INTRODUCTION TO MICRO-COMPUTERS AND MICRO-PROCESSORS
A computer system has three main components: a Central Processing Unit (CPU) or processor, a
Memory Unit and Input Output Units (devices). Below is a block diagram for a microcomputer:
Memory
The memory status usually consists of a mixture of RAM & ROM. It also can have magnetic
hard disks or optical disks. The memory can store the binary codes and also the binary coded
data with which the computer is going to be working.
Input/Output
The I/O section allows the computer to take in data from the outside world or send the data to the
outside world. The peripherals such as keyboards, video display terminals, printers and modems
are connected to I/O section. These allow the user and the computer to communicate with each
other. The actual physical devices used to interface the computer buses to external systems are
often called ports. The input port allows data from a keyboard, an A/D converter or some other
source to be read in to the computer under the control of CPU. An O/P Port is used to send data
from display terminal, a printer, or a D/A converter .
Central Processing Unit
The central processing unit or CPU controls the operation of the computer. THE CPU fetches
binary coded instructions from memory, decades the instructions into a series of simple actions
and carries out these actions in a sequence of steps. The CPU also contains an address counter or
instruction pointer register which holds the address of the next instruction, or data item to be
fetched from binary data and circuitry which generates the control bus signals.
•Address Bus- The address bus consists of 16,20,24,32 parallel signal lines. On these
lines the CPU sends out the address of the memory location. If the CPU has N address
lines then it can directly address 2N memory locations.
•Data Bus- The data bus consists of 8, 16, or 32 parallel signal lines. The double ended
arrows on the data bus means that the CPU can read data in from memory or from a port
on these lines, or it can send data out to memory or to a port on these lines.
•Control Bus- The control bus consists of 4 to 10 parallel signal lines. The CPU sends
out signals on the control bus to enable the outputs of addressed memory devices or port
devices. Typical control bus signals are memory read, memory write, I/O read, and I/O
write. To read a byte of data from a memory location, the CPU sends out the memory
address of the desired byte on the address bus and then sends out the memory read
signal on the control bus. The memory read signal enables the address memory device
to output a data word on to the data bus. The data word from the memory travels along
the data bus to the CPU.
Microprocessor
In any microcomputer system, the component which actually processes data is entirely contained
on a single chip called Microprocessor (MPU). A microprocessor is a single chip integrating all
the functions of a central processing unit (CPU) of a computer. In some cases, the terms 'CPU'
and 'microprocessor' are used interchangeably to denote the same device.
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