DMX512A

DMX512A is a digital communication protocol used in entertainment lighting to control fixtures. It is a revision of the DMX512 standard, intended to clarify and standardize timing, electrical characteristics, and data framing to improve interoperability among controllers and devices.

The protocol operates on a unidirectional, master-to-slave data stream over RS-485. A DMX512A frame carries up to 512 channels (slots), each one byte. The frame begins with a break (a low level on the line), followed by a mark-after-break, then the channel data. The first data slot controls channel 1, with subsequent slots mapping to channels 2 through 512. Data is typically transmitted continuously at regular intervals by the controller.

Wiring and connectors utilize RS-485 signaling and commonly employ 5-pin XLR connectors, with devices daisy-chained in a line. Proper termination at the far end, typically with a 120-ohm resistor, helps prevent reflections, and biasing helps maintain a known line state when the data stream is idle.

Compatibility and scope: DMX512A remains broadly compatible with devices implementing the original DMX512, while providing clarified timing and electrical definitions to improve interoperability. It is widely used in stage lighting, film and theater facilities, concerts, and architectural lighting installations.

Related standards: DMX512A is frequently used alongside Remote Device Management (RDM), which operates on the same physical layer and adds bidirectional communication for device management, discovery, and configuration; RDM requires compatible equipment and software.