Fact is, the serial protocol for communicating with your 'AT keyboard is
widely understood and well documented. I'm sure anyone who could program an
older 8-bit micro could program a PIC or other single-chipper, like the
87C42 which I believe is still made, to do what the old 8042 does. If you
get an 8742, I don't think they even have a code protection bit.
Given that you have too much principle, and perhaps not enough interest, to
replicate the 8042 ( a clever choice of chips ) you could simply decode the
binary you do get from the keyboard with a lookup table.
Dick
-----Original Message-----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Sunday, April 04, 1999 6:31 PM
Subject: Re: homemade computer for fun and experience...
>>
>> > True. But AFAIK the AT keyboard host interface was never implemented in
>> > TTL (it always used a programmed 8042 microcontroller), so it's a
little
>> > harder to build from scratch.
>>
>> If what you're trying to do is interface the AT keyboard to some custom
>> controller that doesn't need to be otherwise AT-compatible, there's no
>> reason why you need the 8042. The AT keyboard interface is not
particularly
>> harder to implement than the XT interface was. I've written code for
several
>> products that bit-banged it on a microcontroller.
>
>Absolutely. BUT : if you are making a homebrew machine, the last things
>you need are (a) I/O that's timing critical (at least not for the
>keyboard) or (b) a microcontroller that you have to program and debug.
>
>And then, as you said below, the AT keyboard protocol is not that well
>documented. The XT is a little better documented, if only because there's
>a circuit using standard chips (plain TTL chips) that accepts XT keyboard
>input. You can work out any odd bits of the protocol from that.
>
>Alas IBM never published the 8042 ROM source, so you can't use that as a
>reference.
>
>>
>> The AT keyboard interface protocol is really a pathetic design, though.
It's
>
>I'll not argue with that.
>
>> a pain in the ass to deal with, and it's not well documented anywhere
(even
>
>The documentation is not brilliant, but you can figure out how to talk to
an
>AT keyboard from the info in the TechRef if you have to. Not an ideal
>first project, though.
>
>-tony
>
Received on Sun Apr 04 1999 - 19:52:36 BST