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.
8255A has three different operating modes –
- 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.
- 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.
- 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.
The following figure shows the architecture of the Intel 8255A – Programmable Peripheral Interface