Date   : Wed, 25 Aug 1999 20:21:10 +0100
From   : Iain Williamson <Iain@...>
Subject: Re: Mouse on the BBC

In message <4936C53F7B%Iain@...>
          Iain Williamson <Iain@...> wrote:

> In message <1EowVaAUCew3EwDX@...>
>           Stuart William McConnachie <stuart@...> wrote:

> > In message <49363B1E5D%Iain@...>, Iain Williamson
> > <Iain@...> writes
> > >> Does any of you guys know how to connect a standard PC-mouse to the
> > >> user-port in order to use the AMX-software?? (if at all possible?)

> [snip - AMX mouse]

> > >On the other hand if it plugs into the user port, it must have been a
> > >digital device; perhaps similar to a modern PS2 mouse.

> > Although digital in nature, the AMX mouse was a very low level device,
> > only signalling the BBC with an interrupt when the mouse moved (one
> > unit) and the direction it moved in.  It was the responsibility of the
> > BBC to count the number of movements in each direction and thus the
> > total distance travelled.  I believe the PC mouse interface is much more
> > complicated, with the PC mouse being a more intelligent, programmable,
> > device with a serial interface.

> I believe the PS2 interface is similar; it sends simple framed serial data
> to the computer consisting of change in X, change in Y, button state (not
> neccessarily in that order). I can't remember if it does this constantly,
> or only when moved.

I've had a bit of a braino there. A quadrature mouse _is_ digital; the
whole working of a mouse are digital; the optical switches are either on
or off. It's just not a serial communication.

>From what other people have said, it looks very like an AMX mouse is a
style of quadrature mouse (inside should just be a set of buffers connected
to the optical switches).

You will not be able to wire a PS2 mouse to a port expecting quadrature
signals. People have said in other forums that many old PS2 mice can be
butchered and made to work, but most modern ones make this very very
hard. Some modern systems still use quadrature mice, you see (like the
one in front of me).

Stuart Tyrrell does make a box to adapt PS2 signals to quadrature. It's
not simple, and therefore not cheap - but I understand it to be very
well built. He's a very helpful chap IMO and has a BBC background, so
may be able to help on this directly. Try http://www.stdevel.demon.co.uk/
(or mail him on stuart@... )

I hope all that makes things a bit clearer.

-- 
  /""\          Iain Williamson
 C  oo      Computer systems engineer
 _(  ^)
/    ~\