8085 Microprocessor

4 Pin Diagram of 8085

                                     Fig: pin diagram of 8085

8085 up is an 8-bit general purpose microprocessor capable of addressing 64Kb of memory.

The device has 40 pins,+5 V power supply, operate on 3 to 5 MHZ frequency single phase clock.

All the signals can be classified in 8085 up pin diagram into six groups –

1)  Address Bus:  in this 16 signals lines. These lines are splits into two segments -

a) A15-A8 – unidirectional and used for the higher order address (MSB).

b)AD7-AD0 – Dual purpose such as data bus as well as lower address data bus(LSB).


2)  Control and status signals: these signals are used to identify the nature of operation.

 Three control signals that are-

RD – it is a active low signal. Which indicate that the selected IO or Memory device is to be read and data is available on the data bus.

WR-it is a active low signal which indicate that the data on the data bus are to be written into a selected memory or IO location.

ALE- it is a +ve going pulse generated everytime the 8085 begins an operation (machine cycle): which indicate that the bits on AD7-AD0 are address bits.

Three status signals that are

IO/M- this is a status signal used to differentiate between IO and Memory operations.when it is hign then IO operation and When it is low then Memory operation.

S1 and S0- status signals,similar to IO/M,can identify various operations.that are rarely used in the systems.