Hi
>>>Because R800 executing DJNZ & JR
>>>instruction another way for calculating destination address
>>
>>I don't think so. R800 can execute all Z80 code in the same way as a real
>>Z80 does.
>
>Then no sense to put 2 processors
>I take it from Z80 and R800 Assembly/Machine Language Op-code Tables
The R800 isn't totally Z80 compatible. For instance, the undocumented
instruction SLL doesn't exist on a R800. It's because R800 is derived from
Z800 family, not Z80. I haven't tested the behaviour of the 30h-37h (SLL in
Z80) opcodes on R800 thoroughly, but I do know they are not the same.
Supposedly they are some sort of test instruction...
So, since the SLL instruction is often used in MSX programs, the original
Z80 SHOULD be there (also for timing purposes, like Shevek already stated).
Greetz,
Patriek
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