From: graham@venus.iucf.indiana.edu (JIM GRAHAM)
Subject: Re: Serial mouse on an amiga
Followup-To: comp.sys.amiga.hardware
News-Software: VAX/VMS VNEWS 1.3-4   
Reply-To: graham@venus.iucf.indiana.edu
Organization: Somewhere in Bloomington, Indiana
Distribution:  world
Date: 28 JUL 92 08:57:12    

In article <4095@winnie.fit.edu>, ree88132@zach.fit.edu (Keith Ledig) writes...
> 
> 
>I am trying to interface an IBM serial mouse to an amiga computer
>and I need a little info.  I know the pinouts of the Serial port
>(DB9) and the amiga mouse port(quadrature signal type), but I need
>to know what the data looks like coming out of the serial mouse.
>Is the send data and signal groung all I am concerned with, or
>do I need to concern myself with the signals like request to send, 
>data set ready, etc.  Also, what type of circuit do I need?
>I hooked up the mouse to my serial port while running a terminal
>prg and I say some characters with regularity at 2400 baud
>(i.e. left button click I got a certain ascii character every time)
> 
>I am guessing here but I think I need to build a circuit that will
>take the 8 bits off the send data and (demultiplex???) it out to
>8 controll lines.  What I think is that maybe the first bit is a 1
>if the mouse is traveling upward, second bit downward, etc.  Maybe the
>5th bit is left mouse button.  Do I need flip-flops to hold the signal?
>My above theory would make sense since it allows for you to hold
>the mouse button and drag in any direction.  Am I close?  :-)
> 
>The amiga needs the raw quadrature signals. xa, xb, ya, yb, left button,
>right button, signal ground.  The IBM mouse is a 2 button type.
>(and amiga can make use of 3 button types as well)  I know about the
>fact that IBM serial mice require 12V (RS232) and amiga mouse port
>provides only 5V (and at a low 50 mA to boot!).  I will probably
>provide an external power supply initially.
> 
>This is for my own satisfaction.  I enjoy hardware hacking.  I know
>I can get an Amiga mouse for almost the same price.  Did the inventors
>of the DKB talker say that too?  :-)

I'm not sure if this'll answer your question, but here goes.

I am presently using a Mouse Systems trackball on my A500.

It too is basically the same, operationally as a serial mouse.

What I did was the following....

1.) Trace the circuit, making a schematic diagram (reverse engineering
    at its best :-).

2.) There is usually an IC that converts the mouse mechanisms
    quadrature signals to a serial rs232 bit stream.

3.) Disconnect the serial output from this IC.
4.) Find the actual quadrature inputs to the IC, and connect them
    to the appropriate connector pins for your amiga mouse port.

It is also probably necessary (at least it was in my case) to find
the trace on the pc board that supplies the dc voltage (12 volts
or so) to the quadrature transistors.

You'll have to disconnect both the positive and negative voltages from
these transistors (there will be 4, 2 of which are NPN, and 2 PNP).

Then you'll have to connect the +/- connections to +5V and GND.

If you're familiar with properly biasing a simple switching transistor,
then this should be a piece of cake for you.

It may help you immensely (it did in my case) to use an oscilloscope
to find the actual quadrature signals.  You may be lucky enough to
get a serial mouse whose quadrature signals are already at TTL levels,
but I doubt it.

If not, it's easier and just as cheap (at least now) to go out and
purchase a regular _Amiga_ mouse. :-)

At the time that I did this hack, it was cheaper to purchase an
IBM compatible serial trackball.  That is no longer the case.

Jim Graham 

        -> ->Disclaimer: I do not speak for my company. <- <-
                          Neither do they speak for me.
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