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Peripheral Interface Adapter
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==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>
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