The DMX protocol, Digital Multiplex (DMX), is a serial control protocol for lighting technology used in lighting management. The DMX concept was designed for stage technology, but it is increasingly used in intelligent lighting of homes, office buildings and halls. The DMX protocol can be used to control lighting effects with color temperature and brightness programmed.
The DMX protocol is based on the RS-485 serial interface with balanced transmission. The connector prescribed is the five- pin XLR connector used in audio technology. Three of the five connector contacts (1, 2, 3) are for ground, the DMX cold signal for negative level and the DMX hot signal for positive level. The signal levels can be between +/- 1.5 V and +/- 5.5 V with a high common mode voltage. Due to the balanced signals, which are transmitted in opposite phase with identical level, interfering signals are compensated.
As far as data transmission is concerned, parameters are transmitted with a frame, which in DMX512 consists of 512 slots that can be used to control 512 channels, each of which comprises eight bits, plus a start bit and two stop bits. This allows 256 levels to be transmitted. Each slot is used to control a light source, color changer, strobe or dimmer. The bits have a duration of 4 µs.