Hey all. I’ve uploaded another video in my How To Program Using Sidus Link Pro series. As always, there is so additional material here. Check out the video first, then come on back and Geta little more knowledge!

An important thing to understand is DMX, while a truly time tested and amazing protocol, is only half of a control conversation.  What I mean is DMX allows a console to speak to lights.  But it doesn’t allow speaking back.  That’s why RDM (Remote Device Management) exists.

Introduced in 2006, RDM allows the lights to speak back to the console.  Why would this be good?  My favorite reasons is you can use a controller to reconfigure a light without ever touching it.  Is it in the wrong mode?  No problem.  Want to change the address of the fixture?  Too easy.  As systems get bigger and bigger, this capability is a big deal.  All of this, and the RDM messages travel down the same cable your DMX is traveling.  

Before we leave RDM as a topic- I gotta warn you that it can be fussy.  First- every step in your chain from console to fixture must support RDM.  A lot of older Splitters, for instance, do not support RDM.  Second- sometimes you’ll have a regular white flash that goes through your lights.  RDM sends out a question “who is there?” basically, every 1 to 2 minutes.  The white flashes happen because the lighting manufacturers of this misbehaving units didn’t follow the full specification of DMX and the lights are misreading the RMD message as a DMX message.  

Rather than get deep in the woods on this topic, I’m going to suggest that RDM should be turned on while you are flashing out a new location or stage, but should be turned off On the Day.  Saves you a ton of fuss. 

A few more facts about DMX as a protocol: 

• Though the connectors are most often a 5 pin configuration, the protocol only uses three of those wires.  
• DMX is capable of running 3281’ though most people stick to 2000’ or under.  
• DMX is a digital protocol that send out the identical signal down both + and – wires.  Why?  Because if the wire passes near a magnetic field and the signal becomes corrupted, the fixture at the end examines the two signals at the other end to help interpret.  That’s why DMX can go such long distances.
• You can only put 32 fixtures on one line of DMX from the console.  You can use another line from a node or use a splitter if you need more.
• You can run DMX through ethernet (I’m not talking about sACN or Artnet here), but it’s limited to the distance of ethernet cables- which is about 328’.
• Terminating DMX is a safety issue.  The current carried along a line of DMX is enough to stop a heart.

Feel free to ask any sort of followup questions or favorite facts about DMX I didn’t mention. See you next time.

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Mark LaPierre is a programmer in film, television and theater based out of Albuquerque.  He grew up in live entertainment and has been a designer/programmer for musicals, concert dance, live music, circus and corporate.  Mark is a proud member of IATSE, an ETC Eos trainer and an enthusiastic trainer of many other platforms and subjects.  He offers Zoom console training as well as in person.  If you enjoy his content, please consider commenting on his posts on the website to appease the Algorithm.