DMX512 protocol

DMX512 is a digital communication standard used to control stage lighting and related equipment such as dimmers, colour changers, moving lights, and fog machines. It was developed to give lighting consoles a common, manufacturer-independent way to send level commands to fixtures, replacing the incompatible analogue control schemes that came before it. A single DMX line carries up to 512 control channels, and each channel conveys a value that typically sets the intensity of a dimmer or the position of a parameter on an intelligent fixture.

Electrically, DMX512 is built on the RS-485 serial standard, which uses a balanced, differential pair of wires to carry data reliably over long cable runs and in the electrically noisy environment of a venue. Devices are wired in a daisy chain from one fixture to the next, and the far end of the line is terminated to prevent signal reflections. The controller continuously streams packets, each made up of a start code followed by the values for the channels, so fixtures receive frequent updates to their settings.

Each receiving device is assigned a starting channel address, and it reads the block of channel values beginning at that address, ignoring the rest. A simple dimmer pack might use one channel per circuit, while a moving light may consume many channels for pan, tilt, colour, and other functions. Because the protocol only carries control data in one direction and includes no error correction, careful cabling, proper termination, and respecting the limit on devices per line are important for dependable operation.

Frequently asked questions

How many channels does DMX512 support?

A single DMX512 line carries up to 512 channels, each holding one control value. Fixtures with many functions use several channels, so a large rig may need more than one line.

What wiring does DMX512 use?

It uses the RS-485 differential serial standard, with devices connected in a daisy chain and the last device terminated to suppress signal reflections.

What is a DMX address?

Each fixture is given a starting channel number and reads the block of channel values beginning there, which lets several devices share one line without conflicting.