Programmable Peripheral Interface (PPI) IC 8255

Here we see how can we use Programmable Peripheral Interface (PPI) IC 8255 for data transfer? As we know Programmable Peripheral Interface (PPI) IC 8255 is used to interface input and output device with microprocessor. The various methods of data transfer from the microprocessor to output devices or vice-versa has already been discussed in my earlier posts. Now we come to discuss a special interface circuits, known as peripheral interface circuits are to be used for this purpose. The interfacing devices (IC 8255) may be classified into two categories namely general purpose peripherals and special purpose peripherals.

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

In above, we see that we may be classified the interfacing devices into two categories namely general purpose peripherals and special purpose peripherals. So general purpose peripherals are:

  • Programmable Peripheral Interface (PPI)
  • Programmable Interval Timer
  • Programmable Interrupt Controller
  • Programmable DMA Controller
  • Programmable Communications Interface.

And the special purpose peripherals used for interfacing a microprocessor to a specific type of I/O device are:

  • Programmable Keyboard and Display Interface
  • Programmable Hard Disk Controller
  • Programmable Floppy Disk Controller

In this post we will confine to the discussion of Programmable Peripheral Interface (PPI) IC 8255 A and its application.

DETAILS OF PPI IC 8255A

If we take example of microprocessor 8085, then we can see in 8085 microprocessor it do 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 (PPI) IC 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 interfaced to the microprocessor through the input/output port. The input/output port is either nonprogrammable or programmable. A non-programmable port can either be connected in input mode or output mode. If both input and output devices are to be connected to the microprocessor two separate non-programmable ports are to be used, one for input device and other for the output device.

 The INTEL 8255A is a programmable port device. It is most versatile Programmable Peripheral Interface which may be connected to almost any microprocessor. This IC is widely used and 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 are shown in figures.

Programmable Peripheral Interface (PPI) IC 8255

The IC 8255 A has three 8-bit ports:

Port-A

Port-B and Port-C

The port-C can be used into two 4-bit ports represented as Port CUpper and Port CLower .

Hope this discussion on Programmable Peripheral Interface (PPI) IC 8255 will clear your concept.

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