Date   : Wed, 11 Jun 1986 22:08:54 GMT
From   : Dave Haynie <daveh%cbmvax.cbm.UUCP@seismo.css.gov>
Subject: Re: Commodore 128 Mouse Interface

> 
> I plugged the C-128 mouse into the rig of my own design and manufacture
> for a Z-100.   I also plugged a regular joystick into the mouse program.
> I did not put the mouse on a scope, but the results are conclusive:
> The C-128 is not a real mouse, but is an inverted tracball (probably
> using the same IC that is in the tracball too).  It does not yield any
> stepping increments or my custom software would have been able to detect
> it.    A REAL mouse costs money to make, the C-128 is cheap.
> The Commodore man is full of it, you can check it out for yourself.
> 
> Cheers,
> Gern
> -------

Maybe you should have scoped it out. The Commodore Mouse is in some 
ways a real mouse and in some ways not, of course depending upon what 
you consider a "real" mouse. The mouse workings are very cheap in most 
everyone's mouse; they simply consist of two circular wheels 
alternately transparent and opaque, which cause two phototransistors to 
pluse in proportion to the velocity at which the mouse moves. The 
expensive part comes in the mouse interface, which generally transmits 
some good and meaningful velocity information in a form that the 
computer can accept. Up to this point, a trackball does something very 
similar, and the two are really interchangable.

Now the interface on the CBM mouse is a custom microprocessor that sits 
out in the mouse and watches the motion of the vanes. It will pulse a 
four bit digital TTL level signal which corresponds to the 4 bits of 
joystick information all Commodore consumer type computers accept. Thus 
it is compatible with joystick software, at least to a degree. The main 
problem is that the pulsed digital lines can easily get saturated when 
moving the mouse; this seems to happen even at reasonably slow speeds. 
Also, even a program written specifically to read the mouse is going to 
look sloppy as compared to the same thing with a standard quadrature 
mouse, the digital pulsing takes lots of processor time to scan 
correctly, and it still doesn't convey the same resolution of 
information available in the mouse that you're thinking of.

Most arcade-style trackballs take an even simpler route, and don't 
pulse the digital output at all; they look just like digital joysticks. 
That's what you get for buying a Commodore/Atari/ETC COMPATIBLE 
trackball. There are also trackballs that generate a quadrature output 
compatible with the mouse output on an Amiga or MAC machine.

The bottom line is that the current Commodore Mouse, as intended for 
C64 and C128 style computers, is a compromise between full mouse 
functionality and compatibility with software that's out there.

-- 
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Dave Haynie    {caip,ihnp4,allegra,seismo}!cbmvax!daveh

 These opinions are my own, though for a small fee they be yours too.
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