DMX512

DMX512 is a standard for digital communications networks used to control stage lighting and effects. It was first published in 1986 by the USITT (United States Institute for Theatre Technology) and has become the de facto protocol for theatrical lighting control. The standard defines the electrical characteristics, the frame structure for data, and the recommended connectors and cables. DMX512 is a unidirectional, serial protocol that transmits from a lighting controller to devices such as dimmers, intelligent fixtures, and effect units.

The physical layer is based on RS-485 differential signaling at a data rate of about 250 kbit/s. A typical DMX link uses a 5-pin XLR connector, though 3-pin variants are common in some systems. The network is designed as a daisy-chained chain and may be terminated with a 120-ohm resistor at the far end to prevent reflections. The practical length of a DMX cable is limited by the specification, often cited as up to roughly 500 meters with proper termination and cabling.

A DMX universe consists of 512 channels. Each channel carries an 8-bit value (0–255) that controls a parameter on a device, such as a dimmer level or fixture attribute. A device may consume multiple consecutive channels, so the number of devices per chain depends on their channel requirements. The data frame begins with a break (a dominant level longer than about 88 microseconds), followed by a mark-after-break, then a start code (usually 0x00) and up to 512 data bytes.

DMX512 is widely used in entertainment lighting and is often extended with multi-universe systems via splitters or modern controllers. For two-way device management, the related protocol RDM provides bidirectional communication over the same DMX line.