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From Sonic Retro

The "GB-Z80" is Nintendo's rendition of Zilog's Z80 processor core used in the Game Boy. Compared to a vanilla Z80, some instructions have been added, and some removed to better suit the hardware.

Added instructions include:

 STOP
 LD  (HLI),A
 LD  (HLD),A
 LD  A,(HLI)
 LD  A,(HLD)
 LD  ($FF00+nn),A
 LD  ($FF00+C),A
 LD  A,($FF00+nn)
 LD  A,($FF00+C)
 LD  (nnnn),SP
 LD  HL,SP+nn
 ADD  SP,nn
 SWAP r

Removed instructions include:

• Anything utilizing the IX or IY registers
• Exchange instructions.
• Conditional jumps/calls/rets on parity/overflow and sign flag.
• No IN/OUT instructions
• Commands prefixed with ED (not remapped RETI).

Reassigned Opcodes:

 LD  A,[nnnn]
 LD  [nnnn],A
 RETI

External Links

More information can be found in The GBDevrs scene.