Reading from write-only TIA registers
What do you get when you read from the write-only TIA registers, like GRP0, HMP0, etc.?
I know you don't get the value that's actually in the registers, but what do you get?
I was messing around with PCAE testing some of this but I'm not sure if that emulator correctly emulates this stuff - anybody know? - so I thought I'd ask you smart folk
For example, in PCAE, after this:
lda #$FF
sta GRP0
lda GRP0
A is zero.
Trying to follow the trace file in z26...
And after this code:
lda #$FE
sta GRP0
lda GRP0
A holds $1B, which is the address of GRP0, when run by z26. Which seems odd.