Just a quick reference for those making infinite-something Game Genie codes for retro consoles.

General tools i use regularly:

• ucon64 (Game Genie encoder/decoder, rom patcher, and more)
• qalc (cmdline calculator)
• Retroarch (decent GUI to look for memory addesses)

suggested emus with breakpoints and a debugger:

• NES: fceux
• SNES: bsnes-plus
• SMD: Mednafen (very ugly UI, but works), MAME
• SMS, GG: Gearsystem
• PCE: Mednafen (very ugly UI, but works), MAME
• GB: BGB
• GBA: no$gba debug version

opcodes references:

• 6502 (NES, SNES, PCE)
• m68k (SMD)
• Z80 (MSX, GB, SMS, GG)

common ASM opcode replacements:

• Z80 (original guide):
  • 90, 91, 92, 93, 94, 95 -> 00 (DEC->NOP)
  • EA -> FA (LD reg2mem -> LD mem2reg)
  • …
• 6502 (original list posted here):
  • CE -> AD (DEC->LDA)
    DE -> BD (DEC->LDA)
    C6 -> A5 (DEC->LDA)
    85 -> A5
    D6 -> B5
    95 -> B5
    8D -> AD
    9D -> BD (STA->LDA)
    DE -> BD
    91 -> B1
    99 -> BE
    EA (NOP)
• m68K:
  • most used opcodes are 6002 and 6004 (= Branch 2 or 4 bytes).
  • to skip a single instruction, a single NOP= 4E71 will do.

general tricks:

• to NOP multiple instructions, you can use an unconditional branch instruction, or, if near a “RET” (=routine return) you can just call RET before.

Some codes i’ve made can be found here.

P.N.: i am not taking cheat requests currently, so please do not ask in the comments.