Xerox D-series workstations

From: Eric Smith <>
Date: Mon Nov 8 02:03:49 1999

Kevin Schoedel <> wrote:
> "The keyboard/interface uses the receive half of the i8251A interface
> chip" suggests it's one-way communication. "... receive from the
> keyboard as a differential signal pair by a 75176A receiver chip." I
> don't know; does this imply RS232-compatible levels?

No, it's an EIA-422 differential pair. Not really even close to EIA-232,
although it wouldn't take too much circuitry to convert. If you had a
device with an EIA-232 output that you wanted to hook up to the 6085
keyboard port, you'd just need an EIA-232 receiver section from a part
such as a MAX232, and an EIA-422 (or EIA-485) driver section from a part
like a 75176 or MC3487.

> "... asynchronous
> serial interface with a data rate of 9600bps". I do not see the protocol
> documented, but by the time you get around to your machine, I should be
> able to hang my keyboard and mouse on some serial port and/or logic
> analyzer to work it out.

If I had to hazard a guess, I'd suspect that it sends non-ASCII keycodes,
with a separate make and break code for each key.
Received on Mon Nov 08 1999 - 02:03:49 GMT

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