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6502 in your browser

Write 6502 assembly, hit Run, and watch it execute. The CPU is a from-scratch C++ emulator compiled to WebAssembly; the assembler is TypeScript running right here on the page. Nothing leaves your browser.

    Console $FF00 out · $FF01/$FF02 in

    Registers
    A
    00
    X
    00
    Y
    00
    SP
    FD
    PC
    0000
    Cycles
    0
    NV-BDIZC
    Memory
    Assembly listing & symbols
    Quick reference
    Syntax
    ; comment
ORG $0600        ; where code goes (default $0200)
LIMIT = 10       ; constant
loop:  LDA #LIMIT
       STA $10,X
       BNE loop
.byte 1, "hi", 0
.word $1234
.fill 4, $FF
    Numbers: $FF%101042'A'. Operators:+ - * / & | ^ << >>, plus <label / >labelfor the low / high byte. Execution stops when an instruction jumps to itself (JMP *).
    Devices
    AddressWhat
    $FF00Write a byte: shows in the console
    $FF01Read: bit 0 set if a key is waiting
    $FF02Read: next key (0 if none)
    $FF10–11Timer reload value (lo, hi)
    $FF12Timer control: bit 0 enable, bit 1 periodic
    $FF13Timer status; any write acknowledges the IRQ
    The IRQ vector lives at $FFFE: put .word handler there under anORG $FFFE. The Timer example does exactly this.