Description of 8085 pins


The 8085 is an 8-bit microprocessor designed by Intel in 1977 using NMOS technology that can address 64K Byte of memory. It has 40 pins DIP (Dual Inline Package) IC.

In bellow fig, the pin number, and its associated functions are indicated for each of the 40 pins:

Data pins

AD7-0 are known as data pins and carries lower order address bits of memory and  I/O Address. These pins are bi-directional pins. The same lines are used for both receiving information and sending out information because, at any instant of time, the processor is either receiving or sending out information, but not both.

Address pins

A15-8 carries higher order address bits and they are unidirectional.

Control pins

RD `and WR` are control pins – RD` stands for “Read*”. RD`is an active low output signal and WR`stands for “Write*”. WR` is also an active low output signal. 

Status pins

ALE – ALE(Address Enable Latch) is the control signal which is nothing but a positive going pulse generated when a new operation is started by the microprocessor.

IO/M’ –It is used to select I/O or Memory operation.

S1, S0 – They denote the status of data on the data bus

Clock pins

X1, X2 –Acrystal is connected to these pins and they are input clock signals.

CLK OUT –Thisis used as the output system clock for devices connected with the microprocessor.

Interrupt pins

There are several interrupt pins in 8085 microprocessor. They are -

TRAP, RST 7.5, RST 6.5, RST 5.5,INTR, INTA.

Theseinterruptsaregenerated by external devices to request the microprocessor to perform a task.

DMA(Direct Memory Access) pins

HOLD,HLDA– These pins are used when data transfer is to be performed directly between an external device and the main memory of the system.

Reset Pins

Reset In is used to reset 8085 whereas Reset Out can be used to reset other devices in the system.

Serial I/O pin

SOD (serial output Data line), SID (SerialInput Data line) are used for serial communication in microprocessor.

Power Supply pins

Vss pin, which should be connected to ground and Vcc pin, which should be connected to +5 V dc supply.

Fig: Pin diagram of 8085

The following figure depicts the architecture of 8085 microprocessor – 

Published on 03-Jan-2019 12:16:28