[Coco] The RAT Graphics Mouse

[tim lindner]

Michael Crawford recently sent me a CoCo mouse to reverse engineer. It
was sold with Diecom's The RAT Graphics package:

http://home.netcom.com/~tlindner/TheRat.html

It appears to an OEM PC mouse from about the 1987 era. The quadrature
encoding wheels have been hacked to encoding an analog signal sent
directly to the CoCo. The four values it cycles thru are:

   15, 24, 42, 15

The faster you move the mouse, the faster the numbers cycle.

This is a cool way to handle mouse I/O, becuase no expensive analog to
digital chip is needed, but it is more complicated to create a software
driver for this kind of mouse.

Since the mouse only gives you the horizontal and vertical components of
the speed and direction (a vector) you have to calculate the position of
the pointer in the CPU. But you do get infinate resolution. That's a
bonus!

-- 
tim lindner
tlindner at ix.netcom.com                                        Bright