Tiny 6502

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The smallest 6502 emulator in JS — ~300 lines, ~50 functions

BUILD GUIDE

1. Architecture Overview▼

The 6502 has a minimal register set: • A (Accumulator) - main math register • X, Y - index registers • SP - stack pointer ($0100-$01FF) • PC - 16-bit program counter • Status - N V - B D I Z C flags Memory: flat 64KB address space (0x0000-0xFFFF)

function create6502() {
  return {
    a: 0, x: 0, y: 0,
    sp: 0xFD, pc: 0x0600,
    n:0, v:0, b:0, d:0, i:0, z:0, c:0,
    mem: new Uint8Array(65536),
    cycles: 0
  };
}

2. Memory Access▶

3. Addressing Modes▶

4. ALU Operations▶

5. The Step Function▶

6. Stack Operations▶

REGISTERS

$00

$FD

253

$0600

1536

CYC

FLAGS:

SPEED:1000 Hz

MEMORY

ADDR	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
$0600
$0610
$0620
$0630
$0640
$0650
$0660
$0670

DISASSEMBLY

$0600BRK

$0601BRK

$0602BRK

$0603BRK

$0604BRK

$0605BRK

$0606BRK

$0607BRK

$0608BRK

$0609BRK

OUTPUT ($F001)

...

Built with ❤️ and 6502 nostalgiaThe 6502 powered the Apple II, NES, and Commodore 64Remix on Berrry