MOS Technology 6522

The 6522 Versatile Interface Adapter (VIA) is an integrated circuit that was designed and manufactured by MOS Technology as an I/O port controller for the 6502 family of microprocessors. It provides parallel I/O, timers, and a shift register for serial communications. The 6522 was second sourced, by other companies including, Rockwell and Synertek.

The 6522 was widely used in computers of the 1980s, particularly Commodore's machines, and was also a central part of the designs of the Apple III, Oric-1 and Oric Atmos, BBC Microcomputer and Apple Macintosh. Video game platforms such as the Vectrex also used the 6522, as did the 1984 through 1989 Corvette digital dash cluster. A high speed, CMOS version, the W65C22[1], is produced by the Western Design Center (WDC).

The VIA contains 20 I/O lines, which are organised into two 8-bit bidirectional ports (or 16 general-purpose I/O lines) and four control lines (for handshaking and interrupt generation). The directions for all 16 general lines (PA0-7, PB0-7) can be programmed independently. The control lines can be programmed to generate an interrupt when activated (all four), latch the corresponding I/O port (CA1 and CB1), automatically generate handshaking signals for devices on the I/O ports, or output a plain High or Low signal.

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