View source for Alto-1822 Interface

The '''Alto-1822 Interface''' was an [[1822 interface]] for the [[Xerox Alto]]. In common with almost all high data rate Alto devices, it was connected to the Alto [[Central Processing Unit|CPU]] bus, and used custom [[microcode]] to move data to and from [[main memory]]. It was [[full-duplex]], but included no [[buffer]]ing other than input and output [[shift register]]s. It could operate in both models of the Alto (Alto I and II).

Physically, it was a single [[printed circuit board|PCB]] (initial prototypes were [[wire-wrap]]ped) which plugged into the main [[backplane]]. The 1822 interface was run through a [[flat cable]] from a row of contacts on the back edge of the PCB to a connector on the Alto's back panel, and thence via a cable to the entity to be connected. Both LH and DH 1822 interface variants were supported.

It was used on the [[Maxc|Maxc2]] [[front end]] to connect to the [[ARPANET]] for [[Network Control Program|NCP]], on [[PARC Universal Packet|PUP]] [[router|gateways]] to talk to [[Packet Radio Network‎|PRUs]], and apparently eventually on the Alto ARPANET [[Internet Protocol|IP]] [[router|gateway]].

A great deal of information about it has survived in the Alto archive (see below): informal documentation; hardware engineering details; microcode; higher-level software which used it.

==External links==

* [https://xeroxalto.computerhistory.org/Indigo/Alto-1822/.index.html Alto 1822 interface information]
** [https://xeroxalto.computerhistory.org/Indigo/Alto-1822/extra.dm!1_/.AIDesign.memo.html Alto-1822 Interface Request for Comments] January 2, 1978
** [https://xeroxalto.computerhistory.org/Indigo/Alto-1822/extra.dm!1_/.AIupdate.memo.html New microcode, other changes] January 26, 1978
** [https://xeroxalto.computerhistory.org/Indigo/Alto-1822/extra.dm!1_/.ainewdesign.memo.html New, Up-to-date stuff] February 7, 1978
** [https://xeroxalto.computerhistory.org/Indigo/Alto-1822/extra.dm!1_/.AISWSpec.memo.html Microcode & Emulator Interface] March 30, 1978
** [https://xeroxalto.computerhistory.org/Indigo/Alto-1822/extra.dm!1_/.aipcintcable.memo.html Alto-1822 PC Board Internal Cable] May 19, 1978
** [https://xeroxalto.computerhistory.org/Indigo/Alto-1822/extra.dm!1_/.aicables.memo.html Alto 1822 Interface cable descriptions] November 5, 1978
** [https://xeroxalto.computerhistory.org/Indigo/Alto-1822/extra.dm!1_/.installation.memo.html Installation and Testing] March 13, 1981
* John Shoch and Larry Stewart, [https://www.rfc-editor.org/ien/scanned/ien78.pdf Internetwork experiments with the Bay Area Packet Radio Network], IEN 78, January 1979 - has an image of the Alto-1822 Interface

[[Category: 1822 Interfaces]]