Junkbox parts... - test-drb@ccmp.vtda.org

24 Apr 2007

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Subject: Re: Junkbox parts...
   From: Holger Veit <holger.veit at iais.fraunhofer.de>
   Date: Tue, 24 Apr 2007 09:37:48 +0200
     To: General Discussion: On-Topic Posts Only <cctech at classiccmp.org>

Allison schrieb:
  The question on junkbox z80 systems made me
remember that
 old 386 and 486 system besides providing a raft of 32kx8 SRAMS
 also had a keyboard interface chip..

 I have a few salvaged 8742(smae as 8242) from PC hardware
 of the AT class 80386-486 level.

 Without resorting to eraseing the Eproms (8742) and reprogramming 
 them I've wondered if..

 Can these parts (PC AT keyboard interface) can they be used for 
 small system as a interface from AT or PS2 keyboard to a 8bit micro.
 Right off I suspect yes.  However is there any information on how 
 to "talk" software wise to them as to what kind of results and 
 commands they take?

See http://www.arne.si/~mauricio/kbdfaq.html for abundant information on 
the keyboard,
and programming the controller. Basically, you connect it to a z80 the 
same way as it is done
in the PeeCee - wire it to i/o port 60/64h and use the same logic to 
program raw commands.
Normally, in homwbrew systems, people tend not to use a 8042 pulled from 
a scrap board but talk
to the keyboard directly, through the serial protocol described above. 
The keyboard itself typically
contained some 8048 controller to scan the kbd matrix. 
I've seen that and personally I'd like to isolate the system from the 
nasty scancode output from the keyboard so that the result looks like
simple ASCII 7bit.  I'd have to reprogram the 8742s to do that as the 
extracted parts only serve as a serial IO and buffer.

...
 I don't have the exact circuitry for the 8042 UPI
at hand right now, but 
the schematic can be
found in the IBM AT Technical Reference Manual. 
I have more than enough info on the 8742 itself, I use them for other 
applications.  The PC AT circuit is trivial and I have that as well.

Allison