I did some more TMC0430 tests: http://www.seanriddle.com/grom.html
I bought a TI 99/4A DOS Manager 2 cart and dumped the 2 GROMs. Contrary to what I originally thought, they appear to operate identically to the GROMs in Milton.
First of all, the Milton GROMs are only 6K, as seen on the die shot. When you keep reading past the end, the output looks like normal data; it's not all 00 or FF, isn't random, and isn't a duplicate of previous data. So I thought I was getting 8K.
Addresses are written and read MSB first. One source (http://www.unige.ch/medecine/nouspikel/ti99/groms.htm
) says LSB first, but another (https://archive.org/details/tibook_hardware-manual-for-the-texas-instruments-994a
) says MSB first.
But both sources say pin 1 is D7 and pin 8 is D0, while my tests show pin 1 is the lsb and pin 8 is the msb.
Let me know if anyone has any other tests they want me to run.
D'oh - I see now that the TI 99/4A convention is that D0 is the msb and D7 is the lsb. So everything I've seen is consistent with the hardware manual I linked above.