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From: sgt@dukeac.UUCP (Stephen G. Tell)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech
Subject: Re: Amiga Mouse info needed
Summary: what the quadrature signals are and one hardware decoding scheme.
Keywords: Amiga Mouse Info Pinouts
Message-ID: <1093@dukeac.UUCP>
Date: 8 Nov 88 20:39:16 GMT
References: <7804@bloom-beacon.MIT.EDU>
Reply-To: sgt@dukeac.ac.duke.edu (Stephen G. Tell)
Organization: Academic Computing, Duke University, Durham, NC
Lines: 77

I build somthing to deal with mouse signals once, and I think I remember
it enough to explain how it works.

I don't have a manual handy, so I don't know the pinouts, but if you
have the simple introductory manual, its good enough with a bit of
explaining:
Power & ground are obvious
The amiga supports 3-button mice on the 9-pin plug, The mouse that
comes with it uses button 1 and 3 inputs, (I think)
I've actually got a 3-button mouse on my machine, but haven't fooled around
with software to use the new middle button.

The horizontal (vertical) quadrature pins tell you speed and direction
for the two axes.  I'll speak in terms of horizontal, vertical is
the same.

The two horizontal signals are basicly the same signal; reversing them
changes the apparent left/right direction.  I forget what the manual's
pinout calls them exactly, but it leads you to believe that they
are somehow fundamentaly different.

If you have a dual-trace scope, hook power to the mouse and look at the
two horizontal quadrature signals as you move back and forth, then the
following should become clear:

Either signal alone gives you speed information as a certain number
of pulses per unit distance the mouse is moved.
The relative phase of the two signals tells you what direction
you're moving.

If we call the two signals A and B, they might look like this for
leftward movement:

   ____       _____       _____
A      |_____|     |_____|     |_____
  __       _____       _____       __
B   |_____|     |_____|     |_____|

And like this for rightward movement:
  __       _____       _____
A   |_____|     |_____|     |_____
  _____       _____       _____       __
B      |_____|     |_____|     |_____|

At any transition of any line, look at the other line to tell you
what direction you're going as follows:

	A		B		moving
	rising		high		left
	rising		low		right
	falling		high		right
	falling		low		left

	high		rising		right
	low		rising		left
	high		falling		left
	low		falling		right

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,
give short high pulses on each of A rising, A falling, B rising, B falling)
and then AND these each of these with the correct one of
A, inverted-A, B or inverted-B as in the table.

Then, Or together each of these 4 pulses for left and 4 for right
and feed that to a counter.

The pulses from the 1-shots have to be shorter than the pulse rate from
the highest rate of movement you expect from the mouse.

There are other ways to do the hardware; someone want to tell us
how the Amiga does it?
-- 
Steve Tell  Student, Duke University; Employee, Duke Tel-Com (summer only)
Former Chief Engineer, Cable 13 / Duke Union Community Television.
sgt@dukeac.ac.duke.edu;  {ihnp4, ulysses, et. al.}!mcnc!ecsgate!dukeac!sgt