7 Nov
1999
7 Nov
'99
6:03 p.m.
Kevin Schoedel <schoedel(a)kw.igs.net> 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.