Apple II+ Keyboard Encoder

From: Richard Erlacher <edick_at_idcomm.com>
Date: Mon Aug 20 15:06:58 2001

It's a George-Risk keyboard, made by the company in Nebraska, IIRC, and the
encoder is a custom-coded version of a standard GI product. There's a fix
inherently possible, but it involves wire and solder ... BEWARE!

see below, plz.

Dick
----- Original Message -----
From: "Foust, Daniel" <DanielF_at_McLean.gov>
To: <classiccmp_at_classiccmp.org>
Sent: Monday, August 20, 2001 12:40 PM
Subject: Apple II+ Keyboard Encoder


> My Apple II+ Keyboard Encoder card is faulty and I would like to know if
> it's fixable. I've tried several different keyboards and 2 motherboards so
> I'm certain it's the encoder. I've run a keyboard diagnostic and it is
> acting as though the control key is always pushed but it is not. It does it
> with 3 different keyboards so it's not a "stuck key" problem. Any ideas or
> help much appreciated. Thank you.
>
If you know precisely what the code produced for each key is, which shouldn't be
a problem, you need simply program an MCU to produce that code set and then
haywire it in place of the existing and apparently defective encoder. IIRC, the
encoder was a General Instruments model, albeit custom coded, but one can take
the output generated by another version of the same device and translated it via
a lookup table in EPROM. This has to be done externally to the Apple][+, of
course, but its not difficult to manage.

You could also put a "band-aid" on it by programming a PIC or similar MCU to
look only at the existing incorrect key codes and implement a firmware repair
based on which key combinations are apparently wrong.

I had to wrestle with this problem once, admittedly a long time ago, but the fix
is still valid. If your MCU has enough ROM to look up a value for each scanned
key in combination with the normally isolated keys, e.g. shift, ctl, alt, cap's
lock (if there is one), then it's quite straightforward.
Received on Mon Aug 20 2001 - 15:06:58 BST