8085 Microprocessor - Reader's Bird View

In today's fast-paced environment, every thing requires to be clock-driven, from laser printer to semi-automatic washing machine to car stereo to digital timepiece to apple iPhone. Microprocessors are able to perform substantial (similar or non similar) work per clock cycle. The clock speed determines how many instructions per second the microprocessor/CPU can execute.

If required to define, a microprocessor is a digital electronic component with miniaturized transistor (N-MOSFET ) components on a single semiconductor integrated circuit.


Lets start with a basic microprocessor, the beginners in the INTEL series in the late 1970's: 8085


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An 8-bit processor

16-bit address bus

Program, data and stack memories occupy the same memory space.

Total addressable memory size is 64 KB = 65536 bytes =  2 pow 32

Stack grows downward

Jump, branch and call instructions use 16 bit addresses

5 interrupts with unequal priority

256 input ports

256 output ports

16 bit program counter

Stack pointer is a 16 bit register, always incremented/decremented by 2

Logical instruction set -AND, OR, XOR, ROTATE

Arithmetic instruction set - Add, Subtract, Increment, Decrement

It has single 5 volt power supply

Processor speed - 3 MHz

Multiplexed address and data bus

Manufactured with N-MOS technology