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RDM Interpretation Questions Discussion and questions relating to interpreting and understanding the E1.20 RDM Standard.

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Old October 4th, 2010   #1
CyrilU
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Default RDM discovery trouble

Hello to all,

I try to make a responder for my fixture.
All is good with on responder but
when i put more than one responder the discovery process
is having some trouble.

the serial number of my 3 fixture are :
4179-00006E34/4179-00006EAD/4179-00006EB2.

I test with on "ELC checker" sender : the trouble is that this sender
detect my 3 serials and some more like 4179-00006EBC or
4179-00006E3D ...
I test also with an other sender "TBox RDM" : the trouble is that in the most case, the discovery process never end.

I have read some post in this forum discussing about a similar problem.
Is there already an issue for that type of trouble ?

thanks for your help

Cyril
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Old October 4th, 2010   #2
ericthegeek
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It sounds like you are running into the phantom device problem. There are several things that can cause this to occur:

Responder Firmware Errors:
Make sure that your firmware is correctly handling the upper and lower bounds for the DISC_UNIQUE_BRANCH message. An off-by-one error where your device responds when it shouldn't (or doesn't respond when it should) can appear as a phantom device. A common mistake is to use less-than/greater than comparisons rather than less-than-equal-to/greater-than-equal-to.

I don't think this is what's happening to you. Typically this results in a phantom device with the last digit being one more or one less than the real responder's UID.


Collisions During the Discovery Response:
During the 5.8ms discovery response period, it's common to get collisions on the DMX wire when multiple responders reply simultaneously. Sometimes these collisions can appear to have a valid checksum. A properly written controller will attempt to mute the phantom device, get no response, and continue further down the binary tree.

However, some RDM controllers do this wrong, and add the phantom device to the Table of Devices even if the device does not respond to the DISC_MUTE message. This is a common bug in RDM controller software, and I suspect this is what is happening to you. You'll need to contact them and ask how their discovery routine works. Better RDM controllers will not have this problem.

I have not used an "ELC checker" or the "TBox RDM" so I can't tell you how they behave. To know for sure what's happening you'll need an RDM packet analyzer.
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Old October 11th, 2010   #3
ericthegeek
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Cyril, have you made any progress on this?
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Old October 22nd, 2010   #4
CyrilU
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No, i have contact the supplier, they are working on it.

I'll keep you inform asap
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Old October 22nd, 2010   #5
ericthegeek
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Thanks for the update.

I'd encourage you to attend the ESTA RDM Plugfest in Dallas the weekend of January 22nd. It's a great chance to text your responder with a wide variety of RDM controllers.

I hope the strikes in France aren't effecting you too badly, stay safe!
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Old December 20th, 2010   #6
CyrilU
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Hello to all,

Finally I have some news about the ghost serial number.

The problem was coming from the sender. I don't know what they did but now with their new software version all is going well.

Thanks for your help

Regards

Cyril
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Old December 20th, 2010   #7
ericthegeek
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Glad to hear that you got it resolved.
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