UTTORI ASM · IN DEVELOPMENT

Undocumented 6502X

Use undocumented 6502x in 6502-family and NES projects, with syntax and limits.

arch 6502x also accepts ca65's undocumented mnemonic set. Common alternate spellings such as ISB/ISC, KIL/JAM, and SBX/AXS are source aliases. Duplicate opcode encodings remain visible in the exported 256-entry decode table, while ordinary source assembly chooses one canonical encoding.

Unstable instructions (ANE immediate, LAX immediate, SHA/SHX/SHY/TAS indexed stores) are deliberately accepted and tagged unstable-undocumented. The encoder promises a byte value, not stable behavior on every NMOS die revision.

arch 6502x
slo $20
isb $21
kil