Microprocessor 8085 Pinout Diagram and Pin Description


8085 is the 8 bit microprocessor designed by Intel in 1977. It is a Dual Inline Package(DIP) integrated circuit built with NMOS technology. Here, you can see the pin diagram of 8085 microprocessor.

Microprocessor 8085 Pinout Diagram, pin diagram of 8085


Pin no 1 and 2


Pin 1 and 2 are named as X1 and X2. These pins are used to connect an external crystal oscillator. It provides the pulse signal to the internal clock generator. The frequency of the internal clock generator is divided by 2.


Pin No 3


Pin no 3 is the RESET Out. It is used to make reset all the external devices connected to the microprocessor. When the microprocessor is reset, all the external devices also be reset. 


Pin No 4


Pin no 4 is SOD or Serial Output Data Line. It is used for serial data connection and helps to transfer data from microprocessor to external device.


Pin No 5


Pin no 5 is SID or Serial Input Data Line. It is also used for serial data communication and helps to transmit data from the external device to the microprocessor.


Pin No 6 to 10


These five pins are used for the external interrupt signal to terminate the current program. The microprocessor has a total of five interrupts,
  1. TRAP
  2. RST 7.5
  3. RST 6.5
  4. RST 5.5
  5. INTR

Pin No 11


It is INTA or Interrupt Acknowledge. It helps to tell the external interrupt hardware that the microprocessor acknowledge the interrupt and started the program executing.


Pin No 12 to 19


Pin no 12 to 19 are the bidirectional pins and these are used to carry both address and data bits. Generally, they are used to carry 8-bit data.


Pin No 20


Pin no 20 is the Vss or Ground. It is used to connect the negative pin of the power supply.


Pin No 21 to 28


These are the unidirectional pins used to carry the bits of the address of the memory at which the data is stored.


Pin No 29, 33, and 34


Pin no 29 and 33 are the S0, S1, and IO/M'. These are used for the status signal. They help to show the current programming status of the microprocessor such as Halt, memory read-write, I/O read-write, opcode fetch, interrupt acknowledge, etc.


Pin no 30


Pin no 30 is the ALE or Address Latch Enable. When the pulse signal in this pin is high then it indicates the address or fetching of the address from the memory but when the pulse signal in this pin is low then it indicates the data or receiving of data from the memory.


Pin No 31 and 32


These are the WR' or Write and Read or RD' pins. Both of these are the active low pins. The WR' pin is used to store the data from the microprocessor to external memory whereas thr RD' pin is used to fetch data from the external memory to the microprocessor.


Pin No 35


READY - It is the pin through which the external hardware tells or sends the message that they are ready to communicate with the microprocessor.

Pin No 36


RESET IN - It is used to reset the microprocessor by the external hardware or signal.

Pin No 37


CLK OUT - The Clock Out pin is used to carry the clock pulse signal from the microprocessor to the externally connected hardware that helps for the synchronization between the microprocessor and external hardware.


Pin No 38 and 39


Pin 38 or HLDA helps to communicate that the microprocessor is accepted the hold signal and holds its current data transfer. On the other hand pin, 39 or HOLD is used to communicate that the external device sends the signal to the microprocessor to hold the current data transfer.


Pin No 40


It is the Vcc pin and is used to connect the positive pin of the power source.


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Microprocessor 8085 Pinout Diagram and Pin Description Microprocessor 8085 Pinout Diagram and Pin Description Reviewed by Author on 11/22/2021 Rating: 5
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