Tel: 905–690–4709 dk@tfwm.com - Darryl Kirkland, Publisher

RDM: The New Standard

Since 1990, the lighting industry has only been a one-way communication world. Actually it started before 1990. In the ‘bad old days’, the communication was like the Tower of Babel; each manufacturer created their own language to talk between the console and the dimmers. In 1990, a standard was implemented called DMX-512. With the adoption of this standard, the tower slowly came down and we had one language. Still, the communication only flowed in one direction, so if you sent out a message you weren’t always sure that it was being received.

The big news is that on March 31st of this year, a new standard was adopted (insert wild and mad applause). With the adoption of this new standard, the devices can talk back to the console.

This is one of the new standards we have been drooling about for over 5 years while the standards committee did its job.

Just to give you some background on how a standard reaches adoption; an idea is proposed, and then a committee is formed to develop the idea. Then a draft is sent out for peer review. After the reviews come back, the committee evaluates all of the comments, sends out a new draft and the process repeats until everyone is satisfied. Many a year can go by for complex standards to go through the process, but the process does work.

Now that the standard has been adopted, manufacturers will start to implement this new way to talk to lighting gear. What is so special about this new standard you ask? It is the prefix “bi” added to the word directional. Now if I want to know that something is listening, I can just ask and get a response. That is the simple answer; the standard itself is 137 pages of very detailed information. The following is a short description of RDM for those of us who have no desire to read the 137 pages.

Quick Definition
RDM (Remote Device Management) is a bi-directional communications protocol developed by the ESTA Technical Standards Program for use in DMX512 control systems. Approved on March 31, 2006, it is the new open standard for DMX512 device configuration and status monitoring. Using only the standard DMX512 pair on pins 2 and 3, RDM allows new RDM-aware and legacy DMX512 devices to share the same physical network.

How does RDM work?
The RDM protocol allows data packets to be inserted into a DMX512 data stream without adversely affecting existing non-RDM equipment. By using a special “Start Code,” and by complying with the timing specifications for DMX512, the RDM protocol allows a console or dedicated RDM controller to send commands to and receive messages from specific moving lights, dimmers, color scrollers, and other RDM enabled devices.

Each RDM device is assigned a Unique Identifier (UID) by its manufacturer. This UID is composed of the Manufacturer’s ID and a “serial” number to uniquely identify the device. The RDM controller or console can search for and identify all of the RDM devices connected to it using a process called “discovery.” Once discovered, the controller can communicate with devices individually or in groups by manufacturer.

All of this RDM communication takes place during the time between standard DMX512 “Null START code” frames of level data and is ignored by existing DMX512 compliant equipment. At any time, all RDM traffic may be disabled, removing any speed penalty or compatibility issues with non-compliant equipment in a show critical environment.

Why do we need RDM?
The DMX512 standard has served the industry well for over 17 years. It made possible the independent development and sale of controllers, dimmers, and moving lights. DMX512 is a simple system of transferring “live level data” from a console to a dimmer, moving light or fixture accessory. Clever schemes have been developed to extend this to other types of control such as lamp on/off, fixture recalibration and the like.

As systems using DMX512 have become increasingly more complex, the limits of these schemes have been reached. Further, DMX512 is “talk only”: there is no cross-manufacturer method of returning information from fixtures or dimmers.

RDM allows explicit commands to be sent to a device and responses to be received from it without the use of typical “set a value on channel 1 and then wiggle channel 10” schemes. Functions such as lamp control, recalibration requests, and fan control become standardized commands for all devices.

Manufacturers, however, are not limited to the standard commands. RDM provides for manufacturer-specific commands that can be defined as needed in order to cope with the requirements of introducing new equipment. As new RDM equipment begins to enter the market, it is important to learn from individual manufacturers exactly what their products will communicate.

If after reading all of that you still are in the dark, don’t worry, your console won’t be, and all you have to do is ask and an answer will appear, which is all we ever wanted.