[Coco] GIME behavior

[Darren A]

Does anyone know if the GIME drives the CPU data bus when you read
from a write-only register?

I have a hardware project which stores writes to $FF90 in a separate
latch. I had figured I could also use address $FF90 to read the latch
since this is a write-only register in the GIME. No such luck.

I know my hardware is working because when connected to a CoCo 1 or 2
I can read and write $FF90 as if it were RAM.  On a CoCo 3 the latch
does record writes (verified with LEDs), but trying to read it back
does not work.  The only explanation I can think of is that the GIME
does drive the data bus on a read of $FF90 even though it provides no
useful data.

Darren