DMX, acronym for Digital Multiplex, is a communication protocol for lighting control, developed as digital transmission method for data between controllers and controlled devices, including dimmers and related equipment. This standard is oriented to guarantee interoperability both for communication and mechanics among controllers from different manufacturers.

Origin and evolution

USITT (United States Institute of Theatre Technology) develops and promotes a wide range of technologic standards for theatric and show-business industry. Among those, in 1986 USITT has developed DMX512 as standard protocol for lighting control. In 1988 USITT has transferred the maintenance of the protocol to ESTA (Entertainment Services and Technology Association), a non-lucrative category association representing the entertainment industry of technology.

In 2004, ANSI (American National Standards Institute) approved the DMX512 standard and subsequently other related rules.

The standard is constantly reviewed and updated along with the progress of technology: the devices which are compliant to the 2008 release are marked with the DMX512-A notation in order to distinguish them from those developed according to the previous releases. Although developed and acknowledged in the US only, DMX512 is spread worldwide.

Standard charateristics

DMX512 is based on a serial asynchronous 8-bit protocol composed by an uncompressed byte stream which is produced by a standard universal asynchronous receiver-transmitter (UART); the ‘512’ suffix refers to the maximum number of addresses configurable in a DMX field, called “DMX universe”.

If two DMX devices connected to a universe have the same address, they are controlled in parallel.

The transmission medium is normally (although not exclusively) a twin couple conductor, with each couple acting as data connection. If necessary, repeaters can be used in order to overcome the length limit of a DMX network.

The connection of the devices is carried out with 5-pole XLR connectors or by physically connect the terminal blocks. The data on the primary connection is sent in packets up to 513 slots; the first slot is composed by a starting code which defines the information on the subsequent slots of the packet. Interoperability among standard compliant devices is mostly due to the use of the NULL START code by the transmitting devices.

Fields of application

DMX512 is not a general-purpose lighting standard: both device designers and standard users use DMX512 for a limited range of applications, mostly for entertainment industry when a central direction console needs to control the scenic lighting composed by a big number of lights and effects, and for the scenic illumination of historic buildings.

Other standards are more suitable for other uses: for example, DMX512 cannot support a network designed to transmit sound and scenic actuators on the same transmission medium as lights.

Rules references

ANSI E1.11 - Entertainment Technology USITT DMX512-A - Asynchronous Serial Digital Data Transmission Standard for Controlling Lighting Equipment and Accessories

ANSI E1.20 - Entertainment Technology RDM - Remote Device Management over USITT DMX512

ANSI E1.17 - Entertainment Technology ACN – Architecture for Control Networks (Multipurpose Network Control Protocol Suite)