RCX

The RCX is the flagship MINDSTORMS brick (Robotics Invention System, 1998–2001), built around a Hitachi H8 microcontroller with 3 motor outputs, 3 sensor inputs, an LCD, and a speaker. It is programmed and commanded over a two-way infrared link.

Optical input / output

• Two-way infrared via the IR tower — a real serial link, see RCX IR protocol. This carries firmware, programs, direct commands and messages.
• Light sensor input (reflected/ambient brightness) — same physics as VLL, used for sensing.
• RCX↔RCX messages over IR let bricks talk to each other.

Firmware

A small OS must be flashed first (firm0309/0328/0332.lgo; Dick Swan's fast0612.lgo is 50–100× faster). Upload with nqc -firmware firm0332.lgo. See pbrick.info.

How to control it today

• NQC · BrickCC — the classic toolchain.
• LegoRcxPy — Python over a serial IR tower (DB9).
• BrickLogo — modern Logo REPL with RCX serial/IR support.
• Official period software: RIS · RCX Code (consumer drag-blocks) · ROBOLAB (LabVIEW, education).
• Replacement firmwares (run native code on the H8): legOS · brickOS (C/C++) · pbForth (Forth) · leJOS (Java).
• A USB IR tower (or serial tower) is required; the same tower can flash VLL to a Micro Scout.

Full command set: RCX opcode table.

An RCX can itself emit VLL by flashing a LEGO 9V Light brick (via RCX) on an output port — see rcxvll.nqh (pbrick).

Links

• Sets: 9719 RIS 1.0 · 9747 RIS 1.5 · 3804 RIS 2.0 — see Sets & bricks index.
• IR tower: 9713 (serial) / 9783 (USB).
• Spec: RCX Internals (Kekoa Proudfoot). macOS: mindstorms-rcx-osx-tools. Tower control: InfraredBrickTower.