How DMX Works
Understanding the technical aspects of DMX protocol and signal transmission.
DMX512 protocol data structure and timing
The DMX Protocol
DMX512 is an asynchronous serial protocol that transmits digital data between controllers and receiving devices. The protocol is based on the EIA-485 (previously RS-485) standard, using differential signaling over twisted-pair cable to provide noise immunity in electrically noisy environments like concert venues and theaters.
Each DMX data packet begins with a "break" signal, followed by a "mark after break" (MAB), and then a start code. After this header, up to 512 channels of 8-bit data (values 0-255) are transmitted sequentially. This entire packet is typically sent 44 times per second, providing smooth real-time control.
DMX Universes and Channels
A single DMX universe consists of 512 channels, each capable of transmitting a value between 0 and 255. Different lighting fixtures require different numbers of channels to control their various functions:
- A simple dimmer might use just 1 channel (intensity)
- An RGB LED fixture typically uses 3 channels (red, green, blue)
- A moving head light might use 16+ channels (pan, tilt, color, gobo, focus, etc.)
For larger installations requiring more than 512 channels, multiple DMX universes can be used, each with its own data line.
Visual representation of a DMX universe with 512 channels
DMX Hardware Components
A typical DMX system consists of several key components:
- Controller: The source of DMX signals (lighting console, computer with DMX interface, etc.)
- Fixtures: Devices that receive DMX signals (lights, fog machines, etc.)
- Cables: Specialized DMX cables with proper impedance (typically 120Ω)
- Splitters/Repeaters: Devices that boost signals for long runs or multiple branches
- Terminators: 120Ω resistors placed at the end of DMX lines to prevent signal reflection
Common DMX hardware components and connector types
Channel Control and Values
Each DMX channel can have a value from 0 to 255 (8-bit resolution), which controls a specific function of a fixture. For example:
- For a dimmer, 0 might be off and 255 might be full brightness
- For a color wheel, different ranges might select different colors (0-10 for white, 11-20 for red, etc.)
- For a moving head's pan function, 0-255 might represent a 540° range of motion
Fixtures come with DMX charts that explain which channel controls which function and what the different values do. Programming a DMX show involves setting these channel values at specific times to create the desired lighting effects.
How DMX channel values control different fixture parameters
Next Steps in Learning DMX
Now that you understand how DMX works, explore these related topics: