I found that one in a WICO Trackball 72-4550 for the TANDY TRS-80 Color Computer. I guess it's reading 2-channel, 2-phased optical signals from the trackball, keeping track of the x and y coordinates and doing a 2-channel, at least 6-bit DA conversion using a discrete R/2R network. The output voltages (0 to 5V) go to the analog joystick input (x and y) of the Color Computer (where they are AD-converted by software using an internal 6-bit DAC and a comparator).

I never knew Motorola had been producing Intel derivatives.

Is there any chance to read out "the firmware" of that device?

I'm a totally newby to the 8052 (have been using 68HC11s in my projects).

Thanks for any hints,
Torsten