Introduction of Microprocessor:
The first question comes in a mind "What is
a microprocessor?”.
Let us
start with a more familiar term computer. A digital computer is an electronic
machine capable of quickly performing a wide variety of tasks. They can be used
to compile, correlate, sort, merge and store data as well as perform
calculations.
A digital computer is different from a general
purpose calculator in that it is capable of operating according to the
instructions that are stored within the computer whereas a calculator must be
given instructions on a step by step basis. By the definition a programmable calculator
is a computer.
Historically, digital computers have been
categorized according to the size using the words large, medium, minicomputer
and microcomputer. In the early years of development, the emphasis was on large
and more powerful computers. Large and medium sized computers were designed to
store complex scientific and engineering problems. These computers were
accessible and affordable only to large corporations, big universities and
government agencies. In late 1960s, minicomputers were available for use in a
office, small collage, medium size business organization, small factory etc. As
the technology has advanced from SSI to VLSI & SLSI (Very Large Scale Integration
& Super Large Scale Integration) the face of the computer has changed. It
has now become possible to build the control processing unit (CPU) with its
related timing functions on a single chip known as microprocessor. A
microprocessor combined with memory and input/output devices forms a
microcomputer. As for as the computing power is concerned the 32- bit microcomputers
are as powerful as traditional mainframe computers. The microcomputer is making
an impact on every activity of mankind. It is being used in almost all control
applications. For example analytical and scientific instruments, data
communication, character recognition, musical instruments, household items, defense equipments, medical equipments etc.
Computers communicate and operate in binary
numbers 0 and 1 also known as bits. It is the abbreviation for the term binary digit. The bit size of a microprocessor
refers to the number of bit which can be processed simultaneously by the
arithmetic circuit of the microprocessor. A number of bits taken as a group are
this manner is called word. For example, the first commercial microprocessor
the Intel 4004 which was introduced in 1971 is a 4-bit machine and is said to
process a 4-bit word. A 4-bit word is commonly known as nibble and an 8-bit
word is commonly known as byte. Intel 8085 is an 8-bit microprocessor. It
should be noted that a processor can perform calculations involving more than
its bit size but takes more time to complete the operation. The short word
length requires few circuitry and interconnection in the CPU.
Microcomputers:
In a very general
a microcomputer is best regard as a system incorporating a CPU and assisted
hardware whose purpose is to manipulate data in same fashion. This is exactly
what any digital circuit designed using SSI’s and MSI’s will also do therefore,
microcomputer should be regard as a general purpose logic device. In contrast
to standard SSI’s and MSI’s where the manufacturer decides what the device will
do, with microcomputer it is the user who decides what the device should do by
asking it to execute a proper set of instructions. A microcomputer, from this
point of view is merely an assembly of devices whose sole task is to ensure
that the instruction desire are indeed carried out properly and to allow the microprocessor
to communicate with the real world, i.e. the user environment. The power of the
microcomputer lies in the fact that if the application change, the same system
can still used by appropriately modifying the instruction to be executed and if
necessary some changes in the hardware. In contrast, a digit circuit designed
using SSI’s and MSI’s for same application will need to be completely
redesigned if the application changes significantly. The objective of a
microcomputer is to manipulate data in a certain fashion specified by the
system designer. A typical microcomputer achieves their objective by getting
its CPU (microprocessor) to execute a number of instructions in the proper
sequence. This sequence of instruction comprises the program that is executed
by the micro computer.
Microcontrollers:
A microprocessor
does not have enough memory for program and data storage, neither does it has
any input and output devices. Thus when a microprocessor is used to design a
system, several other chips are also used to make up a complete system. For
many applications, these extra chips imply additional cost and increased size
of the product. For example, when used inside a toy, a designer would like to
minimize the size and cost of the electronic equipment inside the toy. Therefore,
in such applications a microcontroller is used more often than a
microprocessor. A microcontroller is a chip consisting of a microprocessor, memory
and an input/output device. There are 4 bit as well as 32 bit microcontrollers.
Evolution of the Microprocessors:
4-bit Microprocessors:
The
first microprocessor was introduced in 1971 by Intel Corp. It was named Intel
4004 as it was a 4 bit processor. It was a processor on a single chip. It could
perform simple arithmetic and logic operations such as addition, subtraction, Boolean AND and Boolean OR. It had a control unit capable of performing control
functions like fetching an instruction from memory, decoding it, and generating
control pulses to execute it. It was able to operate on 4 bits of data at a
time.This first microprocessor was quite a success in industry. Soon other
microprocessors were also introduced. Intel introduced the enhanced version of
4004, the 4040. Some other 4 bit processors are International’s PPS4 and
Thoshiba’s T3472.
8-bit
Microprocessors:
The
first 8 bit microprocessor which could perform arithmetic and logic operations
on 8 bit words was introduced in 1973 again by Intel. This was Intel 8008 and
was later followed by an improved version, Intel 8088. Some other 8 bit
processors are Zilog-80 and Motorola M6800.
16-bit Microprocessors:
The
8-bit processors were followed by 16 bit processors. They are Intel 8086 and
80286.
32-bit Microprocessors:
The
32 bit microprocessors were introduced by several companies but the most
popular one is Intel 80386.
Pentium Series:
Instead
of 80586, Intel came out with a new processor namely Pentium processor. Its
performance is closer to RISC performance. Pentium was followed by Pentium Pro
CPU. Pentium Pro allows allow multiple CPUs in a single system in order to achieve multiprocessing. The MMX extension was added to Pentium Pro and the
result was Pentium II. The low cost version of Pentium II is celeron.
The
Pentium III provided high performance floating point operations for certain
types of computations by using the SIMD extensions to the instruction set.
These new instructions makes the Pentium III faster than high-end RISC CPUs.
Interestingly
Pentium IV could not execute code faster than the Pentium III when running at
the same clock frequency. So Pentium IV had to speed up by executing at a much
higher clock frequency.
Microcomputer Organization:
The
basic components of a microcomputer are:
- CPU
- Program memory
- Data memory
- Output ports
- Input ports
- Clock generator
CPU(Central
Processing Unit):
The CPU consists of ALU (Arithmetic and Logic Unit), Register unit and Control
unit. The CPU retrieves stored instructions and data word from memory;
it also deposits processed data in memory.
ALU(Arithmetic and Logic Unit):
Arithmetic and Logic Unit performs
computing functions on data. These functions are arithmetic operations such as
additions, subtraction and logical operation such as AND, OR, Rotate etc.
Result are stored either in registers or in memory or sent to output devices.
Register Unit:
Register Unit contains various
register. The registers are used primarily to store data temporarily during the
execution of a program. Some of the registers are accessible to the uses through
instructions.
Control Unit:
Control Unit provides
necessary timing & control signals necessary to all the operations in the
microcomputer. It controls the flow of data between the microprocessor and
peripherals (input, output & memory). The control unit gets a clock which
determines the speed of the microprocessor.
The CPU has three basic functions:
- It fetches an
instructions word stored in memory.
- It determines
what the instruction is telling it to do.(decodes the instruction)
- It executes the
instruction. Executing the instruction may include same of the following major
tasks.
Program Memory:
The basic task of
a microcomputer system is to ensure that its CPU executes the desired
instruction sequence in the program properly. The instruction sequence is
stared in the program memory on initialization- usually a power up and manual
reset the processor starts by executing the instruction in a predetermined
location in program memory. The first instruction of the program should therefore
be in this location in typical microprocessor basic system, the program to be
executed is fixed one which does not change. Therefore microprocessor program
are store on ROM, or PROM, EPROM, EEPROM.
Data
Memory:
A microcomputer manipulates data according to the algorithm given
by the instruction in the program in the program memory. These instruction may
require intermediate results to be stored, the functional block in microcontroller
have same internal register which can also be used if available for such
storage external data memory is needed if the storage requirements is more. Apart
from intermediate storage, the data memory may also be used to provide data
needed by the program, to store some of the results of the program. Data memory
is used for all storage purposes other than storage of program. Therefore, they
must have head write capability RWM or RAM. It stores both the instructions to
be executed (i.e. program) and the data involved. It usually contains ROM (Read
memory). The ROM can only read and cannot be written into and is non volatile
that is, it retains its contents when the power is turned off. A ROM is
typically used to store instructions and data that do not change. For example, it
stores the monitor program if a microcomputer. One can either read from or
write into a RWM. The RWM is volatile, that is it does not retain its contents
when the power is turned off. It is used to store user programmes & data
which are temporary might change during the course of executing a program. Both
ROM & RWM are RAM (Random access memory). RWM is respectively. During a
memory read operation, the content of the addressed location is not destroyed.
During a unit operation, the original content of the addressed location is
destroyed.
Input/Output Ports:
The input & output ports provide the microcomputer the capability
to communicate with the outside world. The input ports allow data to pass from
the outside world to the microcomputer, data which will be used in the data
manipulation being done by the microcomputer, to send data to output devices. The
user can enter instruction (i.e. program) and data in memory through input
devices such as keyboard, or simple switches, CRT, disk devices, tape or card
readers. Computers are also used to measure and control physical quantities
like temperature, pressure, speed etc. For these purposes, transducers are used
to convent physical quantities into proportional electrical signals A/D computers
are used to convert electrical signals into digital signals which are sent to
the compute. The computer sends the results of the computation to the output
devices e.g. LED, CRT, D/A converters, printers etc.. These I/O devices allow
the computer to communicate with the outside world I/O devices are called
peripherals.
Clock Generation:
Operations inside the microprocessor as well as in other parts of
the microcontroller, are usually synchronous by nature. The clock generator
generates the appropriate clock periods during which instruction executions are
carried out by the microprocessor. This condition ensures that events in
different path of the systems can proceed in a systematic fashion. Some of the
microprocessors have an internal clock generator circuit to generate a clock
signal. These microprocessors require an external crystal or RC network to be
connected at the appropriate pins for deciding the operating frequency (e.g.
8085). Some microprocessors require an external clock generator (e.g. 8086). These
microprocessors also provides an output clock signal which can be used by other
devices in the microcomputer system for their can timing and synchronizing.
