A Peripheral Interface Adapter (PIA) is a

peripheral A peripheral device, or simply peripheral, is an auxiliary hardware device that a computer uses to transfer information externally. A peripheral is a hardware component that is accessible to and controlled by a computer but is not a core compo ...

integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

providing parallel I/O interfacing for

microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...

systems.

Description

Common PIAs include the

Motorola Motorola, Inc. () was an American multinational telecommunications company based in Schaumburg, Illinois. It was founded by brothers Paul and Joseph Galvin in 1928 and had been named Motorola since 1947. Many of Motorola's products had been ...

MC6820 and MC6821, and the

MOS Technology MOS Technology, Inc. ("MOS" being short for Metal Oxide Semiconductor), later known as CSG (Commodore Semiconductor Group) and GMT Microelectronics, was a semiconductor design and fabrication company based in Audubon, Pennsylvania. It is ...

MCS6520, all of which are functionally identical but have slightly different electrical characteristics. The PIA is most commonly packaged in a 40 pin DIP package. The PIA is designed for glueless connection to the

Motorola 6800 The 6800 ("''sixty-eight hundred''") is an 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System (later dubbed ''68xx'') that also included serial and parall ...

style

bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a motor vehicle that carries significantly more passengers than an average car or van, but fewer than the average rail transport. It is most commonly used ...

, and provides 20 I/O lines, which are organised into two 8-bit bidirectional ports (or 16 general-purpose I/O lines) and 4 control lines (for handshaking and

interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted ...

generation). The directions for all 16 general lines (PA0-7, PB0-7) can be programmed independently. The control lines can be programmed to generate interrupts, automatically generate handshaking signals for devices on the I/O ports, or output a plain high or low signal. 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. The MC6820 became the MC6821 because the electrical characteristic of PA0–7 and PB0–7 pins changed slightly. The typical Input High Current went from -250 μAdc to -400 μAdc and the Input Low Current went from 1.0 mAdc to 1.3 mAdc. The MC6820 was used in the

Apple I The Apple Computer 1 (Apple-1), later known predominantly as the Apple I, is an 8-bit personal computer designed by Steve Wozniak and released by the Apple Computer Company (now Apple Inc.) in 1976. The company was initially formed to ...

to interface the

ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...

keyboard and the display. It was also deployed in the 6800-powered first generation of Bally electronic pinball machines (1977-1985), such as ''

Flash Gordon Flash Gordon is the protagonist of a space adventure comic strip created and originally drawn by Alex Raymond. First published January 7, 1934, the strip was inspired by, and created to compete with, the already established ''Buck Rogers'' ...

'' and ''

Kiss A kiss is the touching or pressing of one's lips against another person, animal or object. Cultural connotations of kissing vary widely; depending on the culture and context, a kiss can express sentiments of love, passion, romance, sex ...

''. The MCS6520 was used in the Atari 400 and 800 and

Commodore PET The Commodore PET is a line of personal computers produced starting in 1977 by Commodore International. A single all-in-one case combines a MOS Technology 6502 microprocessor, Commodore BASIC in read-only memory, keyboard, monochrome monitor ...

family of computers (for example, to provide four joystick ports to the machine). The Tandy Color Computer uses two MC6821s to provide I/O access to the video, audio and peripherals.

References

* Leventhal, Lance A. (1986). ''6502 Assembly Language Programming 2nd Edition''. Osborne/McGraw-Hill. . Input/output integrated circuits {{compu-stub