Microprocessor.pptx

DATA TRANSFER INSTRUCTIONS
 PUSH Operand:
 It pushes the operand into top of stack.
 E.g.: PUSH BX
 POP Des:
 It pops the operand from top of stack to Des.
 Des can be a general purpose register, segment register (except CS) or memory
location.
 E.g.: POP AX

Data Transfer Instructions
IN Accumulator, Port Address:
• It transfers the operand from specified port to accumulator register.
• E.g.: IN AX, 0028 H
OUT Port Address, Accumulator:
• It transfers the operand from accumulator to specified port.
• E.g.: OUT 0028 H, AX

LEA Register, Src [Load Effective Address]
• It loads a 16-bit register with the offset address of the data specified by the
Src.
E.g.: LEA BX, [DI]
• This instruction loads the contents of DI (offset) into the BX register.

LES Des, Src [load ES register]
• It loads 32-bit pointer from memory source to destination register and ES.
• The offset is placed in the destination register and the segment is placed in ES.
• This instruction is very similar to LDS except that it initializes ES instead of DS.
• E.g.: LES BX, [0301 H]

LAHF:
It copies the lower byte of flag register to AH.
SAHF:
It copies the contents of AH to lower byte of flag register.
PUSHF:
Pushes flag register to top of stack.
POPF:
Pops the stack top to flag register.

Arithmetic Instructions
MUL Src:
• It is an unsigned multiplication instruction.
• It multiplies two bytes to produce a word or two words to produce a double word.
AX = AL * Src
DX : AX = AX * Src
• This instruction assumes one of the operand in AL or AX.
• Src can be a register or memory location.
IMUL Src:
• It is a signed multiplication instruction.

8 bit multiplication
 AL is multiplicand.
 AX keeps the result
 MOV AL,10h ; AL = 10h
 MOV CL,13h ; CL = 13h
 IMUL CL ; AX = 0130h

• AX is multiplicand
• DX:AX keep the result
• MOV AX,0100h ; AX = 0100h
• MOV BX,1234h ; BX = 1234h
• IMUL BX ; DX = 0012h
; AX = 3400h
16 bit multiplication

DIV Src:
• It is an unsigned division instruction.
• It divides word by byte or double word by word.
• The operand is stored in AX, divisor is Src and the result is stored as:
• AH = remainder AL = quotient
IDIV Src:
• It is a signed division instruction.

 AL is dividend
 AL keep the result
 AH keep the remainder
 MOV AX, 0017h
 MOV BX, 0010h
 DIV BL ; AX = 0701
8 bit division

16 bit division
 DX:AX dividend.
 AX keep the result, DX keep the remainder.
 MOV AX,4022h ;
 MOV DX,0000h ;
 MOV CX,1000h ;
 DIV CX ;AX = 0004
;DX = 0022

CBW (Convert Byte to Word):
• This instruction converts byte in AL to word in AX.
• The conversion is done by extending the sign bit of AL throughout AH.
CWD (Convert Word to Double Word):
• This instruction converts word in AX to double word in DX : AX.
• The conversion is done by extending the sign bit of AX throughout DX.

 MOV AL,22h
 CBW ; AX=0022h
 MOV AL,90h
 CBW ; AX=FF90h
 MOV AX, 3422h
 CWD ; DX=0000h
; AX=3422h
Ex. Conversion

BIT MANIPULATION INSTRUCTIONS
• These instructions are used at the bit level.
• These instructions can be used for:
Testing a zero bit
Set or reset a bit
Shift bits across registers

BIT MANIPULATION INSTRUCTIONS
XOR Des, Src:
• It performs XOR operation of Des and Src.
• Src can be immediate number, register or memory location.
• Des can be register or memory location.
• Both operands cannot be memory locations at the same time.
• CF and OF become zero after the operation.
• PF, SF and ZF are updated.

Bit Manipulation Instructions
SHL Des, Count:
• It shiftS bits of byte or word left, by count.
• It puts zero(s) in LSBs.
• MSB is shifted into carry flag.
• If the number of bits desired to be shifted is 1, then the immediate
number 1 can be written in Count.
• However, if the number of bits to be shifted is more than 1, then the
count is put in CL register.

SHR Des, Count
• It shift bits of byte or word right, by count.
• It puts zero(s) in MSBs.
• LSB is shifted into carry flag.

SAL Des, Count:
• It shiftS bits of byte or word left, by count.
• It puts zero(s) in LSBs.
• MSB is shifted into carry flag.
• If the number of bits desired to be shifted is 1, then the immediate number 1 can be
written in Count.
• However, if the number of bits to be shifted is more than 1, then the count is put in CL
register.

SAR Des, Count
•It shift bits of byte or word right, by count.
•It does not change MSB, rather MSB is copied to the next bit and retains its value.
•LSB is shifted into carry flag.
•If the number of bits desired to be shifted is 1, then the immediate number 1 can be written in
Count.
•However, if the number of bits to be shifted is more than 1, then the count is put in CL register.

ROL Des, Count
• It rotates bits of byte or word left, by count.
• MSB is transferred to LSB and also to CF.
• If the number of bits desired to be shifted is 1, then the immediate number 1 can be
written in Count.
• However, if the number of bits to be shifted is more than 1, then the count is put in
CL register.

ROR Des, Count:
• It rotates bits of byte or word right, by count.
• LSB is transferred to MSB and also to CF.

• RCR Des, Count
• Used to rotate bits of byte/word towards the right, i.e. LSB to CF and CF to MSB.
• RCL Des, Count
• Used to rotate bits of byte/word towards the left, i.e. MSB to CF and CF to LSB.

PROGRAM EXECUTION TRANSFER INSTRUCTIONS
• These instructions cause change in the sequence of the execution of instruction.
• This change can be through a condition or sometimes unconditional.
• The conditions are represented by flags.

• CALL Des:
• This instruction is used to call a subroutine or function or procedure.
• The address of next instruction after CALL is saved onto stack.
• RET:
• It returns the control from procedure to calling program.
• Every CALL instruction should have a RET.

JMP Des:
This instruction is used for unconditional jump from one place to another.
Jxx Des (Conditional Jump):
All the conditional jumps follow some conditional statements or any instruction that
affects the flag.

Mnemonic Meaning Jump Condition
JA Jump if Above CF = 0 and ZF = 0
JAE Jump if Above or Equal CF = 0
JB Jump if Below CF = 1
JBE Jump if Below or Equal CF = 1 or ZF = 1
JC Jump if Carry CF = 1
JE Jump if Equal ZF = 1
JNC Jump if Not Carry CF = 0
JNE Jump if Not Equal ZF = 0
JNZ Jump if Not Zero ZF = 0
JPE Jump if Parity Even PF = 1
JPO Jump if Parity Odd PF = 0
JZ Jump if Zero ZF = 1

Loop Des:
• This is a looping instruction.
• The number of times looping is required is placed in the CX register.
• With each iteration, the contents of CX are decremented.
• ZF is checked whether to loop again or not.

String Instructions
• String in assembly language is just a sequentially stored bytes or words.
• There are very strong set of string instructions in 8086.
• By using these string instructions, the size of the program is considerably reduced.

• CMPS Des, Src
• It compares the string bytes or words.
• SCAS String
• It scans a string.
• It compares the String with byte in AL or with word in AX.
String Instructions

• MOVS / MOVSB / MOVSW:
• It causes moving of byte or word from one string to another.
• In this instruction, the source string is in Data Segment and destination string is in Extra
Segment.
• SI and DI store the offset values for source and destination index.
String Instructions

• REP (Repeat):
• This is an instruction prefix.
• It causes the repetition of the instruction until CX becomes zero.
• E.g.: REP MOVSB STR1, STR2
• It copies byte by byte contents.
• REP repeats the operation MOVSB until CX becomes zero.
String Instructions

Processor Control instruction
• STC:
• It sets the carry flag to 1.
• CLC:
• It clears the carry flag to 0.
• CMC:
• It complements the carry flag.

• STD:
• It sets the direction flag to 1.
• If it is set, string bytes are accessed from higher memory address to lower memory address.
• CLD:
• It clears the direction flag to 0.
• If it is reset, the string bytes are accessed from lower memory address to higher memory address.
Processor Control instruction

These instructions are used to execute the given instructions for a number of times.
Following is the list of instructions under this group −
•LOOP − Used to loop a group of instructions until the condition satisfies, i.e., CX = 0
•LOOPE/LOOPZ − Used to loop a group of instructions till it satisfies ZF = 1 & CX = 0
•LOOPNE/LOOPNZ − Used to loop a group of instructions till it satisfies ZF = 0 & CX = 0
•JCXZ − Used to jump to the provided address if CX = 0
Iteration Control Instructions

These instructions are used to call the interrupt during program execution.
INT
• Used to interrupt the program during execution and calling service specified.
INTO
• Used to interrupt the program during execution if OF = 1.
IRET
•Used to return from interrupt service to the main program.
Interrupt Instructions

Microprocessor.pptx

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