6502-reasm

6502 disassembler and (re)assembler

Allows disassembling any sequence of bytes to a unique disassembly text, and reassembling the assembly text to the same bytes (fully roundtrippable). Includes support for illegal opcodes with multiple mneumonic aliases, and truncated operands represented by xx.

Intended for disassembling a ROM (or a part of a ROM), editing the assembly to patch it, and reassembling with the changes. See also: nes-game-genie and nes-file.

Example:

    const {disasm, formatDisasm, reasm} = require('6502-reasm');
 
    // returns an array, one element per instruction
    const lines = disasm([0x78, 0xd8, 0xa9, 0x10, 0x8d, 0x00, 0x20, 0xa2, 0xff, 0x9a, 0xad, 0x02, 0x20, 0x10, 0xfb, 0xad]);
 
    // returns a verbosely formatted text string, same as passed below
    const formattedDisassembly = formatDisasm(lines);
 
    // returns an array of bytes, identical as passed to disasm() above
    reasm(`\
00000000    78           SEI
00000001    d8           CLD
00000002    a9 10        LDA #$10
00000004    8d 00 20     STA $2000
00000007    a2 ff        LDX #$ff
00000009    9a           TXS
0000000a    ad 02 20     LDA $2002
0000000d    10 fb        BPL -5
0000000f    ad xx xx     LDA $xxxx
`);

License

MIT