Central Processing Unit:
The CPU consists of ALU (Arithmetic and Logic Unit), register unit and control
unit. The CPU fetches the stored instructions from the program memory, data
word from data memory or from an input device and after processing the data
stores the result in data memory or sends it to an output device.
a) ALU (Arithmetic and Logic Unit)
This unit performs computing functions these functions are arithmetic operations
such as addition, subtraction and logical operation such as AND, OR, XOR,
rotate, compare etc. Results are stored either in registers or in memory or sent to
output devices.
b) Register Unit:
It contains various 8-bit or 16-bit registers. These registers are used primarily to
store data temporarily during the execution of a program. Some of the registers
are not accessible to user but they are used by the processor for the execution of
an instruction. 8085A microprocessor contains 8-bit registers such as
Accumulator (Reg. A), B, C, D, E, H, L etc. and16-bit registers such as Program
Counter (PC), Stack Pointer (SP).
c) Control Unit:
It provides necessary timing & control signals required for the operation of
microcomputer. It controls the flow of data between the microprocessor and
peripherals (input, output & memory).
