Gameboy

The full GB-Z80 instruction-set is implemented with a few modifications to the original Zilog syntax. This is due to a Bison problem but in my opinion the syntax is better than the original one.

Instructions

• ADC
• ADD
• AND
• BIT
• CALL
• CCF
• CP
• CPL
• DAA
• DEC
• DI
• EI
• EX
• HALT
• INC
• JP
• JR
• LD
• LDD
• LDI
• LDH/LDIO (see note below)
• NOP
• OR
• POP
• PUSH
• RES
• RET
• RETI
• RL
• RLA
• RLC
• RLCA
• RR
• RRA
• RRC
• RRCA
• RST
• SBC
• SCF
• SET
• SLA
• SRA
• SRL
• STOP
• SUB
• SWAP
• XOR

Note that you can use both

    OR   A,B
    OR   B

Addressingmodes

Indirect addressing has been changed to [ ] instead of ( ):

• A
• B
• C
• D
• E
• H
• L
• AF
• BC
• DE
• HL
• SP
• [BC]
• [DE]
• [HL]
• [HL-]/[HLI]
• [HL+]/[HLD]
• [SP]
• n8 (8 bit expression)
• n16 (16 bit expression)
• n3 (3 bit CONSTANT expression)
• [n16]/[$FF00+n8]
• [$FF00+C]/[C]

The assembler will intelligently decide between [n16] and [$FF00+n8] in the LD instruction. Note however that if you use any constant symbols in the expression they had better be defined before the instruction or your symbol-table may become mangled. Also worth noting is that it will only ever select the short $FF00 mode when you use constant symbols. NOT if you use symbols defined in a HRAM section. As this defies the whole point of implementing the HRAM sectiontype I've added the LDIO mnemonic. It works like the LD instruction but it will ALWAYS generate the $FF00+ form and it will also automatically logically AND the expression with $FF if it is relocatable. Which is what you want. Trust me ;)

Conditioncodes

• C
• NC
• Z
• NZ

Last updated 20 July 1997 by Carsten Sorensen