Microprocessor

Unit – I: Introduction to Microprocessor
Introduction to Microprocessor and its application
Microprocessor Evaluation Tree
Microprocessor Architecture (Harvard & Princeton)
General Architecture of the Microprocessor and its
operation
Component of Microprocessor System: Processor,
Buses, Memory, Input-Outputs(I/O’s) and other
interfacing devices

What is Microprocessor
Microprocessor is a computer Central Processing Unit (CPU)
onasinglechip.
Itcontainsmillionsof transistors connectedbywires.

BUSES
The data bus is a bidirectional group of lines on
which the data can travel both ways, i.e., from a
microprocessor to a device and vice versa.
The address bus is a unidirectional group of lines
on which address of a memory location or a device is
sent by the microprocessor.
 The control bus is a group of lines on which control
signals flow from the microprocessor to the
connected devices and vice versa. Examples of
control signals are ‘memRead’, ‘memWrite’, ‘ioRead’,
‘ioWrite’, ‘reset’, etc.Computer Fundamentals and Programming in C
6

Application’s of Microprocessor
 A microprocessor makes daily life easier because of its low cost, low
power, small weight, and vast application in every field. There are several
applications of microprocessors. Some of the important applications are:
 (1) Household Devices:- The programmable thermostat allows the
control of temperature at homes. In this system, a microprocessor works
with the temperature sensor to determine and adjust the temperature
accordingly.
 High-end coffee makers, Washing machines, and radio clocks contain
microprocessor technology.
 Some other home items that contain microprocessors are: microwaves,
toasters, televisions, VCRs, DVD players, ovens, stoves, clothes washers,
stereo systems, home computers, alarm clocks, hand-held game devices,
thermostats, video game systems, bread machines, dishwashers, home
lighting systems and even some refrigerators with digital temperature
control.

 (2) Industrial Applications of Microprocessors
Some industrial items which use microprocessors technology
include: cars, boats, planes, trucks, heavy machinery, elevators,
gasoline pumps, credit-card processing units, traffic control
devices, computer servers, most high tech medical devices,
surveillance systems, security systems, and even some doors
with automatic entry.
(3) Transportation Industry
 Automobiles, trains and planes also use microprocessor
technology.
 Consumer vehicles-buses, cars, trucks -integrate
microprocessors to communicate important information
throughout the vehicle. E.g., navigation systems provide
information using microprocessors and global positioning

 (4) Computers and Electronics
 Microprocessor-drives technology is the brain of the
computer. They are used in all type of computers ranging from
microcomputers to supercomputers.
 A cell phone or mobile device executes game instructions by
way of the microprocessor.
 VCRs, televisions and gaming platforms also contain
microprocessors for executing complex instructions and
tasks.

 (5) In Medicals
 Many medical devices, like an insulin pump, are typically
controlled by a microprocessor. The microprocessors perform
various functions, such as processing data from bio-sensors,
storing measurements, and analyzing results.
 (6) Instrumentation
 Microprocessor is also very useful in the field of
instrumentation. Function generators, frequency counters,
frequency synthesizers, spectrum analyses and many other
instruments are available, when microprocessors are used as
controller.
 (7) Entertainment
 The use of microprocessor in entertainment equipment, toys
and home entertaining applications is making them more
useful and full of features.

 (8) Embedded Systems at Home
 A number of modern devices in the home are microprocessor
based i.e. camera; washing machines; calculators; hi-fi
systems; telephones; microwave ovens; burglar alarms etc.
The input are usually simple numeric keyboards, sensors,
buttons or while the output include lights, simple LCD screens
displays, motors and relays, LEDs, buzzers etc.
 (9) Office Automation and Publication
 Microprocessor based system with software packages has
changed the office environment. Microprocessors based
systems are being used for spread sheet operations, word
processing, storage etc.
 The Publication technology has revolutionized by the

 (9) Communication
 In communication the telephone industry is most important. In
this industry, microprocessors are used in digital telephone
sets, telephone exchanges and modem etc.
 The use of microprocessor in satellite communication,
television, has made teleconferencing possible.
 Railway reservation and airline reservation system also uses
microprocessor technology. WAN (Wide Area Network) and
LAN (Local Area Network) for communication of vertical
information through computer network.

Generations of Microprocessors
13

Microprocessor Architecture (Harvard
and Princeton / Von - Neumann)

Von Neumann Architecture / Princeton Architecture
A design architecture for an electronic digital computer:
a processing unit : arithmetic logic unit and processor registers
a control unit : an instruction register and program counter,
a memory: to store both data and instructions
This architecture has evolved to be any stored-program
computer in which an instruction fetch and a data operation
cannot occur at the same time because they share a
common bus. This is referred to as the Von Neumann
bottleneck and often limits the performance of the system

Harvard Architecture
A computer Architecture with physically
separate storage and signal pathways
for instructions and data. (This term
stores instructions on punched
tape and data in electro-mechanical
counters)
Today, most processors implement such
separate signal pathways for
performance reasons but actually
implement a modified Harvard
architecture, so they can support tasks
such as loading a program from disk
storage as data and then executing it.

Compare between Von Neumann architectures and Harvard architectures:
Von Neumann architecture:
the CPU can be either reading an instruction or reading/writing data
from/to the memory. Both cannot occur at the same time since the
instructions and data use the same bus system.
Harvard architecture:
the CPU can both read an instruction and perform a data memory access
at the same time, even without a cache.
Also, a Harvard architecture machine has distinct code and data address
spaces.(instruction address zero is not the same as data address zero.)
A Harvard architecture computer can thus be faster for a given circuit
complexity because instruction fetches and data access do not contend for
a single memory pathway.

Microprocessor 8085 :-
 8085 is pronounced as "eighty-eighty-five"
microprocessor. It is an 8-bit microprocessor designed
by Intel in 1977 using NMOS technology.
 It has the following configuration −
 8-bit data bus
 16-bit address bus, which can address up to 64KB
 A 16-bit program counter
 A 16-bit stack pointer
 Six 8-bit registers arranged in pairs: BC, DE, HL
 Requires +5V supply to operate at 3.2 MHZ single
phase clock
 It is used in washing machines, microwave ovens,
mobile phones, etc.

19
Memory
Memory is a
collection of
cells,
each with a
unique physical
address
The size of a cell
is normally a
power of 2,
typically a byte
today.

20
Memory
A cell is the
smallest
addressable unit
of memory – i.e.
one cell can be
read from
memory or one
cell can be
written into
memory, but
nothing smaller.

21
RAM and ROM
 RAM stands for Random Access Memory
Inherent in the idea of being able to access each location
is the ability to change the contents of each location
 ROM stands for Read Only Memory
The contents in locations in ROM cannot be changed
 RAM is volatile, ROM is not
This means that RAM does not retain its bit configuration
when the power is turned off, But ROM does

22
MEMORY UNIT
(or RAM- Random Access Memory)
Each cell has an address, starting
at 0 and increasing by 1 for each
cell.
A cell with a low address is just as
accessible as one with a high
address- hence the name RAM.
The width of the cell determines
how many bits can be read or
written in one machine operation.
MAR is Memory Address Register
MDR is Memory Data Register

23
What is a Register?
Data can be moved into and out of registers
faster than from memory.
If we could replace all of memory with
registers, we could produce a very, very fast
computer ...
But, the price would be terribly prohibitive.
 Most computers have quite a few registers
that serve different purposes.
We’ll see how the MAR and the MDR are
used.

24
How does the memory unit work?
Trace the following
operation:
Store data D in memory
location 0.
DD00 D0 D
s
D

25
How does the memory unit work?
Trace the following
operation:
1) Fetch data D from memory
location 1.
2) Obtain an instruction I from
memory
location 7.
How does the computer distinguish
between 1) and 2) above?
We need to look at the control unit later.
1
D
f
D
I

26
USING THE DECODER CIRCUIT TO SELECT
MEMORY LOCATIONS
0
1
2
3
4
5
6
7
•
•
•
15
4 x 24
decoder
1
0 1 1 1
MAR
0
0
0
0

27
The decoder circuit doesn't scale well--- i.e. as the
number of bits in the MAR increases, the number
of output lines for the decoder goes up
exponentially.
Most computers today have an MAR of 32 bits. Thus, if
the memory was laid out as we showed it, we would
need a 32 x 232 decoder!
Note 232 is 22 230 = 4 G
So most memory is not 1 dimensional, but 2-
dimensional (or even 3-dimensional if banked memory
is used).

28
2-D MEMORY
0 1 1 1
MAR
2 x 4
decoder
2 x 4
decoder
columns
rows
Note that a 4 x 16 decoder
was used for the 1-D
memory.

29
Arithmetic/Logic Unit (ALU)
Performs basic arithmetic operations such
as adding
Performs logical operations such as AND,
OR, and NOT
Most modern ALUs have a small amount
of registers where the work takes place.
For example, adding A and B, we might
find A stored in one register, B in another,
and their sum stored in, say, A, after the
adder computes the sum.

30
The ALU Uses a Multiplexer
R
AL1
AL2
ALU
circuits
multiplexer
selector lines
output
GT EQ LT
condition code register
Register R
Other registers

31
ADD X
X
D
D
ADD X
f
ALU1 & ALU2
E
E+DE
D
E+D
E+D

32
Control Unit
A Control Unit is the unit that handles the central
work of the computer.
There are two registers in the control unit
The instruction register (IR) contains the
instruction that is being executed
The program counter (PC) contains the address of
the next instruction to be executed
The ALU and the control unit together are called the
Central Processing Unit, or CPU

33
ALL A COMPUTER DOES IS ...
Repeat forever (or until you pull the plug or the
system crashes)
1) FETCH (the instruction)
2) DECODE (the instruction)
3) EXECUTE (the instruction)

34
The Fetch-Execute Cycle
Fetch the next instruction
Decode the instruction
Execution Cycle
Gets data if needed
Execute the instruction
Normally “Get data if needed” is considered part of the
“Execute the instruction”.

35
The Fetch-Execute Cycle
(3)
(a)
(b)

36
How Does the Control Unit Work?
The PC holds the
address of the next
instruction to be
executed.
Whatever is stored
at that address is
assumed to be an
instruction.
Once the
instruction is
fetched, the
PC is
incremented
.

37
Input / Output Units
An input unit is a device through which
data and programs from the outside
world are entered into the computer
Keyboard, the mouse, and scanning
devices
An output unit is a device through which
results stored in the computer memory
are made available to the outside world
Printers and video display terminals

38
THE I/O DEVICES
Pictorially, these
look the
simplest, but in
reality, they form
the most diverse
part of a
computer.
Includes:
keyboards, monitors, joysticks, mice, tablets,
lightpens, spaceballs, ....

39
I/O UNITS
Processor Memory
I/O buffer
Control-logic
I/0 device
Each device is different, but
most are interrupt driven.
This means when the I/O
device wants attention, it
sends a signal (the interrupt)
to the CPU.

Microprocessors I - Frederick University
40
Basic Concepts
 A memory device can be le. viewed as a
single column tab
 Table index (row number) refers to the
address of the memory.
 Table entries refer to the memory contents or
data.
 Each table entry is referred as a memory
location or as a word.
 Both the memory address and the memory
contents are binary numbers, expressed in
most cases in Hex format.
 The size of a memory device is specified as
the number of memory locations X width or
word size (in bits).
 For example a 1K X 8 memory device has
1024 memory locations, with a width of 8 bits.
000
001
002
003
Hex
Memory
Contents
3FC
3FD
3FE
10011001
00111000
00-0000-0000
00-0000-0001
00-0000-0010
00-0000-0011
11-1111-1100
11-1111-1101
11-1111-1110
11-1111-1111 3FF
11001001
00111011
01101000
10111001
00110100
00011000
Memory Address
Binary
1024 X 8 (or 1KX8) Memory

41
Address Lines
A memory device or memory chip must have three
types of lines or connections: Address, Data, and
Control.
Address Lines: The input lines that select a memory
location within the memory device.
Decoders are used, inside the memory chip, to select a
specific location
The number of address pins on a memory chip specifies
the number of memory locations.
If a memory chip has 13 address pins (A0..A12), then it has:
213 = 23 X 210 = 8K locations.
If a memory chip has 4K locations, then it should have N pins:
2N = 4K = 22 X 210 = 212  N=12 address pins (A0..A11)
Location 000
Location 001
Location 002
Location 003
Location 0FC
Location 0FD
Location 0FE
Location 0FF
Y00
Y01
Y02
Y03
YFC
YFD
YFE
YFF
A00
A01
An-2
An-1

42
Data Lines
Data Connections: All memory devices have a set of data output pins (for ROM devices), or
input/output pins (for RAM devices).
Most RAM chips have common bi-directional I/O connections.
Most memory devices have 1, 8 or 16 data lines.
k- address lines
(A0..Am-1)
n-bits per
word
Data Input Lines
(DI0..DIn-1)
Read (RD)
Write (WR)
2m words
Data Output Lines
(DO0..DOn-1)
(2m X n) RAM with separate I/P
and O/P Data lines
Chip Select (CS)
k- address lines
(A0..Am-1)
n-bits per
word
Read/Write (R/W)
Chip Select (CS)
2m words
Data Input/Output
Lines (D0..Dn-1)
(2m X n) RAM with common I/P
and O/P Data lines
k- address lines
(A0..Am-1)
n-bits per
word
Output Enable (OE)
Chip Select (CS)
2m words
Data Output Lines
(D0..Dn-1)
(2m X n) ROM with only O/P Data
lines

43
Control Lines
Enable Connections:
All memory devices have at least one Chip Select (CS) or Chip Enable (CE) input,
used to select or enable the memory device.
If a device is not selected or enabled then no data can be read from, or written into
it.
The CS or CE input is usually controlled by the microprocessor through the higher
address lines via an address decoding circuit.
Control Connections:
RAM chips have two control input signals that specify the type of memory operation:
the Read (RD) and the Write (WR) signals.
Some RAM chips have a common Read/ Write (R/W) signal.
ROM chips can perform only memory read operations, thus there is no need for a
Write (WR) signal.
In most real ROM devices the Read signal is called the Output Enable (OE) signal.

44
Memory Read Operations
A memory read operation is carried out in the following steps:
The processor loads on the Address bus the address of the memory location to be read (Step 1).
Some of the address lines select the memory devices that owns the memory
location to be read (Step 1a), while the rest point to the required memory location
within the memory device.
The processor activates the Read (RD) signal (Step 2).
The selected memory device loads on the data bus the content of the memory
location specified by the address bus (Step 3).
The processor reads the data from the data bus, and resets the RD signal (Step 4).
Address Bus
Clock
Chip Enable
Read (RD)
Data Bus
T1 T2 T3
Valid Address
Valid DataInvalid Data
Step 1
Step 1a
Step 2 Step 3 Step 4

45
Memory Write Operations
A memory write operation is carried out in the following steps:
The processor loads on the Address bus the address of the memory location (Step 1).
Some of the address lines select the memory devices that owns the memory
location to be written (Step 1a), while the rest point to the required memory
location within the memory device.
The processor loads on the data bus the data to be written (Step 2).
The processor activates the Write (WR) signal (Step 3).
The data at the data bus is stored in the memory location specified by the
address bus (Step 4).
Address Bus
Clock
Chip Enable
Write (WR)
Data Bus
T1 T2 T3
Valid Address
Valid Data
Step 1
Step 1a
Step 2
Step 4
Step 3

46
Types of Semiconductor Memory Devices
Read Only Memory (ROM)
 A memory device that maintains its
data permanently (or until the device is
reprogrammed).
 Non-volatile: It maintains its data even
without power supply.
 Used to store
 Programs such as the BIOS.
 Data such as look tables
 e.g. the bit pattern of the characters in a
dot matrix printer.
 A ROM device can be
1. Masked ROM (Programmed by the
manufacturer)
2. Programmable ROM (can be program-
erased-reprogrammed many times
Random Access Memory (RAM)
• A memory device that can be read and
written.
– Volatile: It looses its data when the power
supply is switched-off
– When the supply is switched-on it contains
random data
• Used to store
– User programs that are loaded from a
secondary memory (disk)
– Temporary data used by programs such as
variables and arrays.
• A RAM device can be
1. Static
2. dynamic

47
A Read Only Memory Example
Implementation of an 8X4 ROM using (a) a decoder and OR-gates and (b) a
decoder and diodes.
Address
Data
000
0011
001
0010
010
0100
011
0011
100
1010
101
0000
110
0101
111
1000
Y2
A0
Y0
Y1
Y3
3/8 DEC.
Y6
Y4
Y5
Y7
A1
A2
E
A2
A1
A0
CS
OE
D2 D1 D0D3
Y2
A0
Y0
Y1
Y3
3/8 DEC.
Y6
Y4
Y5
Y7
A1
A2
E
A2
A1
A0
CS
OE
D2 D1 D0D3
+5V

48
A Programmable Read Only Memory Example
Implementation of an 8X4 ROM using a decoder and fused links.
Y2
A0
Y0
Y1
Y3
3/8 DEC.
Y6
Y4
Y5
Y7
A1
A2
E
A2
A1
A0
CS
OE
D2 D1 D0D3
+5V

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