RCX Internals (Kekoa Proudfoot)

The canonical reverse-engineering of the RCX: serial/IR protocol, the byte-code interpreter, and the full opcode set. The reference that NQC, brickOS, leJOS and others built on.

What it documents

• RCX hardware: Hitachi H8 MCU, 32K external RAM, 3 motors / 3 sensors / IR serial port.
• The RCX IR protocol framing (header 55 FF 00, byte+complement pairs, checksum) and the toggle bit.
• Every opcode (alive/ping, set motor, play sound, poll value, download program/firmware, messages…).

Used alongside NQC · BrickCC and the crynwr LEGO Mindstorms Internals mirror (see Link directory).

Links

• Main: mralligator.com/rcx — the canonical live host (the Stanford original graphics.stanford.edu/~kekoa/rcx now 301-redirects here).
• Opcode reference: mralligator.com/rcx/opcodes.html.