> Of course you need to check all opcodes (IN's and
> OUT's will be very different),
According to the Gameboy technical specifications faq (to which Marat has
contributed) the CPU doesn't even know port I/O instructions. Here's what it
says about Z80 compatibility:
Processor
---------
The GameBoy uses a computer chip similar to an Intel 8080.
It contains all of the instructions of an 8080 except there
are no exchange instructions. In many ways the processor is
more similar to the Zilog Z80 processor. Compared to the
Z80, some instructions have been added and some have been
taken away.
The following are added instructions:
ADD SP,nn ;nn = signed byte
LDI (HL),A ;Write A to (HL) and increment HL
LDD (HL),A ;Write A to (HL) and decrement HL
LDI A,(HL) ;Write (HL) to A and increment HL
LDD A,(HL) ;Write (HL) to A and decrement HL
LD A,($FF00+nn)
LD A,($FF00+C)
LD ($FF00+nn),A
LD ($FF00+C),A
LD (nnnn),SP
LD HL,(SP+nn) ;nn = signed byte
STOP ;?
SWAP r ;Rotate register r by 4 bits
The following instructions have been removed:
Any command that uses the IX or IY registers.
All IN/OUT instructions.
All exchange instructions.
All commands prefixed by ED (except remapped RETI).
All conditional jumps/calls/rets on parity/overflow and sign flag.
The following instructions have different opcodes:
LD A,[nnnn]
LD [nnnn],A
RETI
Unfortunately, the document doesn't tell us which opcodes go with these
mnemonics, but at least it gives some valuable info about the hardware of
the GB. So pick up a copy of GBSPEC.TXT if you're interested. Or I could
mail it to you if ou like.
Pierre
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