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From: ford@crash.CTS.COM (Michael Ditto)
Newsgroups: comp.sys.amiga
Subject: Re: Keyboard parallelogram fix?
Message-ID: <1814@crash.CTS.COM>
Date: Sun, 4-Oct-87 04:21:04 EDT
Article-I.D.: crash.1814
Posted: Sun Oct  4 04:21:04 1987
Date-Received: Wed, 7-Oct-87 06:25:50 EDT
References: <482@esunix.UUCP> <2419@cbmvax.UUCP> <4047@zen.berkeley.edu>
Reply-To: ford@crash.CTS.COM (Michael Ditto)
Organization: Crash TS, El Cajon, CA
Lines: 46
Keywords: keyboard rollover
Summary: A1000 as expected; A500 is bizzarre; A2000 is The Right Thing

In article <4047@zen.berkeley.edu> bryce@hoser.berkeley.edu.UUCP (Bryce Nesbitt) writes:
>In article <2419@cbmvax.UUCP> grr@cbmvax.UUCP (George Robbins) writes:
 [ discussion about parallelogram problem ]
>On the A1000 I'm typing upon, holding "f" and "r" then pressing either
>"l" or "o" produces both "l" and "o".  Sure looked like both to the
>keyboard!
>On the A500 next door, holding "f" and "r" then pressing either "l" or
>"o" produces nothing.

This is interesting.  The A1000 exhibits the normal, expected, behavior of
a simple short-the-row-to-the-column matrix keyboard.  The A500 seems to
be hardwarily the same, with firmware to ignore ambiguous combinations.  This
is disappointing, but better than the A1000.

>Typing "fro", holding each key down produces:
>
>A1000	-	frlo
>A500	-	fr
>

I have an A2000 (German version), on which I will make the same test... the
result:

A2000   -       fro

That's right, the A2000 (this one, anyway) does exactly and undeniably The
Right Thing!  It has true N-key rollover; I can type a whole sentence
without lifting any key I press until I need to re-use it (or run out of
ingers).

Now MY big question is:  Does the B2000 work this way as well??  If not, I
may have to beg Commodore to let me keep this A2000.  I get very annoyed
when I type on the A1000; it reminds me of the TRS-80 :-).


BTW, the cause of the problem is obvious if you take a moment to figure out
how a normal matrix keyboard works; the fixes are not so obvious, but one is
to put a diode in series with each keyswitch.  Another is to use certain
types of "active" keyboard switches that have "enable" and "output" pins
and do not pass any signal from the output to the "enable" input.  Neither
is practical as a retrofit modification.
-- 

Michael "Ford" Ditto				-=] Ford [=-
P.O. Box 1721					ford@crash.CTS.COM
Bonita, CA 92002				ford%oz@prep.mit.ai.edu