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Path: utzoo!linus!decvax!bellcore!petrus!sabre!python!michael
From: michael@python.UUCP (M. Cain)
Newsgroups: net.micro.6809
Subject: 8-bit A/D under OS9
Message-ID: <189@python.UUCP>
Date: Tue, 1-Apr-86 08:36:36 EST
Article-I.D.: python.189
Posted: Tue Apr  1 08:36:36 1986
Date-Received: Wed, 2-Apr-86 20:19:19 EST
Distribution: net
Organization: Bell Communications Research
Lines: 34

I have recently been experimenting with the Coco Max
8-bit A/D converter using OS9.  The documentation is
scanty -- "the module is addressed at 0xff90" is the
extent of it -- but I have had some success.  The
following code fragment works:

point = (char *)0xff90;
for (i=0; i<4; i++) mouse[i] = *point++;

After the loop, mouse[1] contains a vertical coordinate,
mouse[2] a horizontal, and mouse[3] indicates the status
of the button.  The advantage of the 8-bit A/D values is,
of course, that it is now possible to point to individual
pixels on a high-resolution graphics screen without
resorting to "sliding windows" or the like.

The following attempts at efficiency all break the code:

  - Unrolling the loop,
  - Skipping the "wasted" access of 0xff90,
  - Declaring mouse to be an array of type char rather
    than type int.

I tried taking the cartridge apart, but it appears that
unreasonable amounts of force are needed, and I didn't
want to risk any damage to the internals.  Does anyone
know what's inside, and how it's being used?

Finally, I find that it is necessary for any programs that
poll the module to make a sleep(n) call at the beginning,
with n a small integer -- if I don't, the disk drive motor
continues to run, apparently forever.

Michael Cain