- Joined: 28 Sep 1999
- Posts: 1197
|
More test results
 Posted: Wed Feb 06, 2002 4:12 am
|
I ran a few more tests today and came up with the following:
- If RAM at $C000-DFFF is disabled, the last opcode read by the Z80 is returned for every address within $C000-FFFF.
- For Phantasy Star, it's 8K of SRAM at $8000-9FFF is mirrored at $A000-BFFF.
I also have some details about the effects of enabling the cartridge slot and BIOS at the same time on an SMS 2. When this is done, $0000-7FFF returns *mostly* cartridge data but some values are corrupt, though I can't tell what the cause is (the exact bytes affected seems to be random). Even weirder is $8000-BFFF, if SRAM is not enabled it always returns cartridge data. If SRAM is enabled, each byte is the result of the BIOS data logically ANDed with the cartridge SRAM data. For example, if the BIOS values were F3 ED and SRAM was BD BD, the result is D3 C9.
Anyway, I doubt this is important to emulate, but for the sake of being complete I figure it is worth mentioning. It could be that the exact results are different depending on the cartridge (paging chip used, etc.) and the system it's being run on.
|
