Computer Architecture of 8085 Microprocessor

Computer Architecture of 8085 Microprocessor

Written by Abin     August 21, 2012   



 



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A microprocessor is an electronic device that reads instructions from memory, accepts binary data and provides output after processing data according to the instructions. You can say its function is just like human brain.Basically microprocessor consists of three important units: input unit, output unit and a memory unit.     8085 is a 8-bit microprocessor. Here the data is usually 8 bit and the address is 16 bit. Let’s analyze the each and every components of 8085 microprocessor. 

1) Register section
2) ALU
3) The buses
4) Timing & Control unit

1) Register section:
It consists of number of registers for storing data and addresses. It can be of two types:
a) General purpose registers
b) Special purpose registers

General purpose registers are used for temporary storage of data or address during execution. They are B, C, D, E, H and L. They are all 8 bit registers. So, to store 16 bit data we have to form a register pair like: BC, DE or HL.

Special purpose registers:

The following registers come under this category and each performing a special function.
Accumulator (A) – It is a 8 bit register which is used for storing the operands/data during execution.

Program counter (PC) – It is a 16 bit register used to store the memory address of the next instruction to be executed.

Index register – This is used for addressing index addressing mode.

Status register – It stores the present status of the microprocessor after any arithmetic and logical operation. It records any occurrence of carry, auxiliary carry, sign, zero and odd/even parity.

Stack pointer – It is a 16 bit register used to initialize the stack.

Instruction register – It is a 8 bit register that stores the instruction fetched from memory

2) Arithmetic and Logical Unit (ALU):It performs arithmetic and logical operations. Addition, subtraction, multiplication, division, AND, OR, XOR, NOT, shift and rotate operations are done by ALU.

3) The Buses:
It is the interface section for communication between processor and external devices. There are 3 buses

a)    Address bus – It carries the address of the instruction. It is 16 bit wide and unidirectional.
b)    Data bus – It carries data between external devices and processor. It is 8 bit wide and bidirectional.
c)    Control bus – It is used to send control signals to different units of microprocessor.

4) Timing & Control unit:
It generates the clock signals and control signals for communication between processor and peripheral devices.