Xref: utzoo comp.sys.amiga:25088 comp.sys.amiga.tech:2392
Path: utzoo!utgpu!attcan!uunet!cbmvax!ditto
From: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech
Subject: Re: Amiga Mouse info needed
Summary: Clock & Direction for counter
Keywords: Amiga Mouse Info Pinouts
Message-ID: <5211@cbmvax.UUCP>
Date: 10 Nov 88 07:53:43 GMT
References: <7804@bloom-beacon.MIT.EDU> <1093@dukeac.UUCP>
Reply-To: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Organization: Commodore Technology, West Chester, PA
Lines: 27

In article <1093@dukeac.UUCP> sgt@dukeac.ac.duke.edu (Stephen G. Tell)
writes [ a decent description of how mouse quadrature works ]:
>At any transition of any line, look at the other line to tell you
>what direction you're going as follows:

... but then describes a really icky way of interpreting these signals
in hardware ...

>How to do this in hardware:
>One way that I've seen it done is to generate a short pulse
>with a one-shot on both transitions of both lines (4 one shots,
 [ ... and lots of other awful stuff ... ]

There is a very simple way:  Use one signal as an edge-triggered clock
for an up/down counter, and the other signal is simply the counter's
direction input.  I'm pretty sure that's the way the Amiga does it.

It doesn't matter which signal is which, or whether you count rising
or falling edges, or whether the direction is UP/DOWN* or DOWN/UP*;
changing any of these will simply reverse the counting direction.
-- 
					-=] Ford [=-

"The number of Unix installations	(In Real Life:  Mike Ditto)
has grown to 10, with more expected."	ford@kenobi.cts.com
- The Unix Programmer's Manual,		...!sdcsvax!crash!elgar!ford
  2nd Edition, June, 1972.		ditto@cbmvax.commodore.com