Peripheral Interface Adapter

Common PIAs include the Motorola MC6820 and MC6821, and the MOS Technology MCS6520, all of which are functionally identical but have slightly different electrical characteristics.

In 1976 Motorola switched the MC6800 family to a depletion-mode technology to improve the manufacturing yield and to operate at a faster speed.

The Peripheral Interface Adapter had a slight change in the electrical characteristics of the I/O pins so the MC6820 became the MC6821.

[2] It was also deployed in the 6800-powered first generation of Bally electronic pinball machines (1977-1985), such as Flash Gordon[3] and Kiss.

[4] The MCS6520 was used in the Atari 400 and 800[5] and Commodore PET[6] family of computers (for example, to provide four joystick ports to the machine).