RDM (lighting)

Last updated July 19, 2024

Remote Device Management(RDM) is an addition to the DMX512 control protocol for stage lighting equipment, introduced in 2006. DMX512 was developed in the late 1980s as a standard protocol for lighting consoles to communicate with dimmers, but has since been used for more complex applications, including the control of intelligent lighting fixtures. The addition of RDM addresses many of the shortcomings of DMX512, which is unidirectional with no support for metadata.

Background

DMX512 has been the standard for the control of theatrical lighting devices, including intelligent lighting fixtures, since the mid-1990s. DMX512, based on the RS-485 protocol commonly used in industrial control systems, was the first universal standard for the control of stage lighting equipment.^[2]

RDM's predecessor DMX512 is a unidirectional protocol with little capacity for error reporting or automated configuration. A single cable carries one "universe" of DMX512, consisting of 512 "addresses," each of which can be assigned a value from 0 to 255. In the earliest applications of DMX512 networks, a control console would be connected to a rack of dimmers. Within the dimmer rack, a single DMX address would control the voltage level of a single dimmer from 0% to 100%.

In more complex applications involving intelligent lighting fixtures, a DMX address is assigned to each function of a fixture, with some fixtures utilizing blocks of addresses numbering in the dozens. A device's identity within the network is defined by the first address of the block it occupies, akin to a static IP address. In a standard DMX network, each fixture must be manually configured with a starting address, and the same starting address must be separately programmed into the control console.^[3]

Applications

RDM serves multiple main functions: identification, status reporting, and configuration.

Identification allows a control console to automatically detect all devices on the DMX network, distinct from their DMX address. This assists the operator in determining which of their devices have even powered on.

Configuration allows the control console to change the address and other properties of a device. This functionality avoids the time-consuming process of manually setting DMX addresses on each fixture. Intelligent lighting fixtures often have multiple control modes and other settings, which can also be configured over RDM with the proper software support.

Status reporting from lighting fixtures enables the operator to view the status of their devices, including faults such as burnt-out lamps or failed motors.

Compatibility

RDM is enabled in many new lighting devices, and can be used in the same network as non-RDM-enabled devices, using existing cabling. DMX512 devices that do not support RDM should ignore all RDM commands, but in practice, some devices do malfunction when receiving RDM signals.

DMX networks may include splitters with opto-isolator functionality, which only allow signal transmission in one direction, and filter out RDM signals. DMX splitters that pass through RDM signals are available, but not all splitters include this functionality.

RDM is a technology specific to DMX512 signals over standard twisted-pair wire. Protocols that carry DMX signal over IP networks, such as Streaming ACN and Art-Net, have their own implementations of remote control which are backwards compatible with RDM.

Technical specifications

RDM Physical layer

The RDM protocol and the RDM physical layer were designed to be compatible with legacy equipment. All compliant legacy DMX512 receivers should be usable in mixed systems with an RDM controller (console) and RDM responders (receivers). DMX receivers and RDM responders can be used with a legacy DMX console to form a DMX512 only system. From a user’s point of view the system layout is very similar to a DMX system. The controller is placed at one end of the main cable segment. The cable is run receiver to receiver in a daisy-chain fashion. RDM enabled splitters are used the same way DMX splitters would be. The far end (the non console or splitter end) of a cable segment should be terminated.

RDM requires two significant topology changes compared to DMX. However, these changes are generally internal to equipment and therefore not seen by the user.

First, a controller’s (console’s) output is terminated. Second, this termination must provide a bias to keep the line in the ‘marking state’ when no driver is enabled.

The reason for the additional termination is that a network segment will be driven at many points along its length. Hence, either end of the segment, if unterminated, will cause reflections.

A DMX console’s output drivers are always enabled. The RDM protocol is designed so that except during discovery, there should never be data collisions. To ensure this lack of collisions, while making possible implementation on different platforms, there are times when all line drivers are required to be disabled. If nothing more than the termination was done, the line would float to some unknown level. In that case one or more random changes might be read on the line. These random changes greatly decrease system accuracy. So the biasing of the line is required

To assure this, section 2.4.1 (Line Bias Networks) of the standard says; “The command port shall provide a means to bias the termination of the data link to a value of at least 245 mV and verified by using the test circuit described in Appendix F.”

The standard further states that, the biasing mean “shall be polarized such that Data+ of the data link is positive with respect to Data- the data link. The Line Biasing network shall maintain this bias when the data link is loaded with the equivalent of 32 unit loads and common mode voltage is varied over the range of +7 volts to -7 volts DC.”

The standard does not require any particular circuit for providing the basis and termination; however, the simplest method is often a passive pull apart network.

Whatever method is used must be tested with the chosen driver chip to see that the design combination still meets the requirement of E1.20. Tests are given in Appendix F of the standard. These tests are for design verification and are not required as production testing. Experience has shown many EIA485 drivers designed for 5 volt operation will pass the required tests. It is not so clear that all 3.3 volt parts will pass. In either case this performance must be verified. Details of the pull apart network and the tests can be found in ANSI E1.20 - 2006.

Protocol

RDM packets are interspersed with the existing DMX data packets being used to control the lighting. The DMX 512 specification requires that DMX packets begin with the start code. The default Start Code is 0x00(also known as the Null Start Code). By using the start code 0xCC, RDM packets can be safely inserted between DMX data packets without older non-RDM aware devices attempting to read them.

The DMX 512 specification required DMX connectors to be a 5-pin XLR type, with only the first 3 pins being used (pins 4 and 5 were reserved for "future use"). Unfortunately, various manufacturers started using the final two pins for various, proprietary purposes, such as low-voltage power or proprietary talk-back protocols. As a result, the decision was made to have all RDM communication on pins 2 and 3. This raises data collision concerns.

The RDM standard addresses this problem by ensuring that in all cases (except discovery) only one device is authorized to be transmitting at any given time. Only the controller (of which there can be only one) can start an RDM exchange. Responders can speak only if spoken to. The controller will always initiate all RDM communication.

All RDM devices have a unique identifier (UID) that consists of a manufacturer ID and serial number.

RDM communication can be broken down into three types:

Discovery

Discovery is the only situation in which data collisions can occur assuming all connected devices behave correctly. The controller will broadcast a discovery command to all devices and await a response. If there are more than one device connected, the simultaneous responses will likely result in a data collision, and the controller will not receive a correctly formatted response. The controller will then refine its search to a smaller range of UIDs according to a binary search pattern. Once the controller receives a correct response it will attempt to mute the responding device. After a successful mute, the device is no longer allowed to respond to discovery messages, and the controller can continue searching for other devices. Once all devices have been muted (no responses are received to discovery commands), the discovery process is finished and the controller will hold a list of all connected devices.

The controller will need to periodically perform searches for new devices and assert that already discovered devices are still connected.

Unicast communication

General communication with a specific fixture occurs in a request-response pattern. The controller sends the request to the device, addressing it by the device's UID. When the request has been sent, the controller relinquishes control of the DMX line for a given period of time, so the device can transmit its response. Unicast communication is the only way in which data can be retrieved from a fixture (other than its UID which can be obtained using the discovery mechanism mentioned above). If the device does not respond within a given period of time, the controller can assume communication has failed, and may retry.

Broadcast communication

To quickly send instructions to multiple fixtures, RDM allows for broadcast communication. This allows the controller to send an instruction to all devices, or all devices from one manufacturer. As more than one device might be receiving the message, responses are not permitted in broadcast communication except during the Discovery process.

Related Research Articles

X10 is a protocol for communication among electronic devices used for home automation (domotics). It primarily uses power line wiring for signaling and control, where the signals involve brief radio frequency bursts representing digital information. A wireless radio-based protocol transport is also defined.

Stage lighting is the craft of lighting as it applies to the production of theater, dance, opera, and other performance arts. Several different types of stage lighting instruments are used in this discipline. In addition to basic lighting, modern stage lighting can also include special effects, such as lasers and fog machines. People who work on stage lighting are commonly referred to as lighting technicians or lighting designers.

KNX is an open standard for commercial and residential building automation. KNX devices can manage lighting, blinds and shutters, HVAC, security systems, energy management, audio video, white goods, displays, remote control, etc. KNX evolved from three earlier standards; the European Home Systems Protocol (EHS), BatiBUS, and the European Installation Bus.

DMX512 is a standard for digital communication networks that are commonly used to control lighting and effects. It was originally intended as a standardized method for controlling stage lighting dimmers, which, prior to DMX512, had employed various incompatible proprietary protocols. It quickly became the primary method for linking controllers to dimmers and special effects devices such as fog machines and intelligent lights.

A dimmer is a device connected to a light fixture and used to lower the brightness of the light. By changing the voltage waveform applied to the lamp, it is possible to lower the intensity of the light output. Although variable-voltage devices are used for various purposes, the term dimmer is generally reserved for those intended to control light output from resistive incandescent, halogen, and compact fluorescent lamps (CFLs) and light-emitting diodes (LEDs). More specialized equipment is needed to dim fluorescent, mercury-vapor, solid-state, and other arc lighting.

A lighting control console is an electronic device used in theatrical lighting design to control multiple stage lights at once. They are used throughout the entertainment industry and are normally placed at the front of house (FOH) position or in a control booth.

RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and multipoint systems are supported. The standard is jointly published by the Telecommunications Industry Association and Electronic Industries Alliance (TIA/EIA). Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Multiple receivers may be connected to such a network in a linear, multidrop bus. These characteristics make RS-485 useful in industrial control systems and similar applications.

Show control is the use of automation technology to link together and operate multiple entertainment control systems in a coordinated manner. It is distinguished from an entertainment control system, which is specific to a single theatrical department, system or effect, one which coordinates elements within a single entertainment discipline such as lighting, sound, video, rigging, or pyrotechnics. A typical entertainment control system would be a lighting control console. An example of show control would be linking a video segment with a number of lighting cues, or having a sound cue trigger animatronic movements, or all of these combined. Shows with or without live actors can almost invariably incorporate entertainment control technology and usually benefit from show control to operate these subsystems independently, simultaneously, or in rapid succession.

Architecture for Control Networks (ACN) is a suite of network protocols for control of entertainment technology equipment, particularly as used in live performance or large-scale installations. For example, lighting, audio or special effects equipment. ACN is maintained by Entertainment Services and Technology Association and its first official release was ANSI Standard E1.17-2006 - Entertainment Technology - Architecture for Control Networks. The standard was subsequently revised and released as ANSI E1.17-2010.

D54 is an analogue lighting communications protocol used to control stage lighting. It was developed by Strand Lighting in the late 1970s and was originally designed to handle 384 channels. Though more advanced protocols exist such as Digital MultipleX DMX (lighting), it was widely used in larger venues such as London's West End theatres which had Strand Lighting dimming installations, and it was popular amongst technicians because all the levels can be "seen" on an oscilloscope. D54 is still supported on legacy equipment such as the Strand 500 series consoles alongside DMX. Generally a protocol converter is now used to convert DMX (lighting) down to the native D54.

A lighting control system incorporates communication between various system inputs and outputs related to lighting control with the use of one or more central computing devices. Lighting control systems are widely used on both indoor and outdoor lighting of commercial, industrial, and residential spaces. Lighting control systems are sometimes referred to under the term smart lighting. Lighting control systems serve to provide the right amount of light where and when it is needed.

<span class="mw-page-title-main">Intelligent lighting</span> Automated light fixtures

Intelligent lighting refers to lighting that has automated or mechanical abilities beyond those of conventional, stationary illumination. Although the most advanced intelligent lights can produce extraordinarily complex effects, the intelligence lies with the human lighting designer, control system programmer, or the lighting operator, rather than the fixture itself. For this reason, intelligent lighting (ILS) is also known as automated lighting, moving lights, moving heads, or simply movers.

AMX192 is an analog lighting communications protocol used to control stage lighting. It was developed by Strand Century in the late 1970s. Originally, AMX192 was only capable of controlling 192 discrete channels of lighting. Later, multiple AMX192 streams were supported by some lighting desks. AMX192 has mostly been replaced in favour of DMX, and is typically only found in legacy hardware.

0–10 V is one of the first and simplest electronic lighting control signaling systems, used as an early fluorescent dimming system. Simply put, the control signal is a DC voltage that varies between zero and ten volts. Two standards are recognized: current sourcing and current sinking.

Digital Addressable Lighting Interface (DALI) is a trademark for network-based products that control lighting. The underlying technology was established by a consortium of lighting equipment manufacturers as a successor for 1-10 V/0–10 V lighting control systems, and as an open standard alternative to several proprietary protocols. The DALI, DALI-2 and D4i trademarks are owned by the lighting industry alliance, DiiA.

Digital Serial Interface (DSI) is a protocol for the controlling of lighting in buildings. It was created in 1991 by Austrian company Tridonic and is based on Manchester-coded 8-bit protocol, data rate of 1200 baud, 1 start bit, 8 data bits, 4 stop bits, and is the basis of the more sophisticated protocol Digital Addressable Lighting Interface (DALI).

A colour scroller or colour changer is an electro-mechanical lighting accessory used in theater, film, dance and concerts to change the colour projected by stage lighting instruments without the need of a person to be in the vicinity of the light. A colour scroller moves plastic "gel" colour gel [actually dyed polyester and/or other base materials coated with dyes] into the beam of the light. It is generally attached to the gel frame holder at the transmitting end of a lighting fixture, so colour is introduced after the beam characteristics have been defined by the optics of the lighting instrument. Most scrollers are controlled via DMX512 protocol, but some models also utilize the RDM protocol. When colour scrollers were first introduced around 1980, a number of companies produced them, including: Avolites, GAM Products, Morpheus Lights, Rainbow, Rosco Laboratories and Wybron Inc. Now the main manufacturers are: A.C. Lighting, Apollo, Morpheus Lights and Rainbow.

<span class="mw-page-title-main">SeaChanger Color Engine</span>

The SeaChanger Color Engine is an electro-mechanical device that is used to control light color in entertainment-industry lighting applications. The unit employs four overlapped color filter wheels, inserted into a light beam near its source, to produce colored light. This is in contrast to color scrollers, which insert color filter ribbons into a light beam. The color engine, which was released by Ocean Thin Films in 2005, is designed to fit into the Source Four lighting instrument made by Electronic Theatre Controls.

Art-Net is a royalty-free communications protocol for transmitting the DMX512-A lighting control protocol and Remote Device management (RDM) protocol over the User Datagram Protocol (UDP) of the Internet protocol suite. It is used to communicate between "nodes" and a "server".

ArKaos is an application for live visual performance, conceived as a visual sampler for video loops that can be triggered from the computer, or through a hardware interface. The application is available in two versions: ArKaos VJ MIDI, conceived as a live video performance instrument, often used in conjunction with a MIDI keyboard, and ArKaos VJ DMX, which can be controlled with a DMX console.

References

↑ "ANSI E1.20 - 2010". Entertainment Services and Technology Association. 2017. Document CP/2009-1017r2.
↑ Knight, Richard; Gottelier, Tony (March 1994). "Automated Lighting - The Sequel: Part 2 - Universal Controllers" (PDF). Lighting and Sound International. 9 (3): 37–47. ISSN 0268-7429 . Retrieved 2023-11-10.
↑ Davis, MIlton (2010). "What Does RDM Mean for the Rest of Us?". Protocol. 15 (3): 32–35. Retrieved 2023-11-14.

External links

RDM Protocol Developer and User Forums

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.

[1] "ANSI E1.20 - 2010". Entertainment Services and Technology Association. 2017. Document CP/2009-1017r2.

[2] Knight, Richard; Gottelier, Tony (March 1994). "Automated Lighting - The Sequel: Part 2 - Universal Controllers" (PDF). Lighting and Sound International. 9 (3): 37–47. ISSN 0268-7429 . Retrieved 2023-11-10.

[3] Davis, MIlton (2010). "What Does RDM Mean for the Rest of Us?". Protocol. 15 (3): 32–35. Retrieved 2023-11-14.

[1]

[2]

[3]