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Introduction to 8255 PPI (Programmable peripheral interface)

Introduction to 8255 PPI: In this article, we are going to study about what is 8255 PPI (Programmable peripheral interface) in the world of computers and processors? How it functions and will study its different characteristics?
Submitted by Monika Sharma, on August 21, 2019

Introduction of the 8255 PPI

The 8255 PPI (Programmable peripheral interface) is a device through which we can achieve the basic method of communication between humans or machines and the microprocessor. Here, the PPI stands for "Programmable Peripheral Interface". As the name itself suggests, it is a peripheral device for a machine which is programmed to act as an interface, and the 8255 PPI is an interface between the microprocessors (basically 80- microprocessor series) and the input-output devices, ADC (Analog to Digital Converters), DAC (Digital to Analog Converters), etc.

Characteristics of the 8255 PPI

The following are the characteristics of the 8255 PPI (Programmable peripheral interface),

  • The 8255 IC is a Programmable Peripheral Interface (PPI) which is used to interface the microprocessors with the various devices.
  • The 8255 PPI chip is a 40 pin IC.
  • In the 8255 IC, there are 24 input/ output lines.
  • In this IC, the input/ output lines are divided into e different ports: Port A, Port B, and Port C. Each port contain 8 data lines. The Port C is further divided into two different parts as C- upper and C- lower. The Port A and the Port C- upper together form the Group A and the Port B and the Port C- Lower Together form the Group B.

The following diagram illustrates the division of 8255 i/o lines into different ports,

Introduction to 8255 PPI
  • There are two modes in which the 8255 PPI operates. The one is the BSR mode (which stands for Bit Set Reset) and the other one is the IO mode (which stands for Input- Output).
  • There are further 3 modes for the IO mode: mod- 0, mod- 1 and mod- 2.
  • It operates on +5V of the voltage supply.
  • The 8255 contains 1 pin for voltage supply and 1 pin is used for ground voltage.
  • The operations of the 8255 PPI are controlled via the 8-bit binary code which is stored in the Control word. The control word refers to 8 pins (from 27 to 34) which store the 8-bit binary code in it.
  • The contents of the control word decide which mode will be used, which lines will be used and what action will be performed. Hence, the control word depends upon the mode which is being used.
  • The handshaking procedure can be followed using the 8255 PPI.





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