Re: Wondering about an Apple //c Mouse

[petri@mmt.bme.hu (Petri Andras)]

In article <20040511202856.13561.00000413@mb-m27.aol.com>, mjmahon@aol.com (Michael J. Mahon) writes:
> Simon wrote:
> 
> >Rob Steinmetz <rsteinmetz@-no-mindspring.com> wrote:
> >
> >> Did Apple ever manufacture a mouse specifically for the Apple 
> >> //c or //c+?
> >> 
> >> I know the original Apple Mouse will work, I was just wondering 
> >> if one was ever made which matched the Arctic White color of the 
> >> //c. Similar to the 5 1/4" disk drive with a latch which matched 
> >> the //c which was available.
> >
> >Actually, not all mice work with the //c, though I don't recall
> >specifically what the differences are, I know that I've had mice that
> >work on a IIe but not a //c and also some that work on a Mac Plus, but
> >not on a IIe... or something like that.
> 
> Yes--I suspect that the problem arose because of the //c using
> the joystick connector for the mouse.  It's a neat trick, but a
> few wires are bound to be different, and perhaps all mice didn't
> ignore the ones that were not supposed to matter.

I've made some experiments a few months ago, when I got an Apple IIc with GEOS
on floppies but without mouse. I tried to convert an Amiga mouse, as I had a
surplus one and it seemed to be electrically compatible with just a different
connector and pinout. I made a simple pinout converter from two DB9M connectors
and some wire.

It didn't work. The mouse button was OK, but the cursor always wondered to
one direction (to the right or down) wherever I tried to move the mouse.

A bit later I could persuade a local Apple dealer to lend me the original
mouse of an Apple IIc (from their Apple hardware museum ;-). It was a "white
body, beige-grey button" type thing. I've opened its case - without them
knowing, of course ;-) - and checked the PCB. Then I could find the cause of
the problem: Amiga and Apple IIc mice are NOT electrically compatible!

\begin{boring_technical_stuff}

The root cause is that the Apple IIc uses the *analogue* joystick inputs for
processing the *digital* quadrature signals coming from the mouse. (It is a
rather weird idea from an engineer's point of view - in joysticks, a pair of
variable resistors is connected to these inputs that control timer circuits
so that the length of the timers is proportional to the X/Y position of the
stick. Mice, however, produce a series of quadrature impulses so that the
frequency of the impulses is proportional to the speed of mouse movement.)

The mouse port of the Amiga computers - and supposedly also ancient Macs,
and maybe Apple IIe's and Apple II mouse cards - expects the quadrature
signals to come from CMOS outputs; however, Apple IIc's analogue joystick
inputs expect them from TTL outputs.

As both TTL ans CMOS outputs can drive CMOS inputs but TTL inputs cannot be
driven properly by a CMOS output, it is quite reasonable that some of the
MacPlus/IIe mice (with TTL ICs in them) work with the IIc while others
(with CMOS ICs) do not.

\end{boring_technical_stuff}

I checked this theory by making a simple CMOS->TTL signal converter (with
which I could attach my Amiga mouse to the IIc) and cross-checked it by
wiring an even simpler pinout converter (with which I could connect the
Apple IIc mouse to my Amiga, even if it did not make any sense ;).


Regards,

Andras Petri