Alto-1822 Interface

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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 CPU bus, and used custom microcode to move data to and from main memory. It was full-duplex, but included no buffering other than input and output shift registers. It could operate in both models of the Alto (Alto I and II).

Physically, it was a single PCB (initial prototypes were wire-wrapped) 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 Maxc2 front end to connect to the ARPANET for NCP, on PUP gateways to talk to PRUs, and apparently eventually on the Alto ARPANET IP 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