Difference between revisions of "Sega Mega Drive/Quirks"
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GerbilSoft (talk | contribs) (→TAS instruction support: TAS works on registers, but not memory, on MD1 and MD2. Also, indicate that Gens and Gens/GS treat TAS to memory as no-op.) |
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* [[Ex-Mutants]] by Sega | * [[Ex-Mutants]] by Sega | ||
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Revision as of 16:00, 14 January 2011
This is a list of several MD hardware quirks that don't exactly fit in any other categories.
CLR on VDP data port
If the VDP is set to VRAM/CRAM/VSRAM Write, using the clr instruction on the VDP data port will result in a system crash:
- Emulators that implement this quirk: Unknown
TAS instruction support
The MC68000 has an instruction, TAS (test-and-set), that is used for synchronizing multiple MC68000s in a multi-CPU system. The TAS instruction uses a different bus cycle than other instructions, and is effectively treated as a no-op for memory writes by both the MD1 or MD2 hardware. However, the Majesco Genesis 3 does support TAS, which breaks a few games that incorrectly use the TAS instruction. (The TAS instruction ends up setting the high bit of the destination memory operand.)
- Emulators that implement TAS as no-op for memory access: Gens, Gens/GS, Gens/GS II, probably all others
- Emulators that implement TAS as write to memory: Unknown
Games that use the TAS instruction:
- Gargoyles by Buena Vista Interactive
- Ex-Mutants by Sega