82C55 CMOS Programmable Peripheral Interface

The Intel 82C55A is a CHMOS-enabled variant of the industry-standard 8255A general-purpose programmable I/O device that is compatible with all Intel and most other microprocessors. Its goal is to interface peripheral equipment to the microcomputer system bus as a general-purpose I/O component. The system software programs the 82C55A’s functional configuration, thus no extra logic is required to interface peripheral devices or structures.

It has 24 I/O pins that may be programmed independently in two groups of 12 and used in three different modes of operation. The NMOS 8255A and 8255A-5 are pin compatible with the 82C55A. Each group of 12 I/O pins was configured as inputs or outputs in groups of 4 and 8 in MODE 0. Each group in MODE 1 was programmed with eight lines of input or output. Also used for handshaking and interrupt control signals are three of the remaining four pins. MODE 2 is a bi-directional strobed bus configuration. The 82C55A is made with Intel’s superior CHMOS III technology, which offers low power consumption and performance comparable to or better than NMOS. Also available are 40-pin DIP and 44-pin plastic leaded chip carrier (PLCC) packages for the 82C55A.

The 82C55A is connected to the system data bus through this 3-state bidirectional 8-bit buffer. As a result, data is communicated or received by the buffer when the CPU executes input or output instructions. The data bus buffer also transfers control words and status information. The IC mainly operates on three basic modes of operation selected by the system software

• Mode 0 – Basic input/output
• Mode 1 – Strobed Input/output
• Mode 2 – Bi-directional Bus