DMX is a protocol used in stage and show equipment. This includes lighting, fog machines, motors, etc. The protocol consists of a Controller that sends out commands, and receiver such as theater lights that receive these commands. The DMX protocol is usually unidirectional, but can be a bidirectional protocol in either Half or Full-Duplex modes. An example of a Half-Duplex mode is the RDM (Remote Device Management) protocol that sits on DMX512A. The Controller transmits commands and the receiver receives them. There are no error conditions or re-transmit mechanisms.
DMX, or DMX512A as it is known, consists of a “Universe” of 512 channels. This means that one Controller can output up to 512 bytes on a single DMX link. Each piece of equipment on the line is programmed to listen to a consecutive sequence of one or more of these bytes.
For example, a fog machine connected to one of the universes may be programmed to receive one byte, starting at byte number 10, and a lighting unit may be programmed to receive four bytes starting at byte number 22.