Editing Peripheral Interface Adapter

{{Short description|Input/output chip for 8-bit microprocessors}}
[[File:Motorola MC6820L MC6821L.jpg | thumb|right | Motorola MC6820 and MC6821 Peripheral Interface Adapters]]
A '''Peripheral Interface Adapter''' (PIA) is a [[peripheral]] [[integrated circuit]] providing parallel I/O interfacing for [[microprocessor]] systems.
[[File:MOS 6520.jpg | thumb|right | MOS 6520]]
<div class="floatright" style="border: 1px solid #828991;background-color: #f8f9fa;padding:0.2em;font-size:88%;color:red;">
{{center|{{font color|black|'''''PIA pin configuration'''''}}}}
{{resize|80%|{{Pre|{{font color|#626971|&nbsp;   ┌─────⊔︀─────┐
Vss ┤ 1       40├ CA1
PA0 ┤ 2       39├ CA2
PA1 ┤ 3       38├ !IRQA
PA2 ┤ 4       37├ !IRQB
PA3 ┤ 5       36├ RS0
PA4 ┤ 6       35├ RS1
PA5 ┤ 7       34├ !RES
PA6 ┤ 8       33├ D0
PA7 ┤ 9       32├ D1
PB0 ┤10       31├ D2
PB1 ┤11       30├ D3
PB2 ┤12       29├ D4
PB3 ┤13       28├ D5
PB4 ┤14       27├ D6
PB5 ┤15       26├ D7
PB6 ┤16       25├ E
PB7 ┤17       24├ CS1
CB1 ┤18       23├ !CS2
CB2 ┤19       22├ CS0
Vcc ┤20       21├ R/!W
    └───────────┘}}}}}}
</div>

==Description==
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.  The PIA is most commonly packaged in a 40 pin [[Dual in-line package|DIP package]].

The PIA is designed for glueless connection to the [[Motorola 6800]] style [[Computer bus|bus]], 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 [[Handshake (computing)|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 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.<ref name = "MC6821">{{Cite book | title = Advanced Information: 1.5 and 2.0 MHz Components for the M6800 Microcomputer System. | pages = 4–6 | publisher = Motorola Semiconductor Products | location = Austin, Texas | date = April 1977 | id = ADI-429}} 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.</ref>

The MC6820 was used in the [[Apple I]] to interface the [[ASCII]] keyboard and the display.<ref>{{Cite book | title = Apple-1 Operation Manual | page = 7 | date = 1976 | url = http://archive.computerhistory.org/resources/text/Apple/Apple.AppleI.1976.102646518.pdf | access-date = 2016-03-05 | archive-url = https://web.archive.org/web/20110519052739/http://archive.computerhistory.org/resources/text/Apple/Apple.AppleI.1976.102646518.pdf | archive-date = 2011-05-19 | url-status = dead }}</ref>
It was also deployed in the 6800-powered first generation of [[Bally Manufacturing|Bally]] electronic pinball machines (1977-1985), such as ''[[Flash Gordon (pinball)|Flash Gordon]]''<ref>
{{Cite book | title = Flash Gordon Manual | page = 22 | date = 1981| publisher = Bally | url = http://www.ipdb.org/machine.cgi?id=874}}</ref>
and ''[[Kiss (pinball)|Kiss]]''.<ref>
{{Cite book | title = Kiss Manual | pages = 22 | date = 1979| publisher = Bally | url = http://www.ipdb.org/machine.cgi?id=1386}}</ref>
The MCS6520 was used in the [[Atari 8-bit computers|Atari 400 and 800]]<ref>
{{Cite book | title = Sams Computerfacts Technical Service Data - Atari 800 | page = IV | date = November 1984 | url=http://www.atarimania.com/documents/Sams_Computer_facts_Atari_800.pdf}}</ref> and [[Commodore PET]]<ref name="progpet">{{cite book|title=Programming the PET/CBM|last=West|first=Raeto Collin|publisher=COMPUTE! Books|isbn=0-942386-04-3|url=https://archive.org/stream/COMPUTEs_Programming_the_PET-CBM_1982_Small_Systems_Services|access-date=2020-04-05|date=January 1982}}</ref> 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.<ref>{{cite web|url=http://www.roust-it.dk/coco/Lomont_CoCoHardware_2.pdf|work=www.lomont.org/Software/Misc/CoCo/Lomont_CoCoHardware.pdf|title=Chris Lomont's Color Computer 1/2/3 Hardware Programming|access-date=5 May 2020|author=Chris Lomont|date= July 2006}}</ref>

==References==
* Leventhal, Lance A. (1986). ''6502 Assembly Language Programming 2nd Edition''. Osborne/McGraw-Hill. {{ISBN|0-07-881216-X}}.
{{Reflist}}
{{MOS Interface}}

[[Category:Input/output integrated circuits]]


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