Some success this morning working with the TPU. I first wrote a routine to load the TPU. Used the '97 flash routine with no mods. Seemed to load OK (no smoke) so I added a timer driven read/display of the VATS register at $146A. This also worked. I looped the EGR pwm back to the VATS input. I set the EGR for a 50HZ rep rate and a square wave using the constant $7A80 to configure the pwm at $1808. Reading back and subtracting last value gave me the constant I expected.

I will next try to mod the microcode to see if I can place the output at a different place.

Small steps...

-Tom