What is RDM?

RDM is a bi-directional communications protocol developed by ESTA for use in DMX512 control systems. 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.

What's in it for me?

• RDM devices can be automatically "discovered" by the controller, allowing an automated "equipment check" to be performed.

• Parameters which are set using "DIP switches" or a display on the side of a moving light, such as DMX512 starting slot (address), personality, etc., can now be set directly from the console or RDM controller.

• Status and Error messages from RDM devices can be reported back to the controller, alerting the user to a potential problem.

• An RDM controller could display lamp status and lamp hours of all of the moving lights in a rig.

• Small devices, such as LED set lights, can be manufactured without DIP switches or controls of any type and be installed in inaccessible locations because, by using RDM, the DMX512 slot (address) can be set or changed at any time through an RDM controller.

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. Further, since RDM is bi-directional, devices can send back confirmation of the command as well as responses that indicate state or status: lamp condition (on or off), lamp hours, temperature, voltage, etc.

In the past, proprietary control systems have been developed to provide these capabilities. RDM offers both users and manufacturers a standard protocol on which to build interoperable consoles, controllers, intelligent fixtures, dimmers, and fixture accessories, which can communicate with each other.

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.

What equipment is required for an RDM control system?

A basic RDM system consists of a controller and one or more RDM devices. The controller can be part of the lighting console, a separate box that connects in line between the console and the controlled devices, or part of an Ethernet DMX512-type distribution system. An RDM Controller could also be part of a gateway to an ACN system. As only the primary DMX512 pair on pins 2 and 3 are used, all existing DMX512 cable remains usable with RDM. Existing DMX splitters and opto-isolators will need to be replaced with RDM capable bi-directional units.

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.

When will RDM equipment be available?

The RDM standard was approved by the Technical Standards Program for ESTA on March 31, 2006.  is being developed by the RDM Task Group, a part of the ESTA Control Protocols Working Group. It is presently a Draft ANSI National Standard, BSR E1.20,

Some manufacturers are selling RDM equipment now, and we'll likely see a whole new range of RDM products during the fall trade show season. Since every manufacturer will handle updating their equipment to the RDM standard differently, it is important to ask each manufacturer what RDM means for their products.

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