PC/XT keyboard for 820-II?
Jeff Jonas
>writes:
>>Ken (glo...@delphi.com) wrote:
>>:Can anyone recommend a place to find specs on a PC/XT keyboard? I have a Xerox
>>:820-II that needs a new keyboard, and I would like to build an adapter. I think
>>:they are available commercially, but $129 seems kind of steep. I don't want a
>>:schematic (for an adapter), I would prefer to try to make one on my own. I just
>>:want to know where to find out what happens when a key is pressed on an XT key-
>>:board. Thank you.
Ya, considering that entire systems are under $50 at flea markets
(when they're not otherwise free), I agree that it's not spend more
than $20 on a keyboard.
>>The Undocumented PC, by Frank Van Gilluwe, would be a good place to start.
>>It doesn't deal with the hardware within the keyboard, but it's pretty
>>clear about what happens at the m/b end.
>>Will (c...@crash.cts.com)
Hmmmm, I wonder -- what does it say about that 40 pin chip
near the keyboard connector. Does that give parallel ASCII out?
Where is the keyboard converted to ASCII?
>I don't think the PC/XT or PC/AT keyboards are good places to
>start. Although they are cheap, they deliver key codes, not ASCII
>like most CP/M computer want. The data stream is at 1200
>baud, but if you were to use a PC keyboard you would need to
>write software to convert the key codes to ASCII. Not an
>inconsiderable task, considering that pressing even the left and
>right Shift Keys results in different key codes being sent to the
>CPU.
I bought many surplus keyboards and most were not in cases,
or were in large cases for desktop use, never laptop like the PC.
Nearly every keyboard I bought surplus had some oddity or eccentricity,
such as punctuation in strange locations, upper case only, etc.
>I think you'd do better looking for an ASCII keyboard in a surplus
>electronics store or even thrift store. I do have keyboards
>from the Sanyo MBC-550 that do put out ASCII code at 1200 baud,
>(for $17 + postage = ~$20), but that would not be the end of your
>problems. Best of all, of course, would be to find a keyboard
>made for the Big Board or its compatibles, perhaps from someone
>on the net. Perhaps someone has already approached you with
>one.
>Victor R. Frank, K6FV (fr...@sneezy.sri.com)
I'm in no position to tackle this, but wouldn't a Z8 with the piggyback ROM
or some EPROM microcontroller be just right for converting the
serial keystrokes into parallel ASCII? A single chip solution!
A Z80 seems overkill but at today's prices it's cheap enough.
Imagine - what once was an entire computer being delegated
as part of a keyboard!
Seriously - there are many old terminals and computers that used
parallel keyboard that could be retrofitted with PC keyboards
with such an adapter. I'm surprised that I don't know of any.
Perhaps the Circuit Cellar folks have some leads?
(I wish they were on internet).
--
Jeffrey Jonas
je...@panix.com