individually explained later in this chapter.

PUBLIC Directive

The PUBLIC directive makes each of the symbols listed in the operand field available for access by other programs.


optional: PUBLIC name-list

Each item in the operand name-list must be the name or label assigned to data or an instruction elsewhere in
this program. When multiple names appear in the list. they must be separated by commas. Each name may be
declared PUBLIC only once in a program module. Reserved words and external symbols (see the EXTRN
directive below) cannot be declared to be PUBLIC symbols.

PUBLIC directives may appear anywhere within a program module.

If an item in the operand name-list has no corresponding entry in· the symbol table (implying that it i5 unde-
fined), it is flagged as an error.

Example:

PUBLIC SIN,COS,TAN,SQRT

EXTRN Directive

The EXTRN directive provides the assembler with a list of symbols referenced in th is program but defined in a
different program. Because of this, the assembler establishes linkage to the other program and does not flag the
undefi ned references as errors.


optional: EXTRN name-list

Each item in the name-list identifies a symbol that may be referenced in this program butis defined in another
program. When multiple items appear in the list, they must be separated by commas.

If a symbol in the operand name-list is also defined in this program by the user, or is a reserved symbol. the effect
is the same as defining the same symbol more than once in a program. The assembler flags this error.

EXTRN directives may appear anywhere within a program module.

A symbol may be declared to be external only once in a program module. Symbols declared to be PUBLIC cannot
also be declared to be EXTRN symbols.

4·17

Chapter 4. Assembler Oi, ectives

If you omit a symbol from the name-list but reference it 111 the program, the symbol is undefined. The assembler
flags this erro', You may include symbols in the operand name-list that are not referenced in the program with-
out causing ail error.

Example:

EXTRN ENTRY,ADDRTN,BEGIN

NAME Directive

The NAME directive assigns a name to the object module generated by this assemblY,


optional: NAME module-name

The NAME directive requires the presence of a module-name in the operand field. This name must conform to
the rules for jefining symbols.

Module names are necessary so that you can refer to a module and specify the proper sequence of modules
when a numr er of modules are to be bound together.

The NAME directive must precede the first data or instruction coding in the source program, but may follow
comments anj control lines.

If the NAME directive is missing from the program, the assembler supplies a default NAME directive with the
module-name MODULE. This will cause an error if you attempt to bind together several object program
modules and more than one has the name MODULE. Also, if you make an error coding the NAME directive,
the default nime MODULE is assigned.

The module···name assigned by the NAME directive appears as part of the page heading in the assembly listing.

Example:

NAME MAIN

STKLN Directile

Regardless 01 the number of object program modules you may bind together, only one stack is generated. The
STKLN dire' tive allows you to specify the number of bytes to be reserved for the stack for each module.


optional: STKLN expression

The operand expression must evaluate to a number which will be used as the maximum size of the stack.

4-18


When the STKLN directive is omitted, the assembler provides a default STKLN of zero. This is useful when
multiple programs are bound together; only one stack will be generated, so only one program module need
specify the stack size. However, you should provide a STKLN if your module is to be tested separately and
uses the stack.

If your program includes more than one STKLN directive, only the last value assigned is retained.

Example:

STKLN 100

STACK and MEMORY Reserved Words

The reserved words STACK and MEMORY are not directives but are of interest to programmers using the
relocation feature. These reserved words are external references whose addresses are supplied by the LOCATE
program.

STACK is the symbolic reference to the stack origin address. You need this address to initialize the stack
pointer register. Also, you can base data structures on this address using svmbolic references such as STACK+1,
STACK+2, etc.

MEMORY is the symbolic reference to the first byte of unused memory past the end of your program. Again,
you can base data structures on this address using symbolic references such as MEMORY, MEMORY+l, etc.

Programming Tips: Testing Relocatable Modules

The ability to test individual program modules is a maior advantage of modular programming. However, many
program modules are not logically self-sufficient and require some modification before they can be tested. The
following is a discussion of some of the more common modifications that may be required.

Initialization Routines

In most complete programs, a number of housekeeping or initialization procedures are performed when execution
first begins. If the program module you are testing relies on initialization procedures aSSigned to a different
module, you must duplicate those procedures in the module to be tested. (Notice, however, that you can link
any number of modules together for testing.)

One of the most important initialization procedures is to set the stack pointer. The LOCATE program determines
the origin of the stack.

Your program should include the following instruction to initialize the stack pointer:

LXI SP,STACK

4-19

Chapter 4. Assembler [irectives

Input/Output

When testing ,rogram modules, it is likely that some input or output procedures appear in other modules. Your
program must simulate any of these procedures it needs to operate. Since your Intellec development system
probably has considerably more random access memory than you need to test a program module, you may be
able to simula:e Input and output data right in memory, The LOCATE program supplies an address for the
reserved word MEMORY; this is the address of the first byte of unused memory past the end of your program.
You can acces, this memory using the symbolic reference MEMORY, MEMORY+l, and so on. This memory
can be used fer storing test data or even for a program that generates test data.

Remove Coding Used for Testing

After testing ~our program, be certain to remove any code you inserted for testing. In particular, make certain
that only one module in the complete program initializes the stack pointer.

4-20

5. MACROS

INTRODUCTION TO MACROS

Why Use Macros?

A macro is essentially a facility for replacing one set of parameters with another. In developing your program,
you will frequently find that many Instruction sequences are repeated several times with only certain parameters
changed.

As an example, suppose that you code a routine that moves five bytes of data from one memory location to
another. A little later, you find yourself coding another routine to move four bytes from a different source
field to a different destination field. If the two routines use the same coding techniques, you will find that
they are identical except for three parameters: the character count, the source field starting address, and the
d:",tiiCatltl:' field starting address. Certainly It would be handy if there were some way to regenerate that original
'outine substituting the new parameters rather than rewrite that code yourself. The macro facility provides this
capability and offers several other advantages over writing code repetitiously'

e The tedium of frequent rewrite (and the probability of error) is reduced.

e Symbols used in macros can be restricted so that they have meaning only within the macro itself.
Therefore, as you code your program, you need not worry that you will accidentally duplicate a
symbol used in a macro. Also, a macro can be used any number of times in the same program
without duplicating any of its own symbols.

e An error detected In a macro need be corrected only once regardless of how many times the macro
appears in the program. This reduces debugging time.

e Duplication of effort between programmers can be reduced. Useful functions can be collected In a
library to allow macros to be copied into different programs.

In addition, macros can be used to improve program readability and to create structured programs. USing macros
to segment code blocks provides clear program notation and simplifies tracing the flow of the program.

What Is A Macro?

A macro can be described as a routine defined in a formal sequence of prototype instructions that, when called
within a program, results in the replacement of each such call with a code expansion consisting of the actual
instructions represented.

5-'

Chapter 5. Macros

The concepts c f macro definition, call, and expansion can be illustrated by a tYPical business form letter, where
the prototypenstructions conSISt of preset text. For example, we could define a macro CNFIRM with the text

Air FI ght welcomes you as a passenger.
Your 'Iight number FNO leaves at DTIME and arrives in DEsT at ATIME.

This macro ha, four dummy parameters to be replaced, when the macro is called, by the actual flight number,
departure time destination, and arrival time. Thus the macro call might look like

CNFII~M 123, '10:45', 'Ontario', '11 :52'

A second macro, CAR, could be called if the passenger has requested that a rental car be reserved at the desti-
nation airport. This macro might have the text

Your lutomobile reservation has been confirmed with MAKE rent-a-car agency.

Finally, a macro GREET could be defined to specify the passenger name.

Dear~AME:

The entire tex of the business letter (source file) would then look like

GREET 'Ms. scannel'
CNFl~M 123, '10:45', 'Ontario', '11:52'
CAR 'Blotz'
We tr Jst you will enioy your flight.

Since ely,

When this sou,ce file is passed through a macro processor, the macro calls are expanded to produce the following
letter.

Dear 'v1s. scannel:

Air Fight welcomes you as a passenger. Your flight number 123 leaves at 10:45 and arrives
in Ortario at 11 :52. Your automobile reservation has been confirmed with Blotz rent-a-car
agency.

We trust you will enjoy your flight.

Since'ely,

While this exallple illustrates the substitution of parameters in a macro, it overlooks the relationship of the macro
processor and the assembler. The purpose of the macro processor is to generate source code which is then
assembled.

5-2

Chapter 5. Macros

Macros Vs. Subroutines

At this point, you may be wondering how macros differ from subroutines Invoked by the CALL instruction.
Both aid program structuring and reduce the coding of frequently executed routines.

One distinction between the two IS that subroutines necessarily branch to another part of your program while
macros generate in-line code. Thus, a program contains only one version of a given subroutine, but contains as
many versions of a given macro as there are calls for that macro.

Notice the emphasis on 'versions' in the prevIous sentence, for this is a malor difference between macros and
subroutines. A macro does not necessarily generate the same source code each time it is called. By changing the
parameters In a macro call, you can change the source code the macro generates. In addition, macro parameters
can be tested at assembly-time by the conditional assembly directives. These two tools enable a general-purpose
macro definition to generate customized source code for a particular programming situation. Notice that macro
expansion and any code customization occur at assembly-time and at the source code level. By contrast, a
generalized subroutine resides in your program and requires execution time.

It IS usually possible to obtain similar results using either a macro or a subroutine. Determining which of these
facilities to use is not always an obvious decision. In some cases, uSing a single subroutine rather than multiple
In-line macros can reduce the overall program size. In situations involving a large number of parameters, the use
of macros may be more efficient. Also, notice that macros can call subroutines, and subroutines can contain
macros.

USING MACROS

The assembler recognizes the following macro operations:

.. MACRO directive
CI ENDM directive
.. LOCAL directive
CI REPT directive
.. IRP directive
.. IRPC directive
CI EXITM directive
.. Macro call

All of the directives listed above are related to macro definition. The macro call initiates the parameter sub-
stitution (macro expansion) process.

Macro Definition

Macros must be defined in your program before they can be used. A macro definition is Initiated by the MACRO
assembler directive, which lists the name by which the macro can later be called, and the dummy parameters to
be replaced during macro expansion. The macro definition is terminated by the ENDM directive. The prototype
instructions bounded by the MACRO and ENDM directives are called the macro body.

5·3

Chapter 5. Macros

When label sy mbols used in a macro body have 'global' scope, multiply-defined symbol errors result if the macro
is called more than once. A label can be given limited scope using the LOCAL directive. This directive assigns a
unique value :0 the symbol each time the macro is called and expanded. Dummy parameters also have limited
scope.

Occasionally "ou may wish to duplicate a block of code several times, either within a macro or in line with
other source ':ode. This can be accomplished with minimal coding effort using the REPT (repeat block), IRP
(indefinite repeat), and IRPC (indefinite repeat character) directives. Like the MACRO directive, these directives
are terminated by ENDM.

The EXITM c irective provides an alternate exit from a macro. When encountered, it terminates the current macro
just as if EN['M had been encountered.

Macro Definitior, Directives

MACRO Dire:tive


name MACRO optional dummy parameter(s)

The name in :he label field specifies the name of the macro body being defined. Any valid user-defined symbol
name can be Jsed as a macro name. Note that this name must be present and must not be terminated by a colon.

A dummy panmeter can be any valid user-defined symbol name or can be null. When multiple parameters are listed,
they must be ,eparated by commas. The scope of a dummy parameter is limited to its specific macro definition. If a
reserved symt 01 is used as a dummy parameter, its reserved value is not recognized. For example, if you code
A,B,C as a dLmmy parameter list, substitutions will occur properly. However, you cannot use the accumulator
or the Band::: registers within the macro. Because of the limited scope of dummy parameters, the use of these
registers is not affected outside the macro definition.

Dummy paralneters in a comment are not recognized. No substitution occurs for such parameters.

Dummy paralneters may appear in a character string. However, the dummy parameter must be adjacent to an
ampersand chlracter (&) as explained later In this chapter.

Any machine Instruction or applicable assembler directive can be included in the macro body. The distinguishing
feature of ma;ro prototype text is that parts of it can be made variable by placing substitutable dummy param-
eters in instrLction fields. These dummy parameters are the same as the symbols in the operand field of the
MACRO dire'tive.

Example:

Define macro MACl with dummy parameters Gl, G2, and G3.

5-4

Chapter 5. Macros

NOTE

The following macro definition contains a potential error
that IS clarified in the description of the LOCAL directive
later in this chapter.

MACl MACRO Gl,G2,G3 ;MACRO DIRECTIVE
MOVES: LHLD Gl ;MACRO BODY
MOV A,M
LHLD G2
MOV B,M
LHLD G3
MOV C,M
ENDM ;ENDM DIRECTIVE

ENDM Directive


ENDM

The ENDM directive is required to terminate a macro definition and follows the last prototype instruction. It is
also required to terminate code repetition blocks defined by the REPT, IRP, and IRPC directives.

Any data appearing in the label or operand fields of an ENDM directive causes an error.

NOTE

Because nested macro calls are not expanded during macro
definition, the ENDM directive to close an outer macro can-
not be contained in the expansion of an inner, 'nested'
macro call. (See 'Nested Macro Definitions' later in this
chapter.)

LOCA L Directive


LOCAL label name(s)

The specified label names are defined to have meaning only within the current macro expansion. Each time the
macro is called and expanded, the assembler assigns each local symbol a unique symbol in the form 77nnnn.

The assembler assigns ?7OOO1 to the first local symbol, 770002 to the second, and so on. The most recent symbol
name generated always indicates the total number of symbols created for all macro expansions. The assembler
never duplicates these symbols. The user should avoid coding symbols in the form ??nnnn so that there will not
be a conflict with these assembler-generated symbols.

5-5

Chapter 5. Macros

Dummy parameters included in a macro call cannot be operands of a LOCAL directive. The ~ cope of a dummy
parameter is always local to its own macro definition.

Local symbols can be defined only within a macro definition. Any number of LOCAL directves may appear in
a macro definition, but they must all follow the macro call and must precede the first line 01 prototype code.

A LOCAL directive appearing outside a macro definition causes an error. Also, a name appea-ing in the label
field of a LOCAL directive causes an error.

Example:

The definition of MACl (used as an example in the description of the MACRO directive) cOlltains a potential
error because the symbol MOVES has not been declared local. This is a potential error since no error occurs if
MACl IS called only once in the program, and the program itself does not use MOVES as a ~ymbol. However,
if MACl is called more than once, or if the program uses the symbol MOVES, MOVES is a multiply-defined
symbol. This potential error is avoided by naming MOVES in th'eoperand field of a LOCAL directive:

MACl MACRO Gl,G2,G3
LOCAL MOVES
MOVES: LHLD Gl
MOV A,M
LHLD G2
MaY B,M
LHLD G3
MaY C,M
ENDM

Assume that MACl is the only macro in the program and that it is called twice. The first tirle MACl is expanded,
MOVES IS replaced with the symbol 7?OOOl; the second time, MOVES is replaced with 7?0002. Because the
assembler encounters only these special replacement symbols, the program may contain the 'ymbol MOVES
without causing a multiple definition.

REPT Directive


optional: REPT expression

The REPT directive causes a sequence of source code lines to be repeated 'expression' times. All lines appeanng
between the REPT directive and a subsequent ENDM directive constitute the block to be repeated.

When 'expression' contains symbolic names, the assembler must encounter the definition of he symbol prior to
encountering the expression.

The insertion of repeat blocks is performed in-line when the assembler encounters the REPl directive. No
explicit call is required to cause the code insertion since the definition is an implied call for expansion.

5-6

Chapter 5. Macros

Example 1:

Rotate accumulator right six times.

ROTR6: REPT 6
RRC
ENDM

Example 2:

The following REPT directive generates the source code for a routine that fills a five-byte field with the character
stored in the accumulator:

PROGRAM CODE GENERA TED CODING

LHLD CNTR1 LHLD CNTR1
REPT 5 MOV M,A
MOV M,A INX H
INX H MOV M,A
ENDM INX H
MOV M,A
INX H
MOV M,A
INX H
MOV M,A
INX H

Example 3:

The following example illustrates the use of REPT to generate a multiplication routine. The multiplication is
accomplished through a series of shifts. If this technique is unfamiliar, refer to the example of multiplication
in Chapter 6. The example in Chapter 6 uses a program loop for the multiplication. This example replaces the
loop with seven repetitions of the four instructions enclosed by the REPT-ENDM directives.

Notice that the expansion specified by this REPT directive causes the label SKIPAD to be generated seven times.
Therefore, SKIPAD must be declared local to this macro.

FSTMUL: MVI D,D ;FAST MULTIPLY ROUTINE
LXI H,D ;MULTIPLY E*A - 16-BIT RESULT
;IN H&L
REPT 7
LOCAL SKIPAD
RLC ;;GET NEXT MULTIPLIER BIT
jNC SKIPAD ;;DON'T ADD IF BIT = D
DAD D ;;ADD MULTIPLICAND INTO ANSWER
SKIPAD: DAD H
ENDM
RLC
RNC
DAD D
RET
5-7

Chapter 5. Macros

This example ilustrates a classic programming trade-off: speed versus memory Although this example executes
more qUickly tlan the example in Chapter 6, it requires more memory.

IRP Directive


optional: IRP dummy param, <list>

The operand field for the IRP (indefinite repeat) directive must contain one macro dummy parameter followed
by a list of actual parameters enclosed In angle brackets. IRP expands its associated macro prototype code sub-
stituting the fi 'st actual parameter for each occurrence of the dummy parameter. IRP then expands the proto-
type code agai 1 substituting the second actual parameter from the list. This process continues until the list is
exhausted.

The list of actJal parameters to be substituted for the dummy parameter must be enclosed In angle brackets
« ». Individu, I items in the list must be separated by commas. The number of actual parameters in the list
controls the nilmber of times the macro body is repeated; a list of n Items causes n repetitions. An empty list
(one with no Jarameters coded) specifies a null operand list. IRP generates one copy of the macro body sub-
stituting a nul' for each occurrence of the dummy parameter. Also, two commas with no intervening character
create a null parameter within the list. (See 'Special Operators' later in this chapter for a description of null
operands.)

Example:

The following code sequence gathers bytes of data from different areas of memory and then stores them in
consecutive b~ tes beginning at the address of STORIT


LXI H,STORIT LXI H,STORIT
IRP X,<FL01,3E20H,FLD3> LOA FLOl
LOA X MOV M,A
MOV M,A INX H
INX H LDA 3E20H
ENOM MOV M,A
INX H
LOA FL03
MOV M,A
INX H

IRPC Directhe


optional: IRPC dummy param,text

5-8

Chapter 5. Macros

The IRPC (indefinite repeat character) directive causes a sequence of macro prototype instructions to be repeated
for each text character of the actual parameter specified. If the text string is enclosed in optional angle brackets,
any delimiters appearing in the text string are treated simply as text to be substituted into the prototype code.
The assembler generates one iteration of the prototype code for each character in the text string. For each
Iteration, the assembler substitutes the next character from the string for each occurrence of the dummy param-
eter. A list of n text characters generates n repetitions of the IRPC macro body. An empty string specifies a
null actual operand. IRPC generates one copy of the macro body substituting a null for each occurrence of the
dummy parameter.

Example:


LHLD DATE-l LHLD DATE-l
MVDATE: IRPC X,1977 INX H
INX H MVI M,l
MVI M,X INX H
ENDM MVI M,9
INX H
MVI M,7
INX H
MVI M,7

IRPC provides the capability to treat each character of a string individually; concatenation (described later in this
chapter) provides the capability for building text strings from Individual characters.

EXITM Directive


optional: EXITM

EXITM provides an alternate method for terminating a macro expansion or the repetition of a REPT, IRP, or
IRPC code sequence. When EX!TM is encountered, the assembler ignores all macro prototype instructions
located between the EXITM and ENDM directive for this macro. Notice that EXITM may be used in addition
to ENDM, but not in place of ENDM.

When used in nested macros, EXITM causes an exit to the previous level of macro expansion. An EXITM within
a REPT, IRP. or IRPC terminates not only the current expansion, but all subsequent iterations as well.

Any data appearing in the operand field of an EXITM directive causes an error.

Example:

EXITM is typically used to suppress unwanted macro expansion. In the following example, macro expansion is
terminated when the EX1TM directive is assembled because the condition X EQ 0 is true.

5-9

Chapter 5. Macros

MAC3 MACRO X,Y

IF X EQ 0
EXITM

ENDM

Special Macro Op?rators

In certain specal cases, the normal rules for dealing with macros do not work. Assume. for example, that you
want to specif" three actual parameters. and the second parameter happens to be the comma character. To the
assembler, the list PARM1,,,PARM3 appears to be a list of four parameters where the second and third param-
eters are missirg. The list can be passed correctly by enclosing the comma in angle brackets: PARM1,<,>,PARM3.
These special ( perators instruct the assembler to accept the enclosed character (the comma) as an actual param-
eter rather tha'l a del im iter.

The assembler recognizes a number of operators that allow special operations:

& Ampersand. Used to concatenate (link) text and dummy parameters. See the further
discussion of ampersands below.

<> Angle brackets. Used to delimit text, such as lists, that contain other delimiters.
Notice that blanks are usually treated as delimiters. Therefore, when an actual
parameter contains blanks (passing the instruction MOV A,M, for example) the
parameter must be enclosed in angle brackets. This is also true for any other de-
limiter that is to be passed as part of an actual parameter. To pass such text to
nested macro calls, use one set of angle brackets for each level of nesting. (See
'Nested Macro Definitions,' below.)

Double semicolon. Used before a comment in a macro definition to prevent
inclusion of the comment in expansions of the macro and reduce storage
requirements. The comment still appears in the listing of the definition.

Exclamation point (escape character). Placed before a character (usually a
delimiter) to be passed as literalized text in an actual parameter. Used primarily
to pass angle brackets as part of an actual parameter. To pass a literalized
exclamation point, issue!!. Carriage returns cannot be passed as actual parameters.

The 'I' is always preserved while building an actual parameter. It is not
echoed when an actual parameter is substituted for a dummy parameter,
except when the substitution is being used to build another actual parameter.

5-10

Chapter 5. Macros

NUL In certain cases it is not necessary to pass a parameter to a macro. It is
necessary, however, to indicate the omission of the parameter. The omitted
(or null) parameter can be represented by two consecutive delimiters as in
the list PARMl "PARM3. A null parameter can also be represented by two
consecutive single quotes: ",PARM2,PARM3. Notice that a null is quite
different from a blank: a blank is an ASCII character with the hexadecimal
representation 20H; a null has no character representation. In the assembly
listing a null looks the same as a blank, but that is only because no substi-
tution has taken place. The programmer must decide the meaning of a null
parameter. Although the mechanism is somewhat different, the defaults taken
for assembler controls provide a good example of what a null parameter can
mean. For example. coding MOD85 as an assembler control specifies that
the assembler is to generate obiect code for the 8085. The absence of this
control (which In effect is a null parameter) specifies that the assembler
is to generate only 8080 object code.

Assembler controls are explained in the 1515-11 8080/8085 Macro Assembler
Operator's Manual, 9800292.

Example:

In a macro with the dummy parameters W,X,Y,Z it is acceptable for either
the X or Y parameter to be null, but not both. The following IF directive
tests for the error condition:

IF NUL X&Y
EXITM

When a macro IS expanded, any ampersand preceding or following a dummy parameter in a macro definition is
removed and the substitution of the actual parameter occurs at that point. When it is not adjacent to a dummy
parameter, the ampersand is not removed and is passed as part of the macro expansion text.

NOTE

The ampersand must be immediately adjacent to the text being
concatenated; Intervening blanks are not allowed.

If nested macro definitions (described below) contain ampersands, the only ampersands removed are those adjacent
to dummy parameters belonging to the macro definition currently being expanded. All ampersands must be reo
moved by the time the expansion of the encompassing macro body is performed. Exceptions force illegal character
errors.

Ampersands placed inside strings are recognized as concatenation delimiters when adjacent to dummy parameters;
similarly, dummy parameters within character strings are recognized only when they are adjacent to ampersands.
Ampersands are not recognized as operators in comments.

5-11

Chapter 5. Macros

Nested Macro Del initions

A macro definition can be contained completely within the body of another macro definition (that is, macro
definitions can be nested). The body of a macro consists of all text (including nested macro definitions)
bounded by mltching MACRO and ENDM directives. The assembler allows any number of macro definitions to
be nested.

When a higher-evel macro is called for expansion, the next lower-level macro is defined and eligible to be called
for expansion. A lower-level macro cannot be called unless all higher-level macro definitions have already been
called and exp;.nded.

A new macro I nay be defined or an existing macro redefined by a nested macro definition depending on whether
the name of the nested macro is a new label or has previously been established as a dummy parameter in a
higher-level ma:ro definition. Therefore, each time a higher-level macro is called, a lower-level definition can be
defined differe ltly if the two contain common dummy parameters. Such redefinition can be costly, however, in
terms of assem oler execution speed.

Since IRP, IRFC, and REPT blocks constitute macro definitions, they also can be nested within another definition
created by IRF, IRPC, REPT, or MACRO directives. In addition, an element in an IRP or IRPC actual parameter
list (enclosed 1,1 angle brackets) may itself be a list of bracketed parameters; that is, lists of parameters can contain
elements that ,.re also lists.

Example:

LISTS MACRO PARAM1,PARAM2

ENDM

LISTS <A, <B,C»

MACRO CALLS

Once 'a macro las been defined, it can be called any number of times in the program. The call consists of the
macro name alid any actual parameters that are to replace dummy parameters during macro expansion_ During
assembly, each macro call is replaced by the macro definition code; dummy parameters are replaced by actual
parameters.

Macro Call Format

optional: macro name optional actual
parameter(s)

5-12

Chapter 5. Macros

The assembler must encounter the macro definition before the first call for that macro. Otherwise. the macro
call is assumed to be an illegal opcode. The assembler inserts the macro body identified by the macro name
each time it encounters a call to a previously defined macro in your program.

The positioning of actual parameters in a macro call is critical since the substitution of parameters is based
solely on position. The first-listed actual parameter replaces each occurrence of the first-listed dummy param-
eter; the second actual parameter replaces the second dummy parameter, and so on. When coding a macro call,
you must be certain to list actual parameters in the appropriate sequence for the macro.

Notice that blanks are usually treated as delimiters. Therefore, when an actual parameter contains blanks
(passing the instruction MOV A,M, for example) the parameter must be enclosed in angle brackets. This is also
true for any other delimiter that is to be passed as part of an actual parameter. Carriage returns cannot be passed
as actual parameters,

If a macro call specifies more actual parameters than are listed in the macro definition, the extra parameters
are ignored. If fewer parameters appear in the call than in the definition, a null replaces each missing parameter.

Example:

The following example shows two calls for the macro LOAD. LOAD is defined as follows:

LOAD MACRO Gl,G2,G3
LOCAL MOVES
MOVES: LHLD Gl
MOV A,M
LHLD G2
MOV B,M
LHLD G3
MOV C,M
ENDM

LOAD simply loads the accumulator with a byte of data from the location specified by the first actual parameter,
the B register with a byte from the second parameter, and the C register with a byte from the third parameter.

The first time LOAD is called, It is used as part of a routine that inverts the order of three bytes in memory.
The second time LOAD is called, it is part of a routine that adds the contents of the B register to the accumu·
lator and then compares the result with the contents of the C register.

5-13

Chapter 5. Macros

MAIN PROGRAM SUBSTITUTION

JNZ nEXT JNZ NEXT
LOA[ FLD,FLD+1,FLD+2 ??0001 . LHLD FLD
MOY M,A ;INYERT BYTES MOY A,M
DCX H LHLD FLD+1
MOY M,B MOY B.M
DCX H LHLD FLD+2
MOY M,C MOY C,M
LOM' 3EOH,BYTE,CHECK MOY M,A ;INYERT BYTES
ADD B ;CHECK DIGIT DCX H
CMP C MOY M,B
CNZ DGTBAD DCX H
MOY M,C
7?0002: LHLD 3EOH
MOY A,M
LHLD BYTE
MOY B,M
LHLD CHECK
MOY C,M
ADD B ;CHECK DIGIT
CMP C
CNZ DGTBAD

Nested Macro Calls

Macro calls (in:luding any combination of nested IRP, IRPC, and REPT constructs) can be nested within macro
definitions up to eight levels. The macro being called need not be defined when the enclosing macro is defined;
however, it ml st be defined before the enclosing macro is called.

A macro defin tlon can also contain nested calls to itself (recursIVe macro calls) up to eight levels, as long as the
recursive macr" expansions can be terminated eventually, This operation can be controlled using the conditional
assembly direc:lves described in Chapter 4 (IF, ELSE, ENDIF).

Example:

Have a macro :all itself five times after it is called from elsewhere in the program.

PARAM1 SET 5
RECALL MACRO

IF PARAM1 NE 0
PARAM1 SET PARAM1-1
RECALL ;RECURSIYE CALL
ENDIF

ENDM

5-14

Chapter 5. Macros

Macro Expansion

When a macro is called, the actual parameters to be substituted into the prototype code can be passed in one of
two modes. Normally, the substitution of actual parameters for dummy parameters is simply a text substitution.
The parameters are not evaluated until the macro is expanded.

If a percent sign (%) precedes the actual parameter in the macro call, however, the parameter is evaluated
immediately, before expansion occurs, and is passed as a decimal number representing the value of the param-
eter. In the case of IRPC, a '%' preceding the actual parameter causes the entire text string to be treated as a
single parameter. One IRPC iteration occurs for each digit in the decimal string passed as the result of immediate
evaluation of the text string.

The normal mechanism for passing actual parameters is adequate for most applications. Using the percent sign
to pre-evaluate parameters is necessary only when the value of the parameter is different within the local con-
text of the macro definition as compared to its global value outside the macro definition.

Example:

The macro shown in this example generates a number of rotate instructions. The parameters passed in the macro
call determine the number of positions the accumulator is to be rotated and whether rotate right or rotate left
instructions are to be generated. Some typical calls for this macro are as follows:

SHIFTR 'R',3
SHIFTR L,%COUNT-l

The second call shows an expression used as a parameter. This expression is to be evaluated immediately rather
than passed simply as text.

The definition of the SHIFTR macro is shown below. This macro uses the conditional IF directive to test the
validity of the first parameter. Also, the REPT macro directive is nested within the SHIFTR macro.

SHIFTR MACRO X,Y
IF X EQ 'R'
REPT Y
RAR
ENDM
ENDIF
IFXNE'L'
EXITM
ELSE
REPT Y
RAL
ENDM
ENDIF
ENDM

The indentation shown in the definition of the SHIFTR macro graphically illustrates the relationships of the IF,
ELSE, ENDIF directives and the REPT. ENDM directives. Such indentation is not required in your program, but
may be desirable as documentation.

5-15

Chapter 5. Macros

The SHI FTRllacro generates nothing if the first parameter is neither R nor L. Therefore, the following calls
produce no c(,de. The result in the object program is as though the SHIFTR macro does not appear in the
source program.

SHIFTR 5
SHIFTR 'B',2

The following call to the SHIFTR macro generates three RAR instructions:

SHIFTR 'R',3

Assume that, SET directive elsewhere in the source program has given COUNT the value 6. The following call
generates five RAL instructions:

SHIFTR 'L ',%COUNT -1

The following is a redefinition of the SHIFTR macro. In this definition, notice that concatenation is used to
form the RAf: or RAL operation code. If a call to the SHIFTR macro specifies a character other than R or L,
illegal operati,m codes are generated. The assembler flags all illegal operation codes as errors.

SHIFTR MACRO X,y
REPT Y
RA&X
ENDM
ENDM

NULL MACROS

A macro may legally comprise only the MACRO and ENDM directives. Thus, the following is a legal macro
definition:

NADA MACRO P1,P2,P3,P4
ENDM

A call to thiS macro produces no source code and therefore has no effect on the program.

Although thel e is no reason to write such a macro, the null (or empty) macro body has a practical application.
For example, all the macro prototype instructions might be enclosed With IF-ENDIF conditional directives.
When none 0', the specified conditions IS satisfied. all that remainS of the macro is the MACRO directive and
the ENDM di ·ective.

SAMPLE MACR05

The followin! sample macros further demonstrate the use of macro directives and operators.

5-16

Chapter 5. Macros

Example 1: Nested IRPC

The following macro definition contains a nested IRPC directive. Notice that the third operand of the outer
macro becomes the character string for the IRPC:

MOVE MACRO X,Y,l
IRPC PARAM,l
LHLD X&&PARAM
SHLD Y&&PARAM
ENDM
ENDM

Assume that the program contains the call MOVE SRC,DST,123. The third parameter of this call IS passed to
the IRPC. This has the same effect as coding IRPC PARAM,123. When expanded, the MOVE macro generates
the following source code:

LHLD SRCl
SHLD DSTl
LHLD SRC2
SHLD DST2
LHLD SRC3
SHLD DSn

Notice the use of concatenation to form labels in this example.

Example 2: Nested Macros Used to Generate DB Directives

This example generates a number of DB 0 directives, each With ItS own label. Two macros are used for this
purpose: INC and BLOCK. The INC macro is defined as follows:

INC MACRO Fl,F2
$ SAVE GEN
Fl&F2: DB 0 ;GENERATE LABELS & DB's
RESTORE
ENDM

The BLOCK macro, which accepts the number of DB's to be generated (NUMB) and a label prefix (PREFIX), is
defi ned as follows:

BLOCK MACRO NUMB,PREFIX
$ SAVE NOGEN
COUNT SET o
REPT NUMB
COUNT SET COUNT+l
INC PREFIX,%COUNT ;NESTED MACRO CALL
ENDM
$ RESTORE
ENDM

5-17

Chapter 5. Macros

The macro ca I BLOCK 3.LAB generates the following source code:

BLOCK 3.LAB
LABl: DB o
LAB2: DB o
LAB3: DB o

The assemblet controls specified in these two macros (the lines beginning with $) are used to clean up the
assembly Iistit,g for easier reading. The source code shown for the call BLOCK 3.LAB is what appears in the
assembly listillg when the controls are used. Without the controls. the assembly listing appears as follows:

BLOCK 3.LAB
COUNT SET 0
REPT 3
COUNT SET COUNT+l
INC LAB.%COUNT
ENDM
COUNT SET COUNT+1
INC LAB.%COUNT
LAB1: DB 0
COUNT SET COUNT+l
INC LAB.%COUNT
LAB2: DB 0
COUNT SET COUNT+l
INC LAB.%COUNT
LAB3: DB 0

Example 3: " Macro that Converts Itself into a Subroutine

In some case5. the in-line coding substituted for each macro call imposes an unacceptable memory requirement.
The next thrEe examples show three different methods for converting a macro call into a subroutine call. The
first time the SBMAC macro is called. it generates a full in-line substitution which defines the SUBR subroutine.
Each subsequ;nt call to the SBMAC macro generates only a CALL instruction to the SUBR subroutine.

Within the fo.lowing examples. notice that the label SUBR must be global so that it can be called from outside
the first expa 1sion. This IS possible only when that part of the macro definition containing the global label is
called only Ollce in the entire program.

Method #1: i~ested Macro Definitions

Macros can b" redefined during the course of a program. In the following example. the definition of SBMAC
contains its own redefinition as a nested macro. The first time SBMAC is called, it is full expanded. and the
redefinition of SBMAC replaces the original definition. The second time SBMAC IS called. only its redefinition
(a CALL inst"uction) is expanded.

5-18

Chapter 5. Macros

SBMAC MACRO
SBMAC MACRO
CALL SUBR ;;REDEFINITION OF SBMAC
ENDM
CALL SUBR
LINK: jMP DUN
SUBR:

RET
DUN:
ENDM

Notice that both versions of SBMAC contain CALL SUBR instructions. This is necessary to provide a return
address at the end of the SUBR routine. The jump instruction labelled LINK is required to prevent the SUBR
subroutine from executing a return to itself. Notice that the return address for the second CALL SUBR
instruction would be SUBR if the jump instruction were omitted. The j MP DUN instruction simply transfers
control past the end of the subroutine.

NOTE

The assembler allows the use of a source line consisting
only of a label. Such a label IS assigned to the next source
line for which code or data is generated. Notice that
neither code nor data is generated for an ENDM directive,
so the label DUN is assigned to whatever instruction follows
the ENDM directive. This construct is required because the
ENDM directive itself may not be given a label.

Method #2: Conditional Assembly

The second method for altering the expansion of the SBMAC macro uses conditional assembly. In this example,
a switch (FI RST) is set TRUE just before the first call for SBMAC. SBMAC is defined as follows:

TRUE EQU OFFH
FALSE EQU 0
FIRST SET TRUE
SBMAC MACRO
CALL SUBR
IF FIRST
FIRST SET FALSE
LINK: jMP DUN
SUBR:

RET
DUN:
ENDIF
ENDM

5-19

Chapter 5. Macros

The first call 0 SBMAC expands the full definition, including the call to and definition of SUBR:

SBMAC
CALL SUBR
IF FIRST
LINK: JMP DUN
SUBR:

RET
DUN:
ENDIF

Because FI RS r is TRUE when encountered during the first expansion of SBMAC, all the statements between
IF and ENDI!' are assembled into the program. In subsequent calls, the conditionally-assembled code is skipped
so that the sUJroutine is not regenerated. Only the following expansion is produced:

SBMAC
CALL SUBR
IF FIRST

Method #3: :onditlonal Assembly with EXITM

The third met hod for altering the expansion of SBMAC also uses conditional assembly. but uses the EXIT M
directive to Sl ppress unwanted macro expansion after the first call. EXITM is effective when FIRST is FALSE,
which it is aft er the first call to SBMAC.

TRUE EQU OFFH
FALSE EQU 0
FIRST SET TRUE
SBMAC MACRO
CALL SUBR
IF NOT FIRST
EXITM
ENDIF
FIRST SET FALSE
JMP DUN
SUBR:

RET
DUN:
ENDM

5-20

Chapter 5. Macros

Example 4: Computed GOTO Macro

This sample macro presents an implementation of a computed GOTO for the 8080 or 8085. The computed
GOTO, a common feature of many high level languages, allows the program to jump to one of a number of
different locations depending on the value of a variable. For example, if the variable has the value zero, the
program jumps to the first item In the list; if the variable has the value 3, the program jumps to the fourth
address In the list.

In this example, the variable IS placed in the accumulator. The list of addresses is defined as a series of DW
directives starting at the symbolic address TABLE. This macro (T JUMP) also modifies itself with a nested
definition. Therefore, only the first call to the TJ UMP macro generates the calculated GOTO routine. Subse-
quent calls produce only the jump instruction JMP TJCODE.

TJUMP MACRO ;JUMP TO A-TH ADDR IN TABLE
TJCODE: ADD A ;MULTIPLY A BY 2
MVI D,O ;CLEAR DREG
MOV E,A ;GET TABLE OFFSET INTO D&E
DAD D ;ADD OFFSET TO TABLE ADDR IN H&L
MOV E,M ;GET 1ST ADDRESS BYTE
INX H
MOV D,M ;GET 2ND ADDRESS BYTE
XCHG
PCHL ;J UMP TO ADDRESS
TJUMP MACRO ;REDEFINE TJUMP TO SAVE CODE
JMP TJCODE ;NEXT CALL JUMPS TO ABOVE CODE
ENDM
ENDM

Notice that the definition of the TJ UMP macro does not account for loading the address of the address table
into the Hand L registers; the user must load this address just before calling the TJ UMP macro. The following
shows the coding for the address table (TABLE) and a typical call sequence for the TJ UMP macro:

MVI A,2
LXI H,TABLE
TJUMP

TABLE: DW LOCO
DW LOC1
DW LOC2

The call sequence shown above causes a lump to LOC2.

5-21

Chapter 5. Macros

Example 5: Using IRP to Define the Jump Table

The TJ UMP macro becomes even more useful when a second macro (GOTOl IS used to define the jump table,
load the addr"ss of the table Into the Hand L registers, and then call TJ UMP, The GOTO macro is defined as
follows:

GOTO MACRO INDEX,L1ST
LOCAL JTABLE
LDA INDEX ;LOAD ACCUM WITH INDEX
LXI H,JTABLE ;LOAD H&L WITH TABLE ADDRESS
TJUMP ;CALL TJUMP MACRO
)TABLE: IRP FORMAL,(L1ST>
DW FORMAL ;SET UP TABLE
ENDM
ENDM

A typical call to the GOTO macro would be as follows:

GOTO CASE,(COUNT,TIMER,DATE,PTDRVR>

This call to He GOTO macro builds a table of DW directives for the labels COUNT, TIMER, DATE, and
PTDRVR. It hen loads the base address of the table into the Hand L registers and calls the Tj UMP macro.
If the value o' the variable CASE is 2 when the GOTO macro is called, the GOTO and TJ UMP macros
together causl a jump to the address of the DATE routine.

Notice that allY number of addresses may be specified in the list for the GOTO routine as long as they all fit
on a single so Jrce line. Also, the GOTO macro may be called any number of times, but only one copy of the
coding for thl TjUMP is generated since the TJUMP macro redefines itself to generate only a jMP TjCODE
instruction.

5-22

6. PROGRAMMING TECHNIQUES

This chapter describes some techniques that may be of help to the programmer.

BRANCH TABLES PSEUDO-SUBROUTINE

Suppose a program consists of several separate routines. any of which may be executed depending upon some
initial condition (such as a number passed In a register). One way to code this would be to check each condition
sequentially and branch to the routines accordingly as follows:

CONDITION = CONDITION ]I
IF YES BRANCH TO ROUTINE 1
CONDITION = CONDITION 2?
IF YES BRANCH TO ROUTINE 2

BRANCH TO ROUTINE N

A sequence as above is inefficient. and can be improved by using a branch table.

The logic at the beginning of the branch table program loads the starting address of the branch table into the H
and L registers. The branch table itself consists of a list of starting addresses for the routines to be branched to.
Using the Hand L registers as a pointer. the branch table program loads the selected routine's starting address
into the program counter. thus effecting a jump to the desired routine. For example. consider a program that
executes one of eight routines depending on which bit of the accumulator is set:

Jump to routine 1 if the accumulator holds 00000001
2 .. .. 00000010
3 .... .. 00000100
4" If .. 00001000
5 II lJ
.. 00010000
6 II " .. 00100000
7" " .. 01000000
8 II II .. 10000000

A program that provides such logic follows. The program is termed a 'pseudo-subroutine' because it IS treated as a
subroutine by the programmer (i.e .• it appears just once in memory), but is entered via a regular JUMP instruction
rather than via a CALL Instruction.

6-1

Chapter 6. Programming Techniques

Main Pre gram Branch Table Jump
Program Routines

I

normal subroutine return
sequence not followed by
branch table program

6-2


Label Code Operand

START: LXI H.BTBL ;REGISTERS HAND L WILL
;POINT TO BRANCH TABLE
GTBIT: RAR
jC GETAD
INX H ;(H.L)=(H,L)+2 TO
INX H ;POINT TO NEXT ADDRESS
;IN BRANCH TABLE
JMP GTBIT
GETAD: MOV E,M ;BIT FOUND
INX H ;LOAD JUMP ADDRESS
;INTO D AND E REGISTERS
MOV D.M
XCHG ;EXCHANGE D AND E
;WITH HAND L
PCHL ;JUMP TO ROUTINE
;ADDRESS

BTBL: DW ROUTl ;BRANCH TABLE. EACH
DW ROUT2 :ENTRY IS A TWO-BYTE
DW ROUTJ ;ADDRESS
DW ROUT4 ;HELD LEAST SIGNIFICANT
DW ROUTS ;BYTE FIRST
DW ROUT6
DW ROUT7
DW ROUT8

The control routine at START uses the Hand L registers as a pointer into the branch table (BTBL) corresponding
to the bit of the accumulator that is set. The rdutine at GETAD then transfers the address held In the corres-
ponding branch table entry to the Hand L registers via the D and E registers. and then uses a PCH L Instruction.
thus transferring control to the selected routine.

TRANSFERRING DATA TO SUBROUTINES

A subroutine typically requires data to perform its operations. In the simplest case. this data may be transferred
In one or more registers.

Sometimes it is more convenient and economical to let the subroutine load its own registers. One way to do this
is to place a list of the required data (called a parameter list) in some data area of memory. and pass the address
of this list to the subroutine in the Hand L registers.

6-3


For example, the subroutine ADSUB expects the address of a three-byte parameter list in the Hand L registers.
It adds the fiJ st and second bytes of the list, and stores the result in the third byte of the list:

Label Code Operand Comment

LXI H.PLlST ;LOAD HAND L WITH
;ADDRESSES OF THE PARAM-
;ETER LIST
CALL ADSUB ;CALL THE SUBROUTINE
RET1:

'LIST DB 6 ;FIRST,NUMBER TO BE ADDED
DB 8 ;SECOND NUMBER TO BE
;ADDED
DS 1 ;RESULT WILL BE STORED HERE
LXI H.L1ST2 ;LOAD HAND L REGISTERS
CALL ADSUB ;FOR ANOTHER CALL TO ADSUB
RET2:

L1ST2: DB 10
DB 35
DS 1

PDSUB: MOV A,M ;GET FIRST PARAMETER
INX H ;INCREMENT MEMORY
;ADDRESS
MOV B.M ;GET SECOND PARAMETER
ADD B ;ADD FIRST TO SECOND
INX H ;INCREMENT MEMORY
;ADDRESS
MOV M,A ;STORE RESU LTAT TH IRD
;PARAMETER STORE
RET ;RETURN UNCONDITIONALLY

The first time ADSUB is called, it loads the A and B registers from PLiST and PLlST+1 respectively, adds them,
and stores tr e result in PLiST+2. Return is then made to the instruction at RET1.

6-4


First call to ADSUB:

06 PLIST

08 PLlST+l

OEH PLlST+2

The second time ADSUB IS called, the Hand L registers POint to the parameter list L1ST2. The A and B
registers are loaded with 10 and 35 respectively, and the sum is stored at L1ST2+2. Return is then made to
the Instruction at RET2.

Note that the parameter lists PLIST and L1ST2 could appear anywhere in memory without altering the results
produced by ADSUB.

This approach does have its limitations, however. As coded, ADSUB must receive a list of two and only two
numbers to be added, and they must be contiguous in memory. Suppose we wanted a subroutine (GENAD)
which would add an arbitrary number of bytes, located anywhere in memory. and leave the sum in the accumu-
lator.

This can be done by passing the subroutine a parameter list which is a list of addresses of parameters, rather
than the parameters themselves. and signifying the end of the parameter list be a number whose first byte is
FFH (assuming that no parameters will be stored above address FFOOH).

Call to GENAD:

H L

D
GENAD:

PARMl

ADRl PARM4
ADR2
ADR3 PARM3
ADR4
FFFF PARM2

As implemented below, GENAD saves the current sum (beginning with zero) in the C register. It then loads the
address of the first parameter into the D and E registers. If this address is greater than or equal to FFOOH, it
reloads the accumulator with the sum held in the C register and returns to the calling routine. Otherwise, it

6-5


loads the panmeter into the accumulator and adds the sum in the C register to the accumulator. The routine
then loops b:,ck to pick up the remaining parameters.


LXI H,PLlST ;LOAD ADDRESS OF
CALL GENAD ;PARAMETER ADDRESS LIST

HALT
PLlST: DW PARM1 ;L1ST OF PARAMETER ADDRESSES
DW PARM2
DW PARM3
DW PARM4
DW OFFFFH ;TERMINATOR

PA.RM1 : DB 6
PARM4: DB 16

FARM3: DB 13

FARM2: DB 82

GENAD: XRA A ;CLEAR ACCUMULATOR
LOOP: MOV C,A ;SAVE CURRENT TOTAL IN C
MOV E,M ;GET LOW ORDER ADDRESS BYTE
;OF FIRST PARAMETER
INX H
MOV A,M ;GET HIGH ORDER ADDRESS BYTE
;OF FIRST PARAMETER
CPI OFFH ;COMPARE TO FFH
jZ BACK ;IF EQUAL, ROUTINE IS COMPLETE
MOV D,A ;D AND E NOW ADDRESS PARAMETER
LDAX D ;LOAD ACCUMULATOR WITH PARAMETER
ADD C ;ADD PREVIOUS TOTAL
INX H ;INCREMENT HAND L TO POINT
;TO NEXT PARAMETER ADDRESS
JMP LOOP ;GET NEXT PARAMETER
BACK: MOV A,C ;ROUTINE DONE - RESTORE TOTAL
RET ;RETURN TO CALLING ROUTINE
END

6-6

Chapter 6. Programmmg Techniques

Note that GENAD could add any combination of the parameters with no change to the parameters themselves.

The sequence:
LXI H,PLlST
CALL GENAD

PUST: DW PARM4
DW PARMl
DW OFFFFH

would cause PARMl and PARM4 to be added, no matter where in memory they might be located (excluding
addresses above FFOOH).

Many variations of parameter passing are possible. For example, if it IS necessary to allow parameters to be
stored at any address, a calling program can pass the total number of parameters as the first parameter; the
subroutine then loads this first parameter into a register and uses It as a counter to determine when all param-
eters had been accepted.

SOFTWARE MULTIPLY AND DIVIDE

The multiplication of two unsigned 8-bit data bytes may be accomplished by one of two techniques: repetitive
addition, or use of a register shifting operation.

Repetitive addition provides the simplest, but slowest, form of multiplication. For example, 2AH*74H may be
generated by adding 74H to the (initially zeroed) accumulator 2AH times.

Shift operations provide faster multiplication. Shifting a byte left one bit is equivalent to multiplying by 2, and
shifting a byte right one bit IS equivalent to dividing by 2. The following process will produce the correct 2-byte
result of multiplying a one byte multiplicand by a one byte multiplier:

A. Test the least significant bit of multiplier. If zero, go to step b. If one, add the
multiplicand to the most significant byte of the result.

B. Shift the entire two-byte result right one bit position.

C. Repeat steps a and b until all 8 bits of the multiplier have been tested.

For example, consider the multiplication: 2AH*3CH=9D8H

Step 1: Test multiplier O-bit; it is 0, so shift 16-bit result right one bit.

Step 2: Test multiplier l-bit; it is 0, so shift 16-bit result right one bit.

Step 3: Test multiplier 2-blt; it is 1, so add 2AH to high-order byte of result and shift 16-bit
result right one bit.

6-7


Step 4: Test multiplier 3-bit; it is 1, so add 2AH to high-order byte of result and shift 16-bit



Step 7: Test multiplier 6-bit; it is 0, so shift 16-bit result right one bit.

Step 8: Test multiplier 7-bit; it is 0, so shift 16-bit result right one bit.

The result produced is 09D8.

HIGH-ORDER BYTE LOW-0RDER BYTE
MULTIPLIER MULTIPLICAND OF RESULT OF RESULT
Start 00111100(3C) 00101010(2A) 00000000 00000000
Step 1 a
b 00000000 00000000
Step 2 a
b 00000000 00000000
Step 3 a . '>.,., ..•. , , 00101010 00000000
b 00010101 00000000
Step 4 a . . . . , ... 00111111 00000000
b 00011111 10000000
Step 5 a ".,." . " . ' .. "" , 01001001 10000000
b 00100100 11000000
Step 6 a .. """" .. 01001110 11000000
b 00100111 01100000
Step 7 a . '" 0 .• ' · · · •• ,

b 00010011 10110000
Step 8 a . ..0 . . .
b 00001001 11 011 000(9D8)

Since the mliitiplication routine described above uses a number of important programming techniques, a sample
program IS g ven with comments.

The prograrr uses the B register to hold the most significant byte of the result. and the C register to hold the
least signific,Lnt byte of the result. The 16-bit right shift of the result is performed in the accumulator by two
rotate-right-! hrough -carry instructions.

6-8


Zero carry and then rotate B:

B C

I ~~0
[_ _ _I D
Then rotate C to complete the shift:
B C

D 'I~b
Register D holds the multiplicand. and register C originally holds the multiplier.

MULT: MVI B.O ;INITIALIZE MOST SIGNIFICANT BYTE
;OF RESULT
MVI E,9 ;BIT COUNTER
MULTO: MOV A,C ;ROTATE LEAST SIGNIFICANT BIT OF
RAR ;MULTIPLIER TO CARRY AND SHIFT
MOV C,A ;LOW-ORDER BYTE OF RESULT
DCR E
JZ DONE ;EXIT IF COMPLETE
MOV A.B
JNC MULT1
ADD D ;ADD MULTIPLICAND TO HIGH-
;ORDER BYTE OF RESULT IF BIT
;WAS A ONE
MULT1: RAR ;CARRY=O HERE SHIFT HIGH-
;ORDER BYTE OF RESULT
MOV BA
JMP MULTO
DONE:

An analogous procedure is used to divide an unsigned 16-bit number by an unsigned 16-bit number. Here, the
process involves subtraction rather than addition, and rotate-left instructions instead of rotate-right instructions.

6-9


The followin: reentrant program uses the Band C registers to hold the dividend and quotient, and the D and E
register to held the divisor and remainder. The Hand L registers are used to store data temporarily.

DIV: MOV A,D :NEGATE THE DIVISOR
CMA
MOV D,A
MOV A,E
CMA
MOV E,A
INX D :FOR TWO'S COMPLEMENT
LXI H,O ;IN ITIAL VALUE FOR REMAINDER
MVI A,17 ;INITIALIZE LOOP COUNTER
DVO: PUSH H ;SAVE REMAINDER
DAD D ;SUBTRACT DIVISOR (ADD NEGATIVE)
JNC DVl :UNDER FLOW, RESTORE HL
XTHL
DV1: POP H
PUSH PSW :SAVE LOOP COUNTER (A)
MOV A,C ;4 REGISTER LEFT SHIFT
RAL ;WITH CARRY
MOV C,A ;CY->C->B->L->H
MOV A,B
RAL
MOV BA
MOV A,L
RAL
MOV L,A
MOV A,H
RAL
MOV H,A
POP PSW :RESTORE LOOP COUNTER (A)
DCR A ;DECREMENT IT
JNZ DVO :KEEP LOOPING

;POST·DIVIDE CLEAN UP
:SHIFT REMAINDER RIGHT AND RETURN IN DE

ORA A
MOV A.H
RAR
MOV D,A
MOV A,L
RAR
MOV E,A
RET
END

6·10


MULTI BYTE ADDITION AND SUBTRACTION

The carry flag and the ADC (add with carry) instructions may be used to add unsigned data quantities of
arbitrary length. Consider the following addition of two three-byte unsigned hexadecimal numbers:

32AF8A
+84BA90
B76A1A

To perform this addition, add to the low-order byte uSing an ADD instruction. ADD sets the carry flag for use
in subsequent instructions, but does not Include the carry flag in the addition. Then use ADC to add to all
higher order bytes.

3n
~
8A
84 BA 90

B7 I 6A
i
1A

carry = 1 ...J carry = 1 . J

The following routine will perform this multibyte addition, making these assumptions:

The E register holds the length of each number to be added (in this case, 3).

The numbers to be added are stored from low-order byte to high-order byte beginning at memory locations
FI RST and SECND, respectively.

The result will be stored from low-order byte to high-order byte beginning at memory location FIRST, replacing
the original contents of these locations.

MEMORY
LOCATION before after

FIRST 8A --+ ,. lA ~ carry

FIRST+l

FIRSTt2
AF

32
--t +--
+-liI>-
6A

B7
~ carry

SECND 90 90

SECND+l BA BA

SECND+2 84 84

6-11


The followin: routine uses an ADC instruction to add the low-order bytes of the operands. This could cause
the result to be high by one if the carry flag were left set by some previous instruction. This routine avoids
the problem Jy clearing the carry flag with the XRA instruction just before LOOP.


I~ADD: LXI B,FIRST ;B AND C ADDRESS FIRST
LXI H,SECND ;H AND L ADDRESS SECND
XRA A ;CLEAR CARRY FLAG
LOOP: LDAX B ;LOAD BYTE OF FIRST
ADC M ;ADD BYTE OF SECND
;WITH CARRY
STAX B ;STORE RESULT AT FIRST
DCR E ;DONE IF E = 0
JZ DONE
INX B ;POINT TO NEXT BYTE OF
;FIRST
INX H ;POINT TO NEXT BYTE OF
;SECND
JMP LOOP ;ADD NEXT TWO BYTES
DONE:

FIRST DB 90H
DB OBAH
DB 84H
~ECND: DB 8AH
DB OAFH
DB 32H

Since none cf the instructions in the program loop affect the carry flag except ADC, the addition with carry will
proceed cornctly.

When locaticn DONE is reached. bytes FIRST through FIRST+2 will contain 1A6AB7, which is the sum shown
at the beginldng of this section arranged from low-order to high-order byte.

In order to (reate a multibyte subtraction routine, it is necessary only to duplicate the multibyte addition routine
of this sectic n, changing the ADC instruction to an SBB instruction. The program will then subtract the number
beginning at SECND from the number beginning at FIRST, placing the result at FIRST.

DECIMAL ADDIlION

Any 4-bit d, ta quantity may be treated as a decimal number as long as it represents one of the decimal digits
from 0 throllgh 9, and does not contain any of the bit patterns representing the hexadecimal digits A through F.
In order to preserve this decimal interpretation when performing addition, the value 6 must be added to the
4-bit quantily whenever the addition produces a result between 10 and 15. This is because each 4-bit data
quantity car hold 6 more combinations of bits than there are decimal digits.

6-12


Decimal addition is performed by letting each 8-bit byte represent two 4-bit decimal digits. The bytes are
summed In the accumulator in standard fashion, and the DAA (decimal adiust accumulator) instruction is then
used to convert the 8-bit binary result to the correct representation of 2 decimal digits. For multibyte strings,
you must perform the decimal adiust before adding the next higher-order bytes. This is because you need the
carry flag setting from the DAA instruction for adding the higher-order bytes.

To perform the decimal addition:

2985
+4936
7921

the process works as follows:

1. Clear the Carry and add the two lowest-order digits of each number (remember that each 2
decimal digits are represented by one byte).

85 = 10000101 B
36 = 00110110B
carry 0
Q]10111011B

Carry = 0 ~ ~ Auxiliary Carry = 0

The accumulator now contains OBBH.

2. Perform a DAA operation. Since the rightmost four bits are greater than 9, a 6 is added to the
accumulator.

Accumulator = 10111011 B
6 = 0110B
11000001 B

Since the leftmost bits are greater than 9. a 6 is added to these bits, thus setting the carry flag_

6=0110 B

/]00100001B

Carry flag = 1

The accumulator now contains 21 H. Store these two digits.

6-13


3, Add the next group of two digits:

29 = 001 01 001 B
49 = 01001001B

carry

.Q] 0111 0011 B
Carry = 0 ~ ~AuXiliary Carry = 1

The accumulator now contains 73H.

Perform a DAA operation. Since the auxiliary carry flag is set. 6 is added to the accumulator.

6 = 0110B

/QlOl111001B

Carry flag = 0

Since the leftmost 4 bits are less than 10 and the carry flag is reset, no further action occurs.

Thus, the correct decimal result 7921 IS generated in two bytes.

A routine wlich adds decimal numbers, then, IS exactly analogous to the multibyte addition routine MADD of
the last sect on, and may be produced by Inserting the instruction DAA after the ADC M instruction of that
example.

Each iteration of the program loop will add two decimal digits (one byte) of the numbers.

DECIMAL SUBTltACTION

DeCimal subtraction is considerably more complicated than decimal addition. In general, the process consists of
generating tle tens complement of the subtrahend digit, and then adding the result to the minuend digit. For
example, to subtract 34 from 56, form the tens complement of 34 (99-34=65+1=66), Then, 56+66=122. By
truncating eff the carry out of the high order digit, we get 22, the correct result.

The problerl of handling borrows arises in multibyte deCimal subtractions. When no borrow occurs from a sub-
tract, you v'ant to use the tens complement of the subtrahend for the next operation. If a borrow does occur,
you want t,. use the nines complement of the subtrahend.

Notice that the meaning of the carry flag IS Inverted because you are dealing with complemented data. Thus, a
one bit in tle carry flag Indicates no borrow: a zero bit In the carry flag indicates a borrow. This inverted carry
flag setting :an be used in an add operation to form either the nines or tens complement of the subtrahend.

6-14


The detailed procedure for subtracting multi-digit decimal numbers is as follows:

1. Set the carry flag = 1 to indicate no borrow.

2. Load the accumulator with 99H, representing the number 99 decimal.

3. Add zero to the accumulator with carry, producing either 99H or 9AH, and resetting the
carry flag.

4. Subtract the subtrahend digits from the accumulator. producing either the nines or tens
complement.

5. Add the minuend digits to the accumulator.

6. Use the DAA instruction to make sure the result In the accumulator is In decimal format, and
to indicate a borrow in the carry flag if one occurred.

7. If there are more digits to subtract, go to step 2. Otherwise. stop.

Example:

Perform the decimal subtraction:

43580
-13620

29960

1. Set carry = 1 .

2. Load accumulator with 99H.

3. Add zero with carry to the accumulator, producing 9AH.

= 000000008
Carry

100110108 = 9AH
4. Subtract the subtrahend digits 62 from the accumulator.

62 = 1001111 08
] 001110008

6-15

Chapter 6. Programming -rechniques

5. Add the minuend digits 58 to the accumulator.

Accumulator = 00111 OOOB
58 = 01011 OOOB

Q] 1001 OOOOB = 90H
Carry = 0 ~ 'AUXiliarY Carry = 1

6. DAA converts accumulator to 96 (since Auxiliary Carry = 1) and leaves carry flag =0
Indicating that a borrow occurred.

7 Load accumulator with 99H.

8. Add zero with carry to accumulator. leaving accumulator = 99H.

9. Subtract the subtrahend digits 13 from the accumulator.

Accumulator = 10011 001 B
13= 11101101B
1] 10000110B

10. Add the minuend digits 43 to the accumulator.

Accumulator = 1000011 OB
43 = 01000011 B

~~ 11001001B = C9H

Carry = 0 'AUXiliary Carry = 0

11 DAA converts accumulator to 29 and sets the carry flag = 1. indicating no borrow occurred.

Therefore, the result of subtracting 1362 from 4358 is 2996.

The followinl. subroutine will subtract one 16-digit decimal number from another using the following assumptions:

The minuend IS stored least significant (2) digits first beginning at location MINU.

The subtrahe ld IS stored least significant (2) digits first beginning at location SBTRA.

The result will be stored least significant (2) digits first, replacing the minuend.

6-16



DSUB: LXI D,MINU ;D AND E ADDRESS MINUEND
LXI H,SBTRA ;H AND L ADDRESS SUBTRA-
;HEND
MVI C,8 ;EACH LOOP SUBTRACTS 2
;DIGITS (ONE BYTE),
;THEREFORE PROGRAM WILL
;SUBTRACT 16 DIGITS.
STC ;SET CARRY INDICATING
;NO BORROW
LOOP: MVI A,99H ;LOAD ACCUMULATOR
;WITH 99H.
ACI 0 ;ADD ZERO WITH CARRY
SUB M ;PRODUCE COMPLEMENT
;OF SUBTRAHEND
XCHG ;SWITCH D AND E WITH
;H AND L
ADD M ;ADD MINUEND
DAA ;DECIMAL ADJUST
;ACCUMULATOR
MOV M,A ;STORE RESULT
XCHG ;RESWITCH D AND E
;WITH HAND L
DCR C ;DONE IF C = 0
JZ DONE
INX D ;ADDRESS NEXT BYTE
;OF MINUEND
INX H ;ADDRESS NEXT BYTE
;OF SUBTRAHEND
JMP LOOP ;GET NEXT 2 DECIMAL DIGiTS
DONE: NOP

6-17

7. INTERRUPTS

INTERRUPT CONCEPTS

The following is a general description of interrupt handling and applies to both the 8080 and 8085 processors.
However, the 8085 processor has some additional hardware features for interrupt handling. For more infor-
mation on these features, see the description of the 8085 processor in Chapter 1 and the descriptions of the
RIM, SIM, and RST instructions in Chapter 3.

Often, events occur external to the central processing unit which require immediate action by the CPU. For
example, suppose a device is sending a string of 80 characters to the CPU, one at a time, at fixed intervals.
There are two ways to handle such a situation:

A. A program could be written which accepts the first character, waits until the next character is
ready (e.g., executes a timeout by incrementing a sufficiently large counter), then accepts the
next character, and proceeds in this fashion until the entire 80 character string has been received.

This method is referred to as programmed Input/Output.

B. The device controller could interrupt the CPU when a character is ready to be input, forcing a
branch from the executing program to a special interrupt service routine.

The interrupt sequence may be illustrated as follows:

INTERRUPT

Normal Program
Program Execution
Execution Continues

Interrupt Service
Routine

7-1

Chapter 7. Interrupts

The 8080 cor tains a bit named INTE which may be set or reset by the instructions EI and DI described in
Chapter 3. Wilenever INTE is equal to 0, the entire interrupt handling system is disabled, and no interrupts
will be accepl ed.

When the 8010 recognizes an interrupt request from an external device, the following actions occur:

1. The instruction currently being executed is completed.

2. The interrupt enable bit. INTE, is reset = O.

3. The interrupting device supplies. via hardware. one instruction which the CPU executes. This
instruction does not appear anywhere in memory, and the programmer has no control over it,
since it is a function of the interrupting device's controller design. The program counter is not
incremented before this instruction.

The Instruction supplied by the interrupting device is normally an RST instruction (see Chapter 3), since this
is an efficienl one byte call to one of 8 eight-byte subroutines located in the first 64 words of memory. For
instance, the jevice may supply the instruction:

RST OH

with each in, ut interrupt. Then the subroutine which processes data transmitted from the deVice to the CPU
will be called into execution via an eight-byte instruction sequence at memory locations OOOOH to 0007H.

A digital inplt device may supply the instruction:

RST 1H

Then the sub'outine that processes the digital input signals will be called via a sequence of instructions
occupying m"mory locations 0008H to OOOFH.

d
Transfers

:epvpi~i::a~ST OH .~ 0000
Beginning of
c_o_n_t_ro_l_t_o subroutine for
0007 } device 'a'

Device "
d T_ra_n_s_fe_r_s
control to .-
• 0008
I Beginning of
subroutine for
supplie, RST 1 H OOOF
J device 'b'

7-2


Transfers

}
Beginning of
Device 'x' control to 0038
subroutine for
supplies RST 7H 003F
device 'x'

Note that any of these 8-byte subroutines may in turn call longer subroutines to process the interrupt, if
necessary.

Any device may supply an RST instruction (and indeed may supply anyone-byte 8080 instruction).

The following is an example of an Interrupt sequence:

ARBITRARY
MEMOR Y ADDRESS INSTRUCTION

~3COC
3COB
~~~ ~'1~{,o",,"p<f,om D,,'ce , A

I
Device 1 supplies
RST OH
Program Counter =

I 3COC pushed onto
the stack.
Control transferred to
B

.j to 0000

0000 '0"'",';00 , /
Instruction 2
RET t
Stack popped into
C
program counter

Device 1 signals an interrupt as the CPU is executing the instruction at 3COB. This instruction is completed.
The program counter remains set to 3COC. and the instruction RST OH supplied by device 1 is executed.
Since this is a call to location zero. 3COC is pushed onto the stack and program control is transferred to
location OOOOH. (This subroutine may perform jumps, calls, or any other operation.) When the RETURN is
executed, address 3COC is popped off the stack and replaces the contents of the program counter, causing
execution to continue at this point.

7-3


WRITING INTERRJPT SUBROUTINES

In general, anI registers or condition bits changed by an Interrupt subroutine must be restored before returning
to the interrurted program, or errors will occur.

For example, . uppose a program is interrupted lust prior to the instruction:

JC LOC

and the carry Jlt equals 1, If the interrupt subroutine happens to reset the carry bit before returning to the
Interrupted pngram, the jump to LOC which should have occurred will not, causing the interrupted program
to produce err Jneous results.

Like any othe subroutine then, any interrupt subroutine should save at least the condition bits and restore them
before perfornling a RETURN operation. (The obVIOUS and most convenient way to do this IS to save the data
In the stack, u,lng PUSH and POP operations.)

Further, the II terrupt enable system is automatically disabled whenever an Interrupt is acknowledged. Except in
special cases, 1herefore, an interrupt subroutine should include an EI instruction somewhere to permit detection
and handling (of future interrupts. One instruction after an EI is executed, the interrupt subroutine may itself be
Interrupted. T lis process may continue to any level, but as long as all pertinent data are saved and restored,
correct progra n execution will continue automatically,

A typical intel rupt subroutine, then, could appear as follows:

Code Operand Comment

PUSH PSW ;SAVE CONDITION BITS AND ACCUMULATOR
EI ;RE-ENABLE INTERRUPTS

;PERFORM NECESSARY ACTIONS TO SERVICE
;THE INTERRUPT

POP PSW ;RESTORE MACHINE STATUS
RET ;RETURN TO INTERRUPTED PROGRAM

74

APPENDIX A. INSTRUCTION SUMMARY
This appendix summarizes the bit patterns and number of time states associated with every 8080 CPU
instruction. The instructions are listed in both mnemonic (alphabetical) and operation code (numerical)
sequence.

When USing this summary, note the following symbology

DDD represents a destination register. SSS represents a source register. Both DDD and SSS are interpreted
as follows:

DDD or SSS Interpretation

000 Register B
001 Register C
010 Register D
011 Register E
100 Register H
101 Register L
110 A memory register or stack pointer or PSW
(flags + accumulator)
111 The accumulator

Instruction execution time equals number of time periods multiplied by the duration of a time period.

A time period may vary from 480 nanoseconds to 2 microseconds on the 8080 or 320 nanoseconds to 2
microseconds on the 8085. Where two numbers of time periods are shown (eq.5/11), it means that the
smaller number of time periods is required if a condition is not met, and the larger number of time periods
is required if the condition IS met.

NUMBER OF TIME PERIODS
MNEMONIC D7 D6 D5 D4 D3 D2 D1 DO
8080 8085

CALL 1 1 0 0 1 1 0 1 17 18 I
!
CC 1 1 0 1 1 1 0 0 11/17 9/18
I
CNC 1 I 0 1 0 1 0 0 11/17 9/18
CZ 1 1 0 0 1 1 0 0 11/17 9/18
CNZ 1 1 0 0 0 1 0 0 11/17 9/18
CP 1 1 1 1 0 1 0 0 11/17 9/18
CM 1 1 1 1 1 1 0 0 11/17 9/18
CPE 1 1 1 0 1 1 0 0 11/17 9/17
CPO 1 1 1 0 0 1 0 0 11/17 9/18
RET 1 1 0 0 1 0 0 1 10 10
RC 1 1 0 1 1 0 0 0 5/11 6/12
RNC 1 1 0 1 0 0 0 0 5/11 6/12
RZ 1 1 0 0 1 0 0 0 5/11 6/12

ALL MNEMONICS©7974, 7975, 7976, 7977 INTEL CORPORATION

A-l

Appendix A. Instruction 5ummary

MNEMONIC D7 D6 D5 D4 D3 D2 D1 DO 8080 8085

RNZ 1 1 0 0 0 0 0 0 5/11 6/12
RP 1 1 1 1 0 0 0 0 5/11 6/12
RM 1 1 1 1 1 0 0 0
I 5/11 6/12
RPE 1 1 1 0 1 0 0 0 5/11 6/12
RPO 1 1 1 0 0 0 0 0 5/11 6/12
RST 1 1 A A A 1 1 1 11 12
IN 1 1 0 1 1 0 1 1 10 10
OUT 1 1 0 1 0 0 1 1 10 10
LXI B 0 0 0 0 0 0 0 1 10 10
LXI D 0 0 0 1 0 0 0 1 10 10
LXI H 0 0 1 0 0 0 0 1 10 10
LXI SP 0 0 1 1 0 0 0 1 10 10
PUSH B 1 1 0 0 0 1 0 1 11 12
PUSH D
PUSH H
1
1
1
1
0
1
1
0
0
0
I 1
1
0
0
1
1
11
11
12
12
PUSH PSW 1 1 1 1 0 1 0 1 11 12
POP B 1 1 0 0 0 0 0 1 10 10
POP D 1 1 0 1 0 0 0 1 10 10
POP H 1 1 1 0 0 0 0 1 10 10
POP PSW 1 1 1 1 0 0 0 1 10 10
STA 0 0 1 1 0 0 1 0 13 13
LDA 0 0 1 1
I 1 0 1 0 13 13
XCHG 1 1 1 0 1 0 1 1 4 4
XTHL 1 1 1 0 0 0 1 1 18 16
SPHL 1 1 1 1 1 0 0 1 5 6
PCHL 1 1 1 0 1 0 0 1 5 6
DAD B 0 0 0 0 1 0 0 1 10 10
DAD D 0 0 0 1 1 0 0 1 10 10
DAD H 0 0 1 0 1 0 0 1 10 10
DAD SP 0 0 I 1 1 0 0 1 10 10
STAX B 0 0 0 0 0 0 1 0 7 7
STAX D 0 0 0 1 0 0 1 0 7 7
LDAX B 0 0 0 0 1 0 1 0 7 7
LDAX D 0 0 0 1 1 0 1 0 7 7
INX B 0 0 0 0 0 0 1 1 5 6
INX D 0 0 0 1 0 0 1 1 5 6
INX H 0 0 1 0 0 0 1 1 5 6
INX SP 0 0 1 1 0 0 1 1 5 6
MOV r1/2 0 1 D D D S S S 5 4
MOV M,r 0 1 1 1 0 S S S 7 7
MOV r,M 0 1 D D D 1 1 0 7 7
HLT 0 1 1 1 0 1 1 0 7 5
MVI r 0 0 D D D 1 1 0 7 7
MVI M 0 0 1 1 0 1 1 0 10 10
INR 0 0 D D D 1 0 0 5 4
DCR 0 0 D D D
ALL MNEMON/CS© 1974,7975,7976, 7977/NTEL CORPORATION
1 0 I 1 5 4

A-2

Appendix A. Instruction Summary

MNEMONIC D7 D D5 D4 D3 D2 D1 DO
6
8080 8085

INR A 0 0 1 1 1 1 0 0 5 4
DCR A 0 0 1 1 1 1 0 1 5 4
INR M 0 0 1 1 0 1 0 0 10 10
DCR M 0 0 1 1 0 1 0 1 10 10
ADD r 1 0 0 0 0 5 5 5 4 4
ADC r 1 0 0 0 1 5 5 5 4 4
SUB r 1 0 0 1 0 5 5 5 4 4
SBB r 1 0 0 1 1 5 5 5 4 4
,AND r 1 0 1 0 0 5 5 5 4 4
XRA r 1 0 1 0 1 5 i 5 5 4 4
I
ORA r 1 0 1 1 0 5 5 5 4 4
CMPr 1 0 1 1 1 5 5 5 4 4
ADD M 1 0 0 0 0 1 1 0 7 7
ADC M 1 0 0 0 1 1 1 0 7 7
SUB M 1 0 0 1 0 1 I 1 0 7 7
5BB M 1 0 0 1 1 1 1 0 7 7
AND M 1 0 1 0 0 1 1 0 7 7
XRA M 1 0 1 0 1 1 1 0 7 7
ORA M 1 0 1 1 0 1 1 0 7 7
CMP M 1 0 1 1 1 1 1 0 7 7
ADI 1 1 0 0 0 1 1 0 7 7
ACI 1 1 0 0 1 1 1 0 7 7
SUI 1 1 0 1 0 1 1 0 7 7
5BI 1 1 0 1 1 1 1 0 7 7
ANI 1 1 1 0 0 1 1 0 7 7
XRI 1 1 1 0 1 1 1 0 7 7
ORI 1 1 1 1 0 1 1 0 7 7
CPI 1 1 1 1 1 1 1 0 7 7
RLC 0 0 0 0 0 1 1 1 4 4
RRC 0 0 0 0 1 1 1 1 4 4
RAL 0 0 0 1 0 1 1 1 4 4
RAR 0 0 0 1 1 1 1 1 4 4
JMP 1 1 0 0 0 0 1 1 10 10
JC 1 1 0 1 1 0 1 0 10 7{10
JNC 1 1 0 1 0 0 1 0 10 7{10
JZ 1 1 0 0 1 0 1 0 10 7{10
JNZ 1 1 0 0 0 0 1 0 10 7{10
JP 1 1 1 1 0 0 1 0 10 7/10
JM 1 1 1 1 1 0 1 0 10 7/10
JPE 1 1 1 0 1 0 1 0 10 7/10
JPO 1 1 1 0 0 0 1 0 10 7{10
DCX B 0 0 0 0 1 0 1 1 5 6
DCX D 0 0 0 1 1 0 1 1 5 6
DCX H 0 0 1 0 1 0 1 1 5 6
DCX 5P 0 0 1 1 1 0 1 1 5 6

ALL MNEMONICS©7974, 7975, 7976, 7977 INTEL CORPORATION A-3

Appendix A. Instruction S!lmmary

MNEMONIC D7 D D D D
6 s 4 3 °2 °1 DO
8080 8085

CMA 0 0 1 0 1 1 1 1 4 4
STC I 0 0 1 1 0 1 1 1 4 4
CMC 0 0 1 1 1 1 1 1 4 4
OAA 0 0 1 0 0 1 1 1 4 4
SHLD 0 0 1 0 0 0 1 0 16 16
LHLD 0 0 1 0 1 0 1 0 16 16
RIM 0 0 1 0 0 0 0 0 - 4
SIM 0 0 1 1 0 0 0 0 - 4
EI 1 1 1 1 1 0 1 1 4 4
DI 1 1 1 1 0 0 1 1 4 4
NOP 0 0 0 0 0 0 0 0 4 4

ALL MNEMONICS ©7~ 74, 7975, 7976. 7977 INTEL CORPORA nON

A4

Appendix A. Instruction Summary

The following is a summary of the instruction set:
8080/85 CPU INSTRUCTIONS IN OPERATION CODE SEQUENCE
OP OP OP OP OP OP
CODE MNEMONIC CODE MNEMONIC CODE MNEMONIC CODE MNEMONIC CODE MNEMONIC CODE MNEMONIC
00 NOP 2B DCX H 56 MOY D,M 81 ADD C AC XRA H D7 RST 2
01 LXI B.D16 2C INR L 57 MOY D,A 82 ADD D AD XRA L D8 RC
02 STAX B 2D DCR L 58 MOY E.B 83 ADD E AE XRA M D9 -
03 INX B 2E MYI L,D8 59 MOY E.C 84 ADD H AF XRA A DA JC Adr
04 INR B 2F CMA SA MOY E,D 85 ADD L BO ORA B DB IN D8
05 DCR B 30 SIM 5B MOY E,E 86 ADD M B1 ORA C DC CC Adr
06 MYI B,D8 31 LXI SPD16 5C MOY E,H 87 ADD A B2 ORA D DD
07 RLC 32 STA Adr 5D MOY E.L 88 ADC B B3 ORA E DE SBI D8
08 - 33 INX SP 5E MOY E,M 89 ADC C B4 ORA H DF RST 3
09 DAD B 34 INR M SF MOY E,A 8A ADC D B5 ORA L EO RPO
OA LDAXB 35 DCR M 60 MOY H,B 8B ADC E B6 ORA M E1 POP H
OB DCX B 36 MVI M,D8 61 MOV H,C 8C ADC H B7 ORA A E2 jPO Adr
OC INR C 37 STC 62 MOV H,D 8D ADC L B8 CMP B E3 XTHL
OD DCR C 38 -- 63 MOV H,E 8E ADC M B9 CMP C E4 CPO Adr
OE MYI C.08 39 DAD SP 64 MOY H,H 8F ADC A BA CMP D E5 PUSH H
OF RRC 3A LDA Adr 65 MOY H,L 8G SUB B BB CMP E E6 ANI D8
10 -- 3B DCX SP 66 MOY H,M 91 SUB C BC CMP H E7 RST 4
11 LXI D,D16 3C INR A 67 MOV H,A 92 SUB D BD CMP L E8 RPE
12 STAX D 3D DCR A 68 MOV L,B 93 SUB E BE CMP M E9 PCHL
13 INX D 3E MYI A,D8 69 MOY L.C 94 SUB H BF CMP A EA IPE Adr
14 INR D 3F CMC 6A MOY L,D 95 SUB L CO RNZ EB XCHG
15 DCR D 40 MOY B.B 6B MOY L,E 96 SUB M C1 POP B EC CPE Adr
16 MYI D,D8 41 MOV B,C 6C MOY L,H 97 SUB A C2 jNZ Adr ED --
17 RAL 42 MOY B.D 6D MOV L,L 98 SBB B C3 IMP Adr EE XRI D8
18 -- 43 MOV B,E 6E MOV L,M 99 SBB C C4 CNZ Adr EF RST 5
19 DAD D 44 MOV B.H 6F MOV L,A 9A SBB D C5 PUSH B FO RP
1A LDAXD 45 MOV B,L 70 MOV M.B 9B SBB E C6 ADI D8 F1 POP PSW
1B DCX D 46 MOY B,M 71 MOV M,C 9C SBB H C7 RST 0 F2 JP Adr
1C INR E 47 MOY B,A 72 MOY M,D 9D SBB L C8 RZ F3 DI
10 DRC E 48 MOY C,B 73 MOV M.E 9E SBB M C9 RET Adr F4 CP Adr
1E MYI E.D8 49 MOY C,C 74 MOV M.H 9F SBB A CA jZ F5 PUSH PSW
1F RAR 4A MOY C.D 75 MOV M.L AO ANA B CB -- F6 ORI D8
20 RIM 4B MOY C,E 76 HLT A1 ANA C CC CZ Adr F7 RST 6
21 LXI H.D16 4C MOV C,H 77 MOY M,A A2 ANA D CD CALL Adr F8 RM
22 SHLD Adr 4D MOY C.L 78 MOV A,B A3 ANA E CE ACI D8 F9 SPHL
23 INX H 4E MOV C,M 79 MOY A.C A4 ANA H CF RST 1 FA jM Adr
24 INR H 4F MOV C.A 7A MOY A.D A5 ANA L DO RNC FB EI
25 DCR H 50 MOV D.B 7B MOV A.E A6 ANA M D1 POP D FC CM Adr
26 MYI H,D8 51 MOV D.C 7C MOV A,H A7 ANA A D2 INC Adr FD --
27 DAA 52 MOY D,D 7D MOV A.L A8 XRA B D3 OUT D8 FE CPI D8
28 -- 53 MOY D.E 7E MOY A.M A9 XRA C D4 CNC Adr FF RST 7
29 DAD H 54 MOY D,H 7F MOY A,A AA XRA D D5 PUSH D
2A LHLD Adr 55 MOY D.L 80 ADD B AB XRA E D6 SUI D8
08 = constant. or logical/arithmetic expressIOn that evaluates 016 constant. or logical/arithmetic expression that evaluates
to an 8 bit data quantity. to a 16 bit data quantity
Adr ~ 16-bit address

ALL MNEMONICS © 1974, 7975, 1976, 7977 INTEL CORPORA TfON
A-5

Appendix A. Instruction :;ummary

Instruction Sct Guidc

Thc following IS I slIl11l11dry of thc IIlstrllclion sct:
,ADD ADI
,A DC ACI
SUB SUI
S3B REGM S SBI DS
,ANA ANI
>RA XRI
eRA ORI
CMP CPI

RLC RAL RRC
RAR CMA DAA
INR}
DCR REGM 8

rlCCUMULATORI FLAGS ISTC CMC HIGH LOW
INXi
MOV REGM 8 ,REGM S[ B I C 1DCXJ REG 16 STACK I POINTER
I [ DIE ~XCHG
RST
LXI REG 16 ,D 16 [ H L
,--------
jMP CALL RET
IC jNCi CC CNCl RC RNCl
I
jZ
jP
jNZ
jM
JPE jPO
J A
CZ
16 CP
CPE
CNZ

CPO
A
CM > 16
J
RZ
RP
RPE
RNZ
RM
RPO
J
LHLDi I
~-" STHDj A16 OUT P8
CONTROL
LDAX BC DE
STAX) , INPUT INSTRUCTIONS
MEMORY OUTPUT
PORTS PORTS RST
LDA~ NOP
STA) A16 HLT
EI
MVI D8 DI
MOV REGM8,REGI~8 --------- PUSH I SIMI
STACK I-E-'-- POP j B,D,H,PSW 8085 ONLY
RIM]
CODE MEANING

REGM 8 The operand l11ay specify one of the 8-bit registers A,B,C,D,E,H, or L or M (a l11el11ol-y
reference via the 16-bit address 111 the Hand L registers). The MOV instruction, which
calls for two operands, can specify M for only one of Its operands_
Designates 8·bit Il11mediatc operand.
Designates a 16·bit address.
Designates an 8·bit port number.
Designates a -16·bit register pair (B&C,D&E,H&L,or SP).
Designates a 16 -bit immediate operand.

ALL MNEMONICS © 1:174, 1975, 7976, 1977 INTEL CORPORA nON

A-6

APPENDIX B. ASSEMBLER DIRECTIVE SUMMARY

Assembler directives are summarIZed alphabetically In this appendix. The following terms are used to describe
the contents of directive fields.

NOTATION

Term Interpretation

Expression Numerical expression evaluated during assembly: must evaluate
to 8 or 16 bits depending on directive issued.

List Series of symbolic values or expreSSions, separated by commas.

Name Symbol name terminated by a space.

Null Field must be empty or an error results.

Oplab Optional label; must be terminated by a colon.

Parameter Dummy parameters are symbols holding the place of actual
parameters (symbolic values or expressIOns) specified elsewhere
in the program.

String Series of any ASCII characters, surrounded by single quote marks.
Single quote within string is shown as two consecutive single quotes.

Text Series of ASCII characters.

Macro definitions and calls allow the use of the special characters listed below.

Character Function

& Ampersand. Used to concatenate symbols.

Angle brackets. Used to delimit text, such as lists, that contain
other delimiters.

Double semicolon. Used before a comment in a macro definition
to prevent inclusion of the comment in each macro expansion.

Exclamation point (escape character). Placed before a delimiter
to be passed as a literal in an actual parameter. To pass a literal
exclamation point, issue'!!.'

% Percent sign. Precedes actual parameters to be evaluated immediately
when the macro is called.


8-1

Appendix B. Assembler 0 :rective Summary

SUMMARY OF DI~.ECTIVES

FORMAT FUNCTION

Label Jpcode Operand(s)

oplab: )8 exp(sl or string(sl Define 8-bit data byte(s). Expressions must evaluate
to one byte.

oplab: )S expression Reserve data storage area of specified length.

oplab: )W exp(sl or string(s) Define 16·blt data word(s). Strings limited to 1-2
characters.

oplab: "LSE null Conditional assembly. Code between ELSE and
ENDIF directives is assembled if expression in IF
clause is FALSE. (See IF.)

oplab: "ND expression Terminate assembler pass. Must be last statement of
program. Program execution starts at 'exp,' if present;
otherWise, at location O.

oplab: "NDIF null Terminate conditional assembly block.

name "QU expression Define symbol 'name' with value 'exp.' Symbol is not
redefi nab Ie.

oplab: iF expression Assemble code between IF and following ELSE or
ENDIF directive if 'exp' is true.

oplab: )RG expression Set location counter to 'expression.'

name ;ET expression Define symbol 'name' with value 'expression.'
Symbol can be redefined.

MACRO DIRECTIV::S

FORMAT FUNCTION

Label Opcode Operand(s)

null I:NDM null Terminate macro definition.

oplab: l:XITM null Alternate terminator of macro definition. (See ENDM.)

oplab: IRP dummy param,<lisO Repeat instruction sequence, substituting one character
form 'list' for 'dummy param' in each iteration.

ALL MNEMONICS©7974, 7975, 7976, 7977 INTEL CORPORATION

8-2

Appendix B. Assembler Directive Summary

FORMAT FUNCTION


oplab: IRPC dummy param,text Repeat instruction sequence, substituting one
character from 'text' for 'dummy param' in each
iteration.

null LOCAL label name(s) Specify label(s) in macro definition to have local
scope.

name MACRO dummy param(s) Define macro 'name' and dummy parameter(s) to be
used in macro definition.

oplab: REPT expression Repeat REPT block 'expression' times.

RELOCATION DIRECTIVES

FORMAT FUNCTION


oplab: ASEG null Assemble subsequent instructions and data in the
absol ute mode.

oplab: CSEG boundary specification Assemble subsequent instructions and data In the
relocatable mode using the code location counter.

oplab: DSEG boundary specification Assemble subsequent instructions and data in the
relocatable mode using the data location counter.

oplab: EXTRN name(s) Identify symbols used in this program module but
defined in a different module.

oplab: NAME module-name ASSigns a name to the program module.

oplab: PUBLIC name(s) Identify symbols defined in this module that are to
be available to other modules.

oplab: STKLN expression Specify the number of bytes to be reserved for the
stack for this module.

ALL MNEMONICS©7974, 7975, 7976, 7977 INTEL CORPORA TlON

B-3

APPENDIX C. ASCII CHARACTER SET

ASCII CODES
The 8080 and 8085 usc the seven-bit ASCII code, with the high-order eighth bit
(parity bitl always reset.

, GRAPHIC OR ASCII GRAPHIC OR ASCII GRAPHIC OR ASCII
CONTROL (HEXADECIMAL) CONTROL (HEXADECIMAL) CONTROL (HEXADECIMAL)
NUL 00 + 2B V 56
SOH 01 2C W 57
STX 02 2D X 58
ETX 03 2E Y 59
EaT 04 I 2F Z 5A
ENQ 05 0 30 [ 5B
ACK 06 1 31 5C
BEL 07 2 32 1 5D
BS 08 3 33 i (t) 5E
HT 09 4 34 (+-) 5F
LF OA 5 35 , 60
VT OB 6 36 a 61
FF OC 7 37 b 62
CR OD 8 38 c 63
SO OE 9 39 d 64
SI OF 3A e 65
DLE 10 3B f 66
DCl (X-ON) 11 < 3C 9 67
DC2 (TAPE) 12 3D h 68
DC3 (X-OFF) 13 > 3E I 69
DC4 (+Afl8 14 3F J 6A I
NAK 15 @ 40 k 6B
SYN 16 A 41 I 6C
ETB 17 B 42 m 6D
CAN 18 C 43 n 6E
EM 19 D 44 0 6F
SUB lA E 45 P 70
ESC lB F 46 q 71
FS lC G 47 r 72
GS 10 H 48 s 73
RS lE I 49 t 74
US IF J 4A u 75
SP 20 K 4B v 76
21 L 4C w 77
22 M 4D x 78
# 23 N 4E v 79
$ 24 a 4F z 7A
I
% 25 P 50 7B
26 Q 51 I 7C
&
27 R 52
, (ALT MODE)
I 7D
28 S 53 ~
7E
29 T 54 DEL (RUB OUT) 7F
2A U 55

C-1

APPENDIX D.

BINARY -DECIMAL-HEXADECIMAL CONVERSION TABLES.

D-l

Appendix D. BinarVMDecinal-Hexadecimal Conversion Tables

P<)WERS OF TWO
n ·n
2 n 2
1 o 1.0
2 1 0.5
4 2 0.25
8 3 0.125
16 4 0.062 5
32 5 0.031 25
64 6 0.015 625
128 7 0.007 812 5
256 8 0.003 906 25
512 9 0.001 953 125
1 024 10 0.000 976 562 5
2 Cl48 11 0.000 488 281 25
4 096 12 0.000 244 140 625
8 192 13 0.000 122 070 312 5
16 384 14 0.000 061 035 156 25
32 768 15 0.000 030 517 578 125
65 536 16 0.000 015 258 789 062 5
131 072 17 0.000 007 629 394 531 25
262 144 18 0.000 003 814 697 265 625
524 288 19 0.000 001 907 348 632 812 5
1 048 576 20 0.000 000 953 674 316 406 25
2 097 152 21 0.000 000 476 837 158 203 125
4 194 304 22 0.000 000 238 418 579 101 5625
8 388 308 23 0.000 000 119 209 289 550 781 25

16 7?7 216 24 0.000 000 059 6Cl4 644 77 5 390 625
33 554 ~32 25 0.000 000 029 802 322 387 695 312 5
67 108 364 26 0000 000 014 901 161 193 847 656 25
134 217 728 27 0.000 000 007 450 580 596 923 828 125
268 435 ~56 28 0.000 000 003 725 290 298 461 914 062 5
536 870 :l12 29 0.000 000 001 862 645 149 230 957 031 25
1 073 741 324 30 0.000 000 000 931 322 574 615 478 515 625
2 147 483 548 31 0.000 000 000 465 661 287 307 739 257 812 5
4 294 967 296 32 0000 000 000 232 830 643 653 869 628 906 25
8 589 934 592 33 0000 000 000 116 415 321 826 934 814 453 125
17 179 869 184 34 0000 000 000 058 207 660 913 467 407 226 562 5
34 359 738 368 35 0.000 000 000 029 103 830 456 733 703 613 281 25
68 719 476 736 36 0.000 000 000 014 551 915 228 366 851 806 640 625
137 438 953 ~72 37 0.000 000 000 007 275 957 614 183 425 903 320 312 5
274 877 906 :l44 38 0.000 000 000 003 637 978 807 091 712 951 660 156 25
549 755 813 388 39 0.000 000 000 001 818 989 403 545 856 475 830 078 125
1 099 511 627 776 40 0.000 000 000 000 909 494 701 772 928 237 915 039 062 5
2 199 023 255 55241 0.000 00.0 000 000 4,,4 747 350 886 464 118957 519531 25
4 398 046 511 104 42 0.000 000 000 000 227 373 675 443 232 059 478 759 765 625
8 796 093 022 208 43 0.000 000 000 000 113 686 837 721 616 029 739 379 882 812 5
17 592 186 044 41644 0.000 000 000 000 056 843 418 860 808 014 869 689 941 406 25
35 184 372 088 332 45 0.000 000 000 000 028 421 709 430 404 007 434 844 970 703 125
70 368 744 177 56446 0.000 000 000 000 014 210 854 715202 003 717 422 485 351 5625
140 737 488 355 328 47 0.000 000 000 000 007 105427 357 601 001 858 711 242675 781 25
281 474 976 710 556 48 0.000 000 000 000 003 552 713 678 800 500 929 355 621 337 890 625
562 949 953 421 312 49 0.000 000 000 000 001 776 356 839 400 250 464 677 810 668 945 312 5
1 125899906842 524 50 0.000 000 000 000 000 888 178419 700 125 232 338 905 3Cl4 472 656 25
2 251 799 813 685 248 51 0.000 000 000 000 000 444 089 209 850 062 616 169 452 667 236 328 125
4 503 599 627 370 496 52 0.000 000 000 000 000 222 044 604 925 031 308 084 726 333 618 164 062 5
9 007 199 254 740 992 53 0.000 000 000 000 000 111 022 302 462 515 654 042 363 166 809 082 031 25
18 014 398 509 481 98454 0.000 000 000 000 000 055511 151 231 257827 021 181 583404 541 015625
36 028 797 018 963 968 55 0.000 000 000 000 000 027 755 575 615 628 913 510 590 791 702 270 507 812 5
72 057 594 037 927 936 56 0.000 000 000 000 000 013 877 787 807 814 456 755 295 395 851 135 253 906 25
144 115 188 075 855 872 57 0.000 000 000 000 000 006 938 893 903 907 228 377 647 697 925 567 676 950 125
288 230 376 151 711 744 58 0.000 000 000 000 000 003 469 446 951 953 614 188 823 848 962 783 813 476 562 5
576 460 752 303 423 488 59 0.000 000 000 000 000 001 734 723 475 976 807 094 411 924 481 391 906 738 281 25
1 152 921 504 606 846 976 60 0000 000 000 000 000 000 867 361 737 988 403 547 205 962 240 695 953 369 140 625
2 305 843 009 213 693 952 61 0.000 000 000 000 000 000 433 680 868 994 201 773 602 981 120 347 976 684 570 312 5
4 611 686 018 427 387 904 62 0.000 000 000 000 000 000 216 840 434 497 100 886 801 490 560 173 988 342 285 156 25
9 223 372 036 854 775 808 63 0.000 000 000 000 000 000 108 420 217 248 550 443 400 745 280 086 994 171 142 578 125

D-2

Appendix D. Binary~Decimal-Hexadecimal Conversion Tables

POWERS OF 16 (IN BASE 10)
16" 16'"
1 0 0.10000 00000 00000 00000 X 10
16 1 0.62500 00000 00000 00000 X 10- 1
256 2 0.39062 50000 00000 00000 X 10- 2
4 096 3 0.24414 06250 00000 00000 X 10- 3
65 536 4 0.15258 78906 25000 00000 X 10-4
1 048 576 5 0.95367 43164 06250 00000 X 10-6
16 777 216 6 0.59604 64477 53906 25000 X 10- 7
268 435 456 7 0.37252 90298 46191 40625 X 10-8
4 294 967 296 8 0.23283 06436 53869 62891 x 10-9
68 719 476 736 9 0.14551 91522 83668 51807 x 10- 10
1 099 511 627 776 10 0.90949 47017 72928 23792 X 10- 12
17 592 186 044 416 11 0.56843 41886 08080 14.870 X 10- 13
281 474 976 710 656 12 0.35527 13678 80050 09294 X 10- 14
4 503 599 627 370 496 13 0.22204 46049 25031 30808 X 10- 15
72 057 594 037 927 936 14 0.13877 78780 78144 56755 X 10- 16
152 921 504 606 846 976 15 0.86736 17379 88403 54721 X 10- 18

POWERS OF 10 (IN BASE 16)

10" 10'"
1 0 1.0000 0000 0000 0000
A 1 0.1999 9999 9999 999A
64 2 0.28F5 C28F 5C28 F5C3 x 16- 1
3E8 3 0.4189 374B e6A7 EF9E x 16 -2
2710 4 0.68oB 8BAC 710C B296 x 16- 3
1 86AO 5 0.A7C5 AC47 lB47 8423 x 16- 4
F 4240 6 0.10C6 F7AO B5EO 8037 x 16-4
98 9680 7 0.lA07 F29A BCAF 4858 X 16- 5
5F5 El00 8 0.2AF3 lOC4 6118 73BF x 16-6
3B9A CAOO 9 0.44BB 2FAO 9B5A 52CC x 16- 7
2 540B E400 10 0.6oF3 7F67 SEF6 EAoF x 16-8
17 4876 E800 11 O.AFEB FFOB CB24 AAFF x 16- 9
E8 o4A5 1000 12 0.1197 9981 20EA 1119 x 16-9
918 4E72 AOOO 13 0.lC25 C268 4976 81C2 X 16- 10
5AF3 107A 4000 14 0.2009 3700 4257 3604 x 16- 11
3 807E A4C6 8000 15 0.480E BE7B 9058 5660 X 16- 12
23 8652 6FCl 0000 16 0.734A CA5F 6226 FOAE x 16- 13
163 4578 508A 0000 17 0.B877 AA32 36A4 B449 x 16- 14
oEO B6B3 A764 0000 18 0.1272 5001 0243 ABAl X 16- 14
8AC7 2304 89E8 0000 19 0.1083 C94F B602 AC35 X 16- 15

D-3

Appendix D. Binary-Declllal-Hexadecimal ConversIon Tables

HEXADECIMAL-DECIMAL INTEGER CONVERSION

The table below provide! for direct conversions between hexadecimal Integers In the range O-FFF and decimal integers In the
range 0-4095. For conVHSlon of larger Integers, the table values may be added to the following figures:

Hexadecimal Decimal Hexadecimal Decimal
01000 4096 20000 131072
02000 8192 30000 196608
03000 12288 40000 262144
04000 16384 50000 327 680
05000 20480 60000 393216
06000 24576 70000 458752
07000 28672 80000 524288
08000 32768 90000 589824
09000 36864 AO 000 655360
OA 000 40960 80000 720896
OB 000 45056 CO 000 786432
oe 000 49152 DO 000 851 968
OD 000 53248 EO 000 917504
OE 000 57344 FO 000 983040
OF 000 61440 100000 1048576
10000 65536 200000 2097152
11 000 69632 300000 3 145728
12000 73728 400000 4194304
13000 77 824 500000 5242880
14000 81920 600000 6291456
15000 86016 700000 7340032
16000 90112 800000 8388608
17000 94208 900000 9437184
18000 98304 AOO 000 10485760
19000 102400 BOO 000 11 534336
lAOOO 106496 COO 000 12 582912
lB 000 110592 DOO 000 13631488
leOOO 114688 EOO 000 14680064
10 000 118784 FOO 000 15728640
lE 000 122 880 1000000 16777216
1F 000 126976 2000000 33554432

0 1 2 3 4 5 6 7 8 9 A B e D E F

000 0000 0001 0002 0003 0004 0005 0006 0007 OOOB 0009 0010 0011 0012 0013 0014 0015
010 0016 0017 0018 0019 0020 0021 0022 0023 0024 0025 0026 0027 0028 0029 0030 0031
020 0032 0033 0034 0035 0036 0037 0038 0039 0040 0041 0042 0043 0044 0045 0046 0047
030 0048 0049 0050 0051 0052 0053 0054 0055 0056 0057 0058 0059 0060 0061 0062 0063

040 0064 0065 0066 0067 0068 0069 0070 0071 0072 0073 0074 0075 0076 0077 0078 0079
050 0080 0081 0082 0083 0084 0085 00B6 0087 0088 0089 0090 0091 0092 0093 0094 0095
060 0096 0097 0098 0099 0100 0101 0102 0103 0104 0105 0106 0107 0108 0109 0110 0111
070 0112 0113 o 14 0115 0116 0117 0118 0119 0120 0121 0122 0123 0124 0125 0126 0127

080 0128 0129 030 0131 0132 0133 0134 0135 0136 0137 0138 0139 0140 0141 0142 0143
090 0144 0145 046 0147 0148 0149 0150 0151 0152 0153 0154 0155 0156 0157 0158 0159
OAO 0160 0161 062 0163 0164 0165 0166 0167 0168 0169 0170 0171 0172 0173 0174 0175
OBO 0176 0177 078 0179 0180 0181 0182 0183 0184 0185 0186 0187 0188 0189 0190 0191

oeo 0192 0193 094 0195 0196 0197 0198 0199 0200 0201 0202 0203 0204 0205 0206 0207
ODO 0208 0209 0:!10 0211 0212 0213 0214 0215 0216 0217 0218 0219 0220 0221 0222 0223
OEO 0224 0225 0:!26 0227 0228 0229 0230 0231 0232 0233 0234 0235 0236 0237 0238 0239
OFO 0240 0241 0:!42 0243 0244 0245 0246 0247 0248 0249 0250 0251 0252 0253 0254 0255

D-4

Appendix D. Binary-Decimal-Hexadecimal Conversion Tables

HEXADECIMAL-DECIMAL INTEGER CONVERSION (Cant'dl
0 1 2 3 4 5 6 7 8 9 A B C D E F
100 0256 0257 0258 0259 0260 0261 0262 0263 0264 0265 0266 0267 0268 0269 0270 0271
110 0272 0273 0274 0275 0276 0277 0278 0279 0280 0281 0282 0283 0284 0285 0286 0287
120 0288 0289 0290 0291 0292 0293 0294 0295 0296 0297 0298 0299 0300 0301 0302 0303
130 0304 0305 0306 0307 0308 0309 0310 0311 0312 0313 0314 0315 0316 0317 0318 0319
140 I 0320 0321 0322 0323 0324 0325 0326 0327 0328 0329 0330 0331 0331 0333 0334 0335
150 0336 0337 0338 0339 0340 0341 0342 0343 0344 0345 0346 0347 0348 0349 0350 0351
160 0352 0353 0354 0355 0356 0357 0358 0359 0360 0361 0362 0363 0364 0365 0366 0367
170 0368 0369 0370 0371 0372 0373 0374 0375 0376 0377 0378 0379 0380 0381 0382 0383
180 0384 0385 0386 0387 038l:l 0389 0390 0391 0392 0393 0394 0395 0396 0397 0398 0399
190 0400 0401 0402 0403 0404 0405 0406 0407 0408 0409 0410 0411 0412 0413 0414 0415
lAO 0416 0417 0418 0419 0420 0421 0422 0423 0424 0425 0426 0427 0428 0429 0430 0431
lBO 0432 0433 0434 0435 0436 0437 0438 0439 0440 0441 0442 0443 0444 0445 0446 0447

lCO
lDO
I 0448
0464
0449
0465
0450 0451
0466 0467
0452
0468
0453
0469
0454
0470
0455
0471
0456
0472
0457
0473
0458
0474
0459
0475
0460
0476
0461
0477
0462
0478
0463
0479
lEO 0480 0481 0482 0483 0484 0485 0486 0487 0488 0489 0490 0491 0492 0493 0494 0495
lFO 0496 0497 0498 0499 0500 0501 0502 0503 0504 0505 0506 050"/ 0508 0509 0510 0511

200 0512 0513 0514 0515 0516 0517 0518 0519 0520 0521 0522 0523 0524 0525 0526 0527
210 I 05280529 0530 0531 0532 0533 0534 0535 0536 0537 0538 0539 0540 0541 0542 0543
220 0544 0545 0546 0547 0548 0549 0550 0551 0552 0553 0554 0555 0556 0557 0558 0559
230 0560 0561 0562 0563 0564 0565 0566 0567 0568 0569 0570 0571 0572 0573 0574 0575
240 0576 0577 0578 0579 0580 0581 0582 0583 0584 0585 0586 0587 0588 0589 0590 0591
250 0592 0593 0594 0595 0596 0597 0598 0599 0600 0601 0602 0603 0604 0605 0606 0607
260 0608 0609 0610 0611 0612 0613 0614 0615 0616 0617 0618 0619 0620 0621 0622 0623
270 0624 0625 0626 0627 0628 0629 0630 0631 0632 0633 0634 0635 0636 0637 0638 0639
280 0640 0641 0642 0643 0644 0645 0646 0647 0648 0649 0650 0651 0652 0653 0654 0655
290 0656 0657 0658 0659 0660 0661 0662 0663 0664 0665 0666 0667 0668 0669 0670 0671
2AO 0672 0673 0674 0675 0676 0677 0678 0679 0680 0681 0682 0683 0684 0685 0686 0687
2BO 0688 0689 0690 0691 0692 0693 0694 0695 0696 0697 0698 0699 0700 0701 0702 0703
2CO 0704 0705 0706 0707 0708 0709 0710 0711 0712 0713 0714 0715 0716 0717 0718 0719
2DO 0720 0721 0722 0723 0724 0725 0726 0727 0728 0729 0730 0731 0732 0733 0734 0735
2EO 0736 0737 0738 0739 0740 0741 0742 0743 0744 0745 0746 0747 0748 0749 0750 0751
2FO 0752 0753 0754 0755 0756 0757 0758 0759 0760 0761 0762 0763 0764 0765 0766 0767

300 0768 0769 0770 0771 0772 0773 0774 0775 0776 0777 0778 0779 0780 0781 0782 0783
310 0784 0785 0786 0787 0788 0789 0790 0791 0792 0793 0794 0795 0796 0797 0798 0799
320 0800 0301 0802 0803 0804 0805 0806 0807 0808 0809 0810 0811 0812 0813 0814 0815
330 0816 0817 0818 0819 0820 0821 0822 0823 0824 0825 0826 0827 0828 0829 0830 0831
340 0832 0833 0834 0835 0836 0837 0838 0839 0840 0841 0842 0843 0844 0845 0846 0847
350 0848 0849 0850 0851 0852 0853 0854 0855 0856 0857 0858 0859 0860 0861 0862 0863
360 0864 0865 0866 0867 0868 0869 0870 0871 0872 0873 0874 0875 0876 0877 0878 0879
370 0880 0881 0882 0883 0884 0885 0886 0887 0888 0889 0890 0891 0892 0893 0894 0895
380 0896 0897 0898 0899 0900 0901 0902 0903 0904 0905 0906 0907 0908 0909 0910 0911
390 0212 0913 0914 0915 0916 0917 0918 0919 0920 0921 0922 0923 0924 0925 0926 0927
3AO 0928 0929 0930 0931 0932 0933 0934 0935 0936 0937 0938 0939 0940 0941 0942 0943
3BO 0944 0945 0946 0947 0948 0949 0950 0951 0952 0953 0954 0955 0956 0957 0958 0959
j3CO 0960 0961 0962 0963 0964 0965 0966 0967 0968 0969 0970 0971 0972 0973 0974 0975
3DO 0976 0977 0978 0979 0980 0981 0982 0983 0984 0985 0986 0987 0988 0989 0990 0991
3EO 0992 0993 0994 0995 0996 0997 0998 0999 1000 1001 1002 1003 1004 1005 1006 1007
1
i 3FO 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023

D-5

Appendix O. Binarv-Oet Imal~HexadecimaJ Conversion Tables

HEXADECIMAL-DECIMAL INTEGER CONVERSION (Cont'd)
I
0 1 2 3 4 5 6 7 8 9 A B C 0 E F
400 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039
410 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055
420 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071
430 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087
440 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103
450 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119
460 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135
470 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151
480 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167
490 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183
4AO 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199
4BO 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215
4CO 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231
400 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247
4EO 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263
4FO 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279

500 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295
510 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1'306 1307 1308 1309 1310 1311
520 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327
530 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343
540 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359
550 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375
560 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391
570 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407
580 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423
590 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439
5AO 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455
5BO 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471
5CO 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487
500 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503
5EO 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519
5FO 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535
600 1536 1537 1538 1539 1540 1541 154~ 1543 1544 1545 1546 1547 1548 1549 1550 1551
610 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567
620 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583
630 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599
640 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615
650 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631
660 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647
670 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663
680 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679
690 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695
6AO 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711
680 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727
6CO 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743
600 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759
6EO 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775
6FO 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791
D-6

Appendix D. Binarv-Decimal-Hexadecimal Conversion Tables

0 1 2 3 4 5 6 7 8 9 A B C 0 E F
700 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807
710 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823
720 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839
! 730 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855
I
740 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871
750 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887
760 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903
770 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1911j 1917 1918 1919
780 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935
790 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1
7AO 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967
7BO 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983
7CO 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
700 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
7EO 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031
7FO 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047

800 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063
810 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079
820 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095
830 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111
840 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127
.850 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143
860 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159
870 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175
880 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190 2191
890 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207
8AO 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223
8BO 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239
8CO 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255
800 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271
8EO 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287
8FO 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298 2299 2300 2301 2302 2303

900 2304 2305 2306 2307 2308 2309 2310 2311 2312 2313 2314 2315 2316 2317 2318 2319
910 2320 2321 2322 2323 2324 2325 2326 2327 2328 2329 2330 2331 2332 2333 2334 2335
920 2336 2337 2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351
930 I 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363 2364 2365 2366 2367
1
940 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 2381 2382 2383
950 2384 2385 2386 2387 2388 2389 2390 2391 2392 2393 2394 2395 2396 2397 2398 2399
960 2400 2401 2402 2403 2404 2405 2406 2407 2408 2409 2410 2411 2412 2413 2414 2415
970 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431

980 2432 2433 2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447
990 2448 2449 2450 2451 2452 2453 2454 2455 2456 2457 2458 2459 2460 2461 2462 2463
9AO 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479
980 2480 2481 2482 2483 2484 2485 2486 2487 2488 2489 2490 2491 2492 2493 2494 2495

9CO 2496 2497 2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509 2510 2511
900 2512 2513 2514 2515 2516 2517 2518 2519 2520 2521 2522 2523 2524 2525 2526 2527
9EO 2528 2529 2530 2531 2532 2533 2534 2535 2536 2537 2538 2539 2540 2541 2542 2543
9FO 2544 2545 2546 2547 2548 2549 2550 2551 2552 2553 2554 2555 2556 2557 2558 2559
0-7

Appendix D. Binary-Declmal-Hexadeclmal Conversion Tables

HEXADECIMAL·DECIMAL INTEGER CONVERSION (Cont'dl
0 1 2 3 4 5 6 7 8 9 A 8 C D E F
Aoo 2560 2561 2562 2563 2564 2565 2566 2567 2568 2569 2570 2571 2572 2573 2574 2575
Al0 2576 2577 2578 2579 2580 2581 2582 2583 2584 2585 2586 2587 2588 2589 2590 2591
A20 2592 2593 2594 2595 2596 2597 2598 2599 2600 2601 2602 2603 2604 2605 2606 2607
A30 2608 2609 2610 2611 2612 2613 2614 2615 2616 2617 2618 2619 2620 2621 2622 2623
A40 2624 2625 2626 2627 2628 2629 2630 2631 2632 2633 2634 2635 2636 2637 2638 2639
A50 2640 2641 2642 2643 2644 2645 2646 2647 2648 2649 2650 2651 2652 2653 2654 2655
A60 2656 2657 2658 2659 2660 2661 2662 2663 2664 2665 2666 2667 2668 2669 2670 2671
A70 2672 2673 2674 2675 2676 2677 2678 2679 2680 2681 2682 2683 2684 2685 2686 2687
A80 2688 2689 2690 2691 2692 2693 2694 2695 2696 2697 2698 2699 2700 2701 2702 2703
A90 2704 2705 2706 2707 2708 2709 2710 2711 2712 2713 2714 2715 2716 2717 2718 2719
AAO 2720 2721 2722 2723 2724 2725 2726 2727 2728 2729 2730 2731 2732 2733 2734 2735
ABO 2736 2737 2738 2739 2740 2741 2742 2743 2744 2745 2746 2747 2748 2749 2750 2751

ACO 12752 2753 2754 2755 2756 2757 2758 2759 2760 4761 2762 2763 2764 2765 2766 2767
ADO I 2768 2769 2770 2771 2772 2773 2774 2775 2776 2777 2778 2779 2780 2781 2782 2783
AEO 2784 2785 2786 2787 2788 2789 2790 2791 2792 2793 2794 2795 2796 2797 2798 2799
AFO 2800 2801 2802 2803 2804 2805 2806 2807 2808 2809 2810 2811 2812 2813 2814 2815

BOO 2816 2817 2818 2819 2820 2821 2822 2823 2824 2825 2826 2827 2828 2829 2830 2831
Bl0 2832 2833 2834 2835 2836 2837 2838 2839 2840 2841 2842 2843 2844 2845 2846 2847
B20 2848 2849 2850 3851 2852 2853 2854 2855 2856 2857 2858 2859 2860 2861 2862 2863
B30 2864 2865 2866 2867 2868 2869 2870 2871 2872 2873 2874 2875 2876 2877 2878 2879
B40 2880 2881 2882 2883 2884 2885 2866 2887 2888 2889 2890 2891 2892 2893 2894 2895
B50 2896 2897 2898 2899 2900 2901 2902 2903 2904 2905 2906 2907 2908 2909 2910 2911
B60 2912 2913 2914 2915 2916 2917 2918 2919 2920 2921 2922 2923 2924 2925 2926 2927
B70 2928 2929 2930 2931 2932 2933 2934 2935 2936 2937 2938 2939 2940 2941 2942 2943
B80 2944 2945 2946 2947 2948 2949 2950 2951 2952 2953 2954 2955 2956 2957 2958 2959
B90 2960 2961 2962 2963 2964 2965 2966 2967 2968 2969 2970 2971 2972 2973 2974 2975
BAO 2976 2977 2978 2979 2980 2981 2982 2983 2984 2985 2986 2987 2988 2989 2990 2991
BBO 2992 2993 2994 2995 2996 2997 2998 2999 3000 3001 3002 3003 3004 3005 3006 3007
BCO 3008 3009 3010 3011 3012 3013 3014 3015 3016 3017 3018 3019 3020 3021 3022 3023
BDO 3024 3025 3026 3027 3028 3029 3030 3031 3032 3033 3034 3035 3036 3037 3038 3039
BEO 3040 3041 3042 3043 3044 3045 3046 3047 3048 3049 3050 3051 3052 3053 3054 3055
BFO 3056 3057 3058 3059 3060 3061 3062 3063 3064 3065 3066 3067 3068 3069 3070 3071
---
COO 3072 3073 3074 3075 3076 3077 3078 3079 3080 3081 3082 3083 3084 3085 3086 3087
Cl0 3088 3089 3090 3091 3092 3093 3094 3095 3096 3097 3098 3099 3100 3101 3102 3103
C20 3104 3105 3106 3107 3108 3109 3110 3111 3112 3113 3114 3115 3116 3117 3118 3119
C30 3120 3121 3122 3123 3124 3125 3126 3127 3128 3129 3130 3131 3132 3133 3134 3135
C40 3136 3137 3138 3139 3140 3141 3142 3143 3144 3145 3146 3147 3148 3149 3150 3151
C50 3152 3153 3154 3155 3156 3157 3158 3159 3160 3161 3162 3163 3164 3165 3166 3167
C60 3168 3169 3170 3171 3172 3173 3174 3175 3176 3177 3178 3179 3180 3181 3182 3183
C70 3184 3185 3186 3187 3188 3189 3190 3191 3192 3193 3194 3195 3196 3197 3198 3199
C80 3200 3201 3202 3203 3204 3205 3206 3207 3208 3209 3210 3211 3212 3213 3214 3215
C90 3216 3217 3218 3219 3220 3221 3222 3223 3224 3225 3226 3227 3228 3229 3230 3231
CAO 3232 3233 3234 3235 3236 3237 3238 3239 3240 3241 3242 3243 3244 3245 3246 3247
CBO 3248 3249 3250 3251 3252 3253 3254 3255 3256 3257 3258 3259 3260 3261 3262 3263
CCO 3264 3265 3266 3267 3268 3269 3270 3271 3272 3273 3274 3275 3276 3277 3278 3279
CDO 3280 3281 3282 3283 3284 3285 3286 3287 3288 3289 3290 3291 3292 3293 3294 3295
CEO 3296 3297 3298 3299 3300 3301 3302 3303 3304 3305 3306 3307 3308 3309 3310 3311
CFO 3312 3313 3314 3315 3316 3317 3318 3319 3320 3321 3322 3323 3324 3325 3326 3327

D-8

Appendix D. Binary-Declmal-Hexadecimal ConverSion Tables


0 1 2 3 4 5 6 7 8 9 A B C 0 E F
000 3328 3329 3330 3331 3332 3333 3334 3335 3336 3337 3338 3339 3340 3341 3342 3343
010 3344 3345 3346 3347 3348 3349 3350 3351 3352 3353 3354 3355 3356 3357 3358 3359
020 3360 3361 3362 3363 3364 3365 3366 3367 3368 3369 3370 3371 3372 3373 3374 3375
030 3376 3377 3378 3379 3380 3381 3382 3383 3384 3385 3386 3387 3388 3389 3390 3391
040 3392 3393 3394 3395 3396 3397 3398 3399 3400 3401 3402 3403 3404 3405 3406 3407
050 3408 3409 3410 3411 3412 3413 3414 3415 3416 3417 3418 3419 3420 3421 3422 3423
060 3424 3425 3426 3427 3428 3429 3430 3431 3432 3433 3434 3435 3436 3437 3438 3439
070 3440 3441 3442 3443 3444 3445 3446 3447 3448 3449 3450 3451 3452 3453 3454 3455
080 3456 3457 3458 3459 3460 3461 3462 3463 3464 3465 3466 3467 3468 3469 3470 3471
090 3472 3473 3474 3475 3476 3477 3478 3479 3480 3481 3482 3483 3484 3485 3486 3487
OAO 3488 3489 3490 3491 3492 3493 3494 3495 3496 3497 3498 3499 3500 3501 3502 3503
OBO 3504 3505 3506 3507 3508 3509 3510 3511 3512 3513 3514 3515 3516 3517 3518 3519
OCO 3520 3521 3522 3523 3524 3525 3526 3527 3528 3529 3530 3531 3532 3533 3534 3535
000 3536 3537 3538 3539 3540 3541 3542 3543 3544 3545 3546 3547 3548 3549 3550 3551
OEO 3552 3553 3554 3555 3556 3557 3558 3559 3560 3561 3562 3563 3564 3565 3566 3567
OFO 3568 3569 3570 3571 3572 3573 3574 3575 3576 3577 3578 3579 3580 3581 3582 3583
EOO 3584 3585 3586 3587 3588 3589 3590 3591 3592 3593 3594 3595 3596 3597 3598 3599
El0 3600 3601 3602 3603 3604 3605 3606 3607 3608 3609 3610 3611 3612 3613 3614 3615
E20 3616 3617 3618 3619 3620 3621 3622 3623 3624 3625 3626 3627 3E528 3629 3630 3631
E30 3632 3633 3634 3635 3636 3637 3638 3639 3640 3641 3642 3643 3644 3645 3646 3647
E40 3648 3649 3650 3651 3652 3653 3654 3655 3656 3657 3658 3659 3660 3661 3662 3663
E50 3664 3665 3666 3667 3668 3669 3670 3671 3672 3673 3674 3675 3676 3677 3678 3679
E60 3680 3681 3682 3683 3684 3685 3686 3687 3688 3689 3690 3691 3692 3693 3694 3695
E70 3696 3697 3698 3699 3700 3701 3702 3703 3704 3705 3706 3707 3708 3709 3710 3711
E80 3712 3713 3714 3715 3716 3717 3718 3719 3720 3721 3722 3723 3724 3725 3726 3727
E90 3728 3729 3730 3731 3732 3733 3734 3735 3736 3737 3738 3739 3740 3741 3742 3743
EAO 3744 3745 3746 3747 3748 3749 3750 3751 3752 3753 3754 3755 3756 3757 3758 3759
EBO 3760 3761 3762 3763 3764 3765 3766 3767 3768 3769 3770 3771 3772 3773 3774 3775
ECO 3776 3777 3778 3779 3780 3781 3782 3783 3784 3785 3786 3787 3788 3789 3790 3791
EOO 3792 3793 3794 3795 3796 3797 3798 3799 3800 3801 3802 3803 3804 3805 3806 3807
EEO 3808 3809 3810 3811 3812 3813 3814 3815 3816 3817 3818 3819 3820 3821 3822 3823
EFO 3824 3825 3826 3827 3828 3829 3830 3831 3832 3833 3834 3835 3836 3837 3838 3839
FOO 3840 3841 3842 3843 3844 3845 3846 3847 3848 3849 3850 3851 3852 3853 3854 3855
FlO 3856 3857 3858 3859 3860 3861 3862 3863 3864 3865 3866 3867 3868 3869 3870 3871
F20 3872 3873 3874 3875 3876 3877 3878 3879 3880 3881 3882 3883 3884 3885 3886 3887
F30 3888 3889 3890 3891 3892 3893 3894 3895 3896 3897 3898 3899 3900 3901 3902 3903
F40 3904 3905 3906 3907 3908 3909 3910 3911 3912 3913 3914 3915 3916 3917 3918 3919
F50 3920 3921 3922 3923 3924 3925 3926 3927 3928 3929 3930 3931 3932 3933 3934 3935
F60 3936 3937 3938 3939 3940 3941 3942 3943 3944 3945 3946 3947 3948 3949 3950 3951
F70 3952 3953 3954 3955 3956 3957 3958 3959 3960 3961 3962 3963 3964 3965 3966 3967
F80 3968 3969 3970 3971 3972 3973 3974 3975 3976 3977 3978 3979 3980 3981 3982 3983
F90 3984 3985 3986 3987 3988 3989 3990 3991 3992 3993 3994 3995 3996 3997 3998 3999
FAO 4000 4001 4002 4003 4004 4005 4006 4007 4008 4009 4010 4011 4012 4013 4014 4015
FBO 4016 4017 4018 4019 4020 4021 4022 4023 4024 4025 4026 4027 4028 4029 4030 4031
FCO 4032 4033 4034 4035 4036 4037 4038 4039 .4040 4041 4042 4043 4044 4045 4046 4047
FOO 4048 4049 4050 4051 4052 4053 4054 4055 4056 4057 4058 4059 4060 4061 4062 4063
FEO 4064 4065 4066 4067 4068 4069 4070 4071 4072 4073 4074 4075 4076 4077 4078 4079
FFO 4080 4081 4082 4083 4084 4085 4086 4087 4088 4089 4090 4091 4092 4093 4094 4095
0-9

INDEX

Absolute symbols 2-11. 2-16
Accumulator 1-6. 1-7
Accumulator Instructions _/-79
ACI Instruction 3-2
ADC Instruction 3-2
ADD Instruction 3-4
ADI Instruction 3-5
Addressing Modes .7-75
Addressing Registers 1-7
ANA (AND) Instruction · 3-6
AND Operator .2-73
ANI (AND Immediate) Instruction · 3-7
Arithmetic Expression Operators .2-12
Arithmetic Instructions .7-77
ASCII Constant 2-6
ASEG (Absolute Segment) Directive ,4-74
Assembler. Need for 1-3
Assembler Character Set 2-1
Assembler Compared with PL/M 1-3
Assembler Function . 1-1
Assembler Termination .4-70
Assembly-Time Expression Evaluation .2-11
Auxiliary Carry Flag ,7-77
Auxiliary Carry Flag Setting - 8080/8085 Differences ./-72

Binary Data (Coding Rules) · 2-6
blank (character) · 2-3
Branching Instructions 7-78. 7-22
Branch Table · 6-1
Byte Isolation Operations .2-74

CALL Instruction 3-8
Carry Flag . ./-/0
CC (Call if Carry) Instruction .3-70
CM (Call if Minus) Instruction .3-70
CMA (Complement Accumulator) Instruction ,3-ll
CMC (Complement Carry) Instruction ,3-72
CMP (Compare) Instruction .3-72
CNC (Call if no carry) Instruction ,3-/4
CNZ (Call if not Zero) Instruction .3-74
Combined Addressing Modes .7-/6
Comment Field · 2-4
Compare Operators .2-/3
Comparing Complemented Data 2-8
Comparisons in Expressions .2-13
Complement Used for Subtraction · 2-7
Complemented Data · 2-8
Concatenation 5-10.5-11.5-15.5-16

1-1

Condition Fla 5S 1-9
Conditional /J ssembly 4-8
CP (Call if I'ositlve) Instruction 3-75
CPE (Call if Parity Even) Instruction 3-76
CPI (Compan Immediate) Instruction 3-76
CPO (Call if Parity Odd) Instruction 3-77
CSEG (Code Segment) Directive 4-75
CZ (Call if ,~ero) Instruction . 3-78

DAA (Decim; I Adjust Accumulator) Instruction 3-78
DAD (DoublE Register Add) Instruction 3-20
Data Access Example 4-7
Data Definiti<n 4-3
Data Descrtpt on Example 4-6
Data for Subroutines 6-3
Data Label 2-5
Data Transfer Instructions 7-76
DB (Define Iiyte) Directive .4-3
DCR (DecrelT ent) Instruction 3-20
DCX (DecrelT ent Register Pair) 3-22
Decimal AddiCion Routine 6-12
Decimal Data (Coding Rules) 2-5
Decimal Subt 'action Routine 6-14
Delimiters 2-2
DI (Disable Interrupts) Instruction .3-22,3-60
Direct Addre~ sing 7-75
Divide (Soft', are Example) 6-9
Division in Expressions 2-12
DS (Define ~ torage) Directive 4-5
DSEG (Data Segment) Directive 4-75
Dummy Paralneters 5-4
DW (Define Nord) Directive 4-4

EI (Enable I:1terrupts) Instruction 3-23
ELSE Directi'e . 4-8
END Directlv ~ 4-70
ENDIF Direclve 4-8
ENDM (End Macro) Directive 5-5,5-6,5-7,5-12
EOT Directive 4-77
EPROM 1-5
EQ Operator 2-73
EQU Directlv ~ 4-2
EXITM (Exit Macro) DireClive 5-9
Expression E' aluatton 2-11
Expression O,erators 2-11
Expressions 2-6
Expressions. I'recedence of Operators 2-75
Expressions, ~ange of Values 2-75
EXTRN Dire, tive . . . 4-77

1-2

GE Operator 2-73
General Purpose Registers 7-7
GT Operator 2-73

Hardware Overview 1-5
Hexadecimal Data (Coding Rules) 2-5
HIGH Operator 2-74, 3-2, 3-5, 3-7, 404
HLT (Halt) Instruction . . . . . . 3-24

IF Directive 4-8
Immediate Addressing 7-75
Implied Addressing 7-75
IN (Input) Instruction . 7-74, 3-24
INPAGE Reserved Word ·4-74,4-75
Input/Output Ports 7-74
IN R (I ncrement) Instruction 3-25
Instruction Addressing Modes 7-75
Instruction Execution 1-9
Instruction Fetch 1-8
Instructlon Label 2-6
Instruction Naming Conventions 1-16
Instruction Set GUide 7-23
Instruction Summary .1-19,7-23
Instruction Timing 3-7
Instructions as Operands 2-7
INTE Pin 3-49
Internal Registers 1-6
Interrupt Subroutines 7-4
Interrupts 7-1
Interrupts (8085) 1-24
INX (Increment Register Pair) Instructions 3-26
IRP (Indefinite Repeat) Directive .5-8, 5-12,5-22
IRPC (Indefinite Repeat Character) .5-8,5-12,5-17

)C (J ump if Carry) Instruction 3-26
JM (J ump if Minus) Instruction 3-27
JMP (J ump) Instruction 3-28
JNC (Jump if no carry) Instruction 3-28
JNZ (J ump if not zero) Instruction 3-29
JP (Jump if Positive) Instruction 3-29
JPE (Jump if parity Even) 3-30
JPO (J ump if parity Odd) 3-37
j Z (J ump if Zero) Instruction 3-32

Label Field 2-3
Labels 2-6
LDA (Load Accumulator Direct) Instruction 3-32
LDAX (Load Accumulator Indirect) 3-33

1-3

LE OperatOl 2-13
LIB Prograrr 4-12
LHLD (Load L Direct) Instruction 3-34
LINK Progr; m 4-12,4-14,4-15
Linkage 4-16
List File 1-1
LOCAL Dip-ctive 5-5
LOCAL Syrlbols 5-6
LOCATE Pr Jgram 4-12,4-13,4-14,4-19
Location Counter (Coding Rules) 2-6
Location Counter Control (Absolute Mode) 4-77
Location Counter Control (Relocatable Mode) 4-74
Logical Instr uctions 7-17
Logical Instl uctions, Summary 3-6
Logical Ope-a tors 2-13
LOW Opera:or 2-74, 3-2, 3-5,3-7,4-4
LT Operato 2-13
LXI (Load Register Pair Immediate) 3-35

Macros 5-1
Macro Calls 5-12
Macro Defir Ition 5-4
MACRO Dir ective 5-4
Macro Expa lSlon 5-15
Macro Parar leters 5-5
Macros verslls Subroutines 5-3
Manual ProFamming 1-3
Memory 1-5
Memory Management with Relocation 4-72
Memory REservation 4-5
MEMORY I:eserved Word 4-19
MOD Opera tor 2-12
Modular Pr<gramming 4-72
MODULE [efault Name 4-17
MOV (MovE) Instruction 3-36
Multibyte P ddition Routines 6-11
Multibyte S Jbtraction Routine 6-11
Multiplicatiol in Expressions 2-12
Multiply (Software Example) 6-7
MVI (Move Immediate) 3-37

NAME Dire;tive 4-78
NE Operatcr 2-13
Nested Maco Calls 5-14
Nested Mac'o Definitions 5-12
Nested Sub-outines 3-48
Nine's Com~lement 2-7
NOP (No Operation) Instruction 3-38

1-4

NOP via MOV . , , 3-36
NOT Operator . , 2-73
NUL Operator ,2-13.5-77
Null Macros 5-16
Null Parameter 5-11

Object Code 7-2
Object File 1-1
Octal Data (Coding Rules) 2-5
One's Complement 2-7
Opcode 1-1
Opcode Field 2-4
Operand Field 2-4
Operand Field (Coding Rules) 2-4
Operands 2-5
Operators, Expression 2-11
OR Operator 2-73
ORG (Origin) Directive (Absolute Mode) 4-77
ORG (Origin) Directive (Relocatable Mode) 4-76
ORA (Inclusive OR) Instruction 3-38
OR! (Inclusive OR Immediate) 3-40
OUT Instruction 1-14.3-47

PAGE Reserved Word . 4 c74, 4-75
Parity Flag 7-77
PCHL (Move H & L to Program Counter) Instruction 3-42
Permanent Symbols 2-11
PL/M 1-3
PL/M Compared with Assembler 1-3
POP Instruction 3-42
POP PSW instruction 3-43
Precedence of Expression Operators 2-75
Processor Registers 1-9
Program Counter 1-6
Program linkage Directives 4-76
Program listing 1-2
Program Status 1-13
Program Status Word (PSW) 7-74
Programming the 8085 1-24
PROM 1-5
PSW .7-74, 3-45
PUBLIC Directive 4-77
PUSH Instruction 3-44
PUSH PSW Instruction 3-45

RAM 1-5
RAM versus ROM 4-6
RAL (Rotate Left through Carry) Instruction 3-45

1-5

RAR (Rotte Right through Carry) Instruction 3-46
RC (Retum if Carry) Instruction 3-47
Redefinable Symbols 2-11
Register AddreSSing 7-75
Register Injirect Addressing 7-76
Register Pc ir Instructions 7-27
Register Pc irs 1-7
Relocatabili ty Defined 4-72
Relocatable Expressions .2-76,2-79
Relocatable Symbols 2-11
Relocation Feature 1-2
Reserved 5ymbols 2-9
RESET Si f nal 3-24
RET (Retl rn) Instruction 3-48
REPT DirE ctive 5-6,5-12,5-15,5-16,5-17,5-18
RIM (Read Interrupt Mask) 8085 Instruction 3-48
RLC (Rot, te Accumulator Left) Instruction 3-49
RM (RetUi n if Minus) Instruction 3-50
RNC (Retllrn if no Carry) Instruction 3-57
RNZ (Retllrn if not Zero) Instruction 3-57
ROM 1-5
RP (Retur 1 if Positive) Instruction 3-52
RPE (Retun if Parity Even) Instruction 3-52
RPO (RetiTn if Parity Odd) Instruction 3-53
RRC (Rot Ite Accumulator Right) Instruction 3-53
RST (Restlrt) Instruction 3-54
RST5.5 . 3-49, 3-55, 3-59, 3-60
RST6.5 . 3-49, 3-55, 3-59, 3-60
RST7.5 3-49, 3-55, 3-59, 3-60
RZ (Return if Zero) Instruction 3-55

Savings Program Status 7-73
SBB (Subtract with Borrow) Instruction 3-56
SBI (Subtlact Immediate with Borrow) Instruction 3-57
Scope of Symbols 2-10
SET Direc:ive 4-3
Shift Expression Operators 2-12
Shift Opel ations in Expressions 2-12
SHL Oper.ltor 2-72
SHLD (St"re H & L Direct) Instruction 3-58
SHR Operltor 2-72
Sign Flag 7-70
SIM (Set Interrupt Mask) 8085 Instruction 3-59
Software Divide Routine 6-7
Software I~ultiply Routine 6-7
Source Coje Format 2-1
Source Lilie Fields 2-1
Source Program File 1-1
SPHL (Mcve H & L to Stack Pointer) Instruction 3-67

1-6

SP (Stack Pointer Register) 3-35
STA (Store Accumulator Direct) Instruction 3-67
Stack 7-7 2
Stack and Machine Control Instructions 1-19
Stack Operations 1-13
Stack Pointer 1-72
STACK Reserved Word 4-79, 3-35
Start Execution Address 4-10
STAX (Store Accumulator Indirect) Instruction 3-62
STC (Set Carry) Instruction 3-63
STKLN Directive 4-18
SUB (Subtract) Instruction 3-63
Subroutine Data 6-3
Subroutines , 1;72, 3-9
Subroutines versus Macros 5-3
Subtraction for Comparison 3-12
SUI (Subtract Immediate) Instruction 3-64
Symbol-Cross-Reference File 1-1,1-3
Symbol Definition 4-2
Symbol Table 2-9
Symbol ic Addressing 2-9
Symbols 2-9
Symbols, Absolute 2-11
Symbols (Coding Rules) 2-9
Symbols, Global 2-10
Symbols, limited 2·10
Symbols, Permanent 2·11
Symbols, Redefinable 2-11
Symbols, Relocatable 2-11
Symbols, Reserved 2·9

TRAP Interrupt 3-54
Ten's Complement 2-7
Testing Relocatable Modules 4-19
Timing Effects of Addressing Modes 1·16
TRAP (8085) 3-23
Two's Complement Data 2-7

Use of Macros 5-1
Using Symbols for Data Access 4-7

Val ue of ExpreSSions 2-15

What is a Macro? 5·2
Word Instructions 7·27
Word Storage in Memory 4-4
Work Registers 1-7

.7

XCHG (Excllange H & L with D & E) Instruction 3-65
XOR Operator 2-73
XRA (Exclu ;Ive OR) Instruction 3-66
XRI (Exclus ve OR Immediate) Instruction 3-67
XTHL (Exciange H & L with Top of Stack) Instruction 3-69

Zero Flag 7-77

& (ampepand) 5-10
<> (angle brackets) 5-10
CR (carriag = return character) 2-2
(colon) 2-2
(comm.) 2-2
(doubk semicolon) 5-10
(divlslo 1) Operator 2-12
(excian ation pOint) 5-10
HT (horizo ltal tab character) 2-2
(minus) Operator 2-12
* (multiplication) Operator 2-12
( ) (parent 1eses) 2-2
+ (plus) Operator 2-12
??nnnn Svmbo s 5-5
(semic( Ion) 2-2
(single quote) 2-2
space (charac .er) 2-2

8080/8085 !)ifferences 7-24
8085 Featul es 1-24
8085 Proces ;or 7-24
8085 Programming 1-24

1-8

Intel 8080 8085 assembly language programming 1977 intel

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Intel 8080 8085 assembly language programming 1977 intel