DESCRIPTION
The Intel 8255A is a general purpose programmable l/O device designed for use with Intel microprocessor3. It has 24 I/O pins which may be individually programmed in 2 groups of 12 and used in 3 major modes of operation. In the first mode(MODE 0), each group of 12 1/O pins may be programmed in sets of 4 to be inout or output. In MODE 1, the second mode, each group may be programmed to have 8 lines of input or output. Of the remaining 4 pins,3 are used for handshaking and interrupt control signals. The third mode of operation (MODE 2) is a bidirectional bus mode which uses 8 lines for a bidirectlonal bus, and 5 lines, borrowing one from the other group, for handshaking.
(Picture: Pinout)