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<title>Peripheral Interface Adapter</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Peripheral Interface Adapter</span></span>

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<p>A <b>Peripheral Interface Adapter</b> (PIA) is a <a href="Peripheral" title="Peripheral">peripheral</a> <a href="Integrated_circuit" title="Integrated circuit">integrated circuit</a> providing parallel I/O interfacing for <a href="Microprocessor" title="Microprocessor">microprocessor</a> systems.

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<div class="center"><span style="color:black;"><i><b>PIA pin configuration</b></i></span></div>

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</style><pre class="pre"><span style="color: #626971;">  ┌─────⊔︀─────┐

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

└───────────┘</span></pre></span>

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<div class="mw-heading mw-heading2"><h2 id="Description">Description</h2></div>

<p>Common PIAs include the <a href="Motorola" title="Motorola">Motorola</a> MC6820 and MC6821, and the <a href="MOS_Technology" title="MOS Technology">MOS Technology</a> MCS6520, all of which are functionally identical but have slightly different electrical characteristics. The PIA is most commonly packaged in a 40 pin <a href="Dual_in-line_package" title="Dual in-line package">DIP package</a>.

</p><p>The PIA is designed for glueless connection to the <a href="Motorola_6800" title="Motorola 6800">Motorola 6800</a> style <a href="Computer_bus" class="mw-redirect" title="Computer bus">bus</a>, 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 <a href="Handshake_(computing)" title="Handshake (computing)">handshaking</a> and <a href="Interrupt" title="Interrupt">interrupt</a> 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.

</p><p>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.<sup id="cite_ref-MC6821_1-0" class="reference"><a href="#cite_note-MC6821-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

</p><p>The MC6820 was used in the <a href="Apple_I" title="Apple I">Apple I</a> to interface the <a href="ASCII" title="ASCII">ASCII</a> keyboard and the display.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

It was also deployed in the 6800-powered first generation of <a href="Bally_Manufacturing" title="Bally Manufacturing">Bally</a> electronic pinball machines (1977-1985), such as <i><a href="Flash_Gordon_(pinball)" title="Flash Gordon (pinball)">Flash Gordon</a></i><sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

and <i><a href="Kiss_(pinball)" title="Kiss (pinball)">Kiss</a></i>.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup>

The MCS6520 was used in the <a href="Atari_8-bit_computers" title="Atari 8-bit computers">Atari 400 and 800</a><sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> and <a href="Commodore_PET" title="Commodore PET">Commodore PET</a><sup id="cite_ref-progpet_6-0" class="reference"><a href="#cite_note-progpet-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> family of computers (for example, to provide four joystick ports to the machine).

The <a href="Tandy_Color_Computer" class="mw-redirect" title="Tandy Color Computer">Tandy Color Computer</a> uses two MC6821s to provide I/O access to the video, audio and peripherals.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

<ul><li>Leventhal, Lance A. (1986). <i>6502 Assembly Language Programming 2nd Edition</i>. Osborne/McGraw-Hill. <style data-mw-deduplicate="TemplateStyles:r1238218222">

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</style><a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-07-881216-X</bdi>.</li></ul>

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<li id="cite_note-MC6821-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-MC6821_1-0">^</a></b></span> <span class="reference-text"><cite class="citation book cs1"><i>Advanced Information: 1.5 and 2.0 MHz Components for the M6800 Microcomputer System</i>. Austin, Texas: Motorola Semiconductor Products. April 1977. pp. <span class="nowrap">4–</span>6. ADI-429.</cite> 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.</span>

</li>

<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite class="citation book cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20110519052739/http://archive.computerhistory.org/resources/text/Apple/Apple.AppleI.1976.102646518.pdf"><i>Apple-1 Operation Manual</i></a> <span class="cs1-format">(PDF)</span>. 1976. p. 7. Archived from <a rel="nofollow" class="external text" href="http://archive.computerhistory.org/resources/text/Apple/Apple.AppleI.1976.102646518.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 2011-05-19<span class="reference-accessdate">. Retrieved <span class="nowrap">2016-03-05</span></span>.</cite></span>

</li>

<cite class="citation book cs1"><a rel="nofollow" class="external text" href="http://www.ipdb.org/machine.cgi?id=874"><i>Flash Gordon Manual</i></a>. Bally. 1981. p. 22.</cite></span>

</li>

<cite class="citation book cs1"><a rel="nofollow" class="external text" href="http://www.ipdb.org/machine.cgi?id=1386"><i>Kiss Manual</i></a>. Bally. 1979. p. 22.</cite></span>

</li>

<cite class="citation book cs1"><a rel="nofollow" class="external text" href="http://www.atarimania.com/documents/Sams_Computer_facts_Atari_800.pdf"><i>Sams Computerfacts Technical Service Data - Atari 800</i></a> <span class="cs1-format">(PDF)</span>. November 1984. p. IV.</cite></span>

</li>

<li id="cite_note-progpet-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-progpet_6-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFWest1982" class="citation book cs1">West, Raeto Collin (January 1982). <a rel="nofollow" class="external text" href="https://archive.org/stream/COMPUTEs_Programming_the_PET-CBM_1982_Small_Systems_Services"><i>Programming the PET/CBM</i></a>. COMPUTE! Books. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-942386-04-3</bdi><span class="reference-accessdate">. Retrieved <span class="nowrap">2020-04-05</span></span>.</cite></span>

</li>

<li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><cite id="CITEREFChris_Lomont2006" class="citation web cs1">Chris Lomont (July 2006). <a rel="nofollow" class="external text" href="http://www.roust-it.dk/coco/Lomont_CoCoHardware_2.pdf">"Chris Lomont's Color Computer 1/2/3 Hardware Programming"</a> <span class="cs1-format">(PDF)</span>. <i>www.lomont.org/Software/Misc/CoCo/Lomont_CoCoHardware.pdf</i><span class="reference-accessdate">. Retrieved <span class="nowrap">5 May</span> 2020</span>.</cite></span>

</li>

</ol></div></div>

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</style><div id="Interface_chips_from_MOS_Technology_and_second_source/clone_vendors116" style="font-size:114%;margin:0 4em"><a href="Memory-mapped_I/O" class="mw-redirect" title="Memory-mapped I/O">Interface</a> <a href="Integrated_circuit" title="Integrated circuit">chips</a> from <a href="MOS_Technology" title="MOS Technology">MOS Technology</a> and second source/clone vendors</div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="MOS_Technology_RRIOT" title="MOS Technology RRIOT">6530 RRIOT</a></li>

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