Compatibility With Existing DMX Hardware
RDM was designed from the outset to work with existing DMX devices. The use of a different start code ensures all DMX-compliant devices that do not support RDM will simply ignore any RDM messages, however not all DMX devices have been made strictly to the DMX specification, and so devices that do not check the start code of incoming DMX packets will try to interpret RDM messages as DMX packets, which can result in flicker or other types of misbehavior.
Any devices that provide galvanic isolation or buffering on the DMX line (such as DMX splitters) have traditionally been designed to allow transmission in one direction: from the controller to the devices. As RDM requires bi-directional communication these devices will typically fail. Only devices that have been designed with RDM compatibility as a feature will typically work. Older DMX splitters that are not RDM compatible should still reliably send the DMX data, and block RDM communication.
Read more about this topic: RDM (lighting)
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