) A unidirectional protocol for controlling theatrical lights and special effects machines. DMX512 was developed by the Entertainment Services and Technology Association (ESTA) in the late 1990s. Providing 512 channels per link, DMX512 is based on RS-485 electrical signaling. Up to 512 target devices are daisy chained together via "In" and "Out" sockets, and cables use 5-pin XLR connectors. Via gateways and the "Streaming ACN" protocol, DMX data can ride over IP and Ethernet. The latest version of DMX512 is officially USITT DMX512-A (2008). See XLR connector
Remote Device Management (RDM)
Developed in 2005, RDM is an enhancement to DMX512 that provides two-way transmission between controller and RDM-compatible devices over the same lines. Because there is communications back to the controller, RDM units can report their identity and features to the lighting engineer. In addition, rather than climbing a ladder to a light in order to physically change its address, RDM is used to change address from the console. However, legacy DMX products that assume all packets are DMX without checking start codes can react inappropriately when RDM signals are transmitted.
DMX/RDM Theater Consoles
ETC is a major provider of DMX/RDM equipment, including consoles, light fixtures, rigging and networking. (Image courtesy of ETC, www.etcconnect.com)