RDM History

While RDM is a relatively new protocol for most people, it’s history now stretches back more than a decade…

The High End Systems connection
Much of the early development work of what became RDM goes to the credit of work done at High End Systems (HES). Back in 1999, the predecessor to RDM was created at High End Systems by Scott Blair while developing firmware for automated lighting fixtures. Scott has a long running interest in lighting communication protocols and after developing a few other bidirectional protocols that ran over DMX512 for management of onboard preset data in the fixtures, he turned his attention to developing the HES Talkback protocol. At the time Scott was the lead developer of the EC-2 outdoor fixture for HES. This project finally afforded Scott the time to explore his interests developing a protocol that would allow for the full remote configuration and monitoring of the fixtures across the primary pairs of the DMX512 datalink.

A key component of the HES Talkback protocol was the mechanism for discovering all the fixtures connected to the data link. The Discovery protocol had actually been in existence at HES since the release of Cyberlight back in 1994. The discovery protocol was developed by Status Cue Engineer, Shawn Dube, as part of a method for performing firmware updates in the fixtures. Based on a binary search algorithm, a popular Computer Science excercise, it’s application across a DMX512 datalink was quite novel at the time.

DMX512/2000
That was the working name at the time for the massive effort in ESTA that began in the late 90’s in updating the USITT DMX512 standard originally developed in 1986 which the entire entertainment lighting industry is built on. The original USITT DMX512 standard was elegant in it’s brevity of 5 pages. Being a communication protocol standard of only 5 pages though, it left many details unaddressed and contained much ambiguity. The DMX512/2000 project (which eventually became ANSI E1.11-2004) seeked to reduce the ambiguity by stretching that 5 page document into a hefty 70 pages, all while maintaining full backwards compatibility.

After a contentious early draft of the document was released in the Fall of 1999, Scott began attending the CPWG and DMX512 Task Group meetings in January 2000. One of the issues with this draft was that it prohibited bidirectional communication on the primary pair of the DMX512 data link, something HES had been doing for years already and a core requirement in the HES Talkback protocol. While bidirectionality was never mentioned in the USITT version, it did specify RS485 which is inherently a bidirectional link. When this subject was broached during the meetings that weekend saying the reaction to bidirectional communication over DMX512 was not well received would be a massive understatement. Saying the response was greeted with pitchforks and bats would be a bit more accurate. While the tar and feathers were avoided, the group slowly warmed to the concept as it was informally discussed over the next 2 years.

The Start of Something New
All those that were originally the most opposed to bidirectional communication over DMX512 became the biggest advocates of formally creating a new protocol. With the support from then HES CTO Mike Wood, the intellecual property for HES Talkback was put on the table for ESTA to use. In July 2001, the CPWG voted to officially begin work on the RDM project and the first RDM Task Group meeting was held in November 2001 following LDI. Using the HES Talkback protocol as the basis the group quickly began expanding the capabilities and preparing the first draft.

A New Standard is Born
By the time the group completed the 3rd Public Review cycle, the work was done and the new standard was released in 2006 as ANSI E1.20. RDM became the first new standardized lighting protocol released in our industry since DMX512 was released more than 20 years earlier. While RDM has come a long way from it’s beginnings as HES Talkback, the core components and guiding principals remain unchanged.

In 2010, a new revision of RDM was released adding a few improvements and making a number of corrections in the document discovered since it’s initial release.

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