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Programmable Peripheral Interface (8255)

Here we see how can we use Programmable Peripheral Interface (8255) for data transfer. As we know Programmable Peripheral Interface (8255) is used to interface input and output device with microprocessor. There are various methods of data transfer from the microprocessor to output devices or vice-versa. It has already discussed in my earlier posts.

So here we come to discuss a special interface circuits known as peripheral interface circuits. Those circuits are to be used for interfacing purpose. The interfacing devices (IC 8255) may be classified into two categories. Those are general purpose peripherals and special purpose peripherals.

What are the peripheral devices?

   Now question is what are the peripheral devices? Basically the Input/output devices which are connected to microprocessors are known as peripherals. These are printers, floppy drives, CRT and Cassette recorder, Mouse, Monitor etc.

Classification of interfacing device

In above all, we see that lots of peripherals devices can be interface with microprocessor. But we may classified those interfacing devices into two categories.

  • General purpose peripherals and
  • Special purpose peripherals.

So here we see some list of spacial general purpose peripherals. Generally we used those frequently to interface peripheral devices.

  • (1) Programmable Peripheral Interface (PPI).
  • (2) Programmable Interval Timer.
  • (3) Programmable Interrupt Controller.
  • (4) Programmable DMA Controller.
  • (5) Programmable Communications Interface.

Lets see some special purpose peripherals interfacing device for  a microprocessor. Those are used  for some specific types of I/O devices.

  • (1)Programmable Keyboard and Display Interface.
  • (2)Programmable Hard Disk Controller.
  • (3)Programmable Floppy Disk Controller.

In this post we will see detail of Programmable Peripheral Interface (8255) and its application.


If we take example of microprocessor 8085, then we can see in 8085 microprocessor, it does not has any pins or port to connect any I/O devices. So how can we connect I/O devices with 8085 microprocessor? Answer is by using Programmable Peripheral Interface (8255). Programmable Peripheral Interface (PPI) IC 8255 is provide I/O ports to 8085 microprocessor to connect I/O devices.

Programmable Peripheral Interface (PPI) IC 8255

 The input/output devices are generally connect with the microprocessor through the input/output port. The input/output port is either non-programmable or programmable. A non-programmable port can either connected as input mode or output mode. If both input and output devices have to connect to the microprocessor then two separate non-programmable ports have to use. It should connected like one for input device and other for the output device.

Pin Diagram of 8255A

 The INTEL 8255A is a programmable port device. It is most versatile Programmable Peripheral Interface. It may used to connect almost any microprocessor. This IC is widely used. It can be programmed to transfer the data to the input/output devices. It is a 40 pin dual in line IC package, whose pin configuration and block diagram shown in figures.

Programmable Peripheral Interface (PPI) IC 8255

Ports on 8255A

The IC 8255 A has three 8-bit ports. From the above pin diagram we can see those ports very clearly.

  • (1)Port-A
  • (2)Port-B and
  • (3)Port-C

Port-A is a 8 bit port. We can used this port to connect digital I/O devices. Form the pin diagram we can see that pin numbers 1 to 4 and 37 to 40 used for Port-A.


Port-B is a 8 bit port. We can used this port to connect digital I/O devices. Form the pin diagram we can see that pin numbers 18 to 25 used for Port-B.


The port-C we can used as two 4-bit ports. It represent as Port CUpper and Port CLower . We can used this port to connect digital I/O devices. Form the pin diagram we can see that pin numbers 10 to 17 used for Port-C.

In conclusion, hope this discussion on Programmable Peripheral Interface (PPI) IC 8255 will clear your concept.

Let’s check how you learn 8255 PPI with a simple quiz.

8255 PPI

MCQ on 8255 PPI

You may read those too…..

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Hi myself Subham Dutta, having 15+ years experience in filed of Engineering. I love to teach and try to build foundation of students. Try to make them imagine what they learn.

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