The Intel 8255 (or i8255/onkyo tx 8255) Programmable Peripheral Interface (PPI) chip was developed and manufactured by Intel for the Intel 8080 microprocessor in the early 1970’s. The 8255A is a programmable universal I / O device that allows the transfer of I / O data to an I / O interrupt when needed. It can be used with almost any microprocessor. It consists of three bidirectional 8-bit I / O ports (24 I / O lines) that can be configured as needed.

Ports of 8255A

The 8255A has three ports, PORT A, PORT B, and PORT C.

  • Port A contains an 8-bit output latch / buffer and an 8-bit input buffer.
  • Port B is similar to PORT A.
  • Port C can be divided into two parts by the control word, ie, lower PORT C (PC0-PC3) and higher PORT C (PC7-PC4).

These three ports are then subdivided into two groups, ie group A includes ports A and higher C. Group B includes ports B and lower C. These two groups of Intel 8255 programmable peripheral interface can be programmed in three different modes, i. H. d. That the first mode is called a mode. 0 is the second mode as mode 1 and the third mode designated as mode 2.

Operating Modes

8255A has three different operating modes –

  1. Mode 0 – In this mode, ports A and B are used as two 8-bit ports and port C as two 4-bit ports. Each port can be programmed either in input mode or in output mode with the outputs disabled and the inputs not disabled. Ports have no interrupt capability.
  2. Mode 1 – In this mode, ports A and B are used as 8-bit I / O ports. They can be configured as input or output ports. Each port uses three lines of port C as handshaking signals. Inputs and outputs are blocked.
  3. Mode 2 – In this mode, port A can be configured as a bidirectional port. Port B is in Mode 0 or Mode 1. Port A uses five signals from Port C as handshake signals for data transmission. The remaining three signals from port C can be used either as a simple I / O or as a handshake for port B.

Features of 8255A

The main features of 8255A are:

  • It consists of 3 IO-8-bit ports, namely PA, PB and PC.
  • The address / data bus must be scaled externally.
  • It is TTL compatible.
  • It has improved the DC driving ability.

8255 architecture

The following figure shows the architecture of the Intel 8255A – Programmable Peripheral Interface