Subject: Re: Keyboard PS/2 to Parallel converter
From: "Roy J. Tellason" <rtellason at verizon.net>
Date: Mon, 07 Jan 2008 18:51:24 -0500
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
On Monday 07 January 2008 11:54, Fred Cisin wrote:
It would seem that the cheapest way to do it is a
discardable PC.
Input character
print it
loop
There was some project article in Byte way back when, by Steve Ciarcia,
which provided a peecee-type keyboard input (AT rather than PS/2 but that
shouldn't make that much difference). The circuit to deal with this was very
simple and elegant, though I can't remember any more just how it was done.
It used a Z80 and a PPI rom and ram. At the time that was a easy small
design but still far more cpu than needed. The task is PIC or 8048 sized.
Fornm the At days to current the PS2 keyboard is handled with an 8042
(discrete or embedded) which is a slave bus verion of the 8048..
There are PIC designs for this out there as well as Atmel ATmega. Check
their sites.
He didn't use a UART or similar, though, just a
couple of MSI chips. And I
remember thinking then how it wouldn't be all that hard to stuff an eprom
between the output of that circuit (which gave you keycodes rather than
characters) and have it spit out ASCII.
Ah, you do you handle the key down codes and the key up codes?
Perhaps one of these days I'll run across the article again.
I have it burried somewhere. It does not translate well to an PS2
keyboard as the XT keyboard used for that has slower IO rate and
different keyscan. It would be a pain to do in simple logic as you
need at least a state machine.
Allison
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