RDM stands for Remote Device Management. This is the colloquial name for the ANSI E1.20 standard.
RDM allows bi-directional communication over the DMX512 cable. This occurs on the twisted pair connected to pins 2 and 3. This same pair of wires is used to transmit data from the console to the dimmers or moving lamps.
RDM requires a certain type of DMX splitter that can monitor the data for a command to reverse the direction of the cable.
The large benefit of this approach as opposed to using the spare pins 4 and 5, is that RDM can be retrofitted to installations wired with single pair cable. A second benefit is that many products already contain the electronics needed for bi-directional communication using pins 2 and 3. These products can be upgraded to RDM with a software only change.
RDM provides the following benefits:
- Ability for the console to set the base address of the lamp. There will no longer be a need for DIP switches.
- Plug and Play. The console will be able to search the DMX512 cable for all connected devices and then automatically patch them.
- Lamp personality: It will be possible for the console to use RDM to download personalities direct from the moving lamp. No more last minute panics to find the correct lamp library.
- RDM devices can be firmware upgraded via the DMX512 signal.
- RDM devices can send status and fault information back to the console.
- By allowing bi-directional communication, it will be much easier to mix DMX installations with sophisticated Ethernet protocols such as Art-Net or ACN.
A full copy of the standard can be purchased from the PLASA web site. For further reading on RDM, you may wish to consult: Control Freak: A Real World Guide to DMX512 and Remote Device Management by Artistic Licence CEO, Wayne Howell.