MCD manual claiming issues with PSG access from Z80

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Ralakimus
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MCD manual claiming issues with PSG access from Z80

Post by Ralakimus » Wed Oct 26, 2022 7:53 pm

This is really confusing me. Would anyone here happen to know why the MCD manual states that the Z80 cannot access the PSG, let alone apparently anything related to the Genesis 68000 when the MCD is running?

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The only thing I can think of is some potential edge case due to the PSG being on the 68000 bus, but I feel that would also apply to just the Genesis in general, not just MCD? Regardless, I haven't seen any real evidence of the manual's claim so far.

Chilly Willy
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Re: MCD manual claiming issues with PSG access from Z80

Post by Chilly Willy » Wed Oct 26, 2022 10:57 pm

That bit about not accessing areas of the 68000 is referring to the CD HW. It goes with the first two - don't access ANY part of the CD, be it ram or hardware with the Z80. The CD IO is probably only expecting standard 68000 accesses, not the byte-wide, not quite 68K, Z80 accesses. They actually put some work into the 32X on this front - you can actually access most of the 32X hardware with the Z80.

Not sure what the warning about the PSG is. The PSG is inside the VDP, and the MD allows the Z80 to access it as you can see with most music players for MD games. I don't see why the CD would have a problem with that.

Ralakimus
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Re: MCD manual claiming issues with PSG access from Z80

Post by Ralakimus » Thu Oct 27, 2022 5:13 pm

Thanks. Damn MCD manual's weird wording/mistranslations...

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