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RDM General Implementation Discussion General Discussion and questions relating to implementing RDM in a product.

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Old March 25th, 2015   #1
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Join Date: Jan 2015
Posts: 10
Default RDM Responder Tests and background DMX

I have trouble running tests with DMX in background. The tests are run on Windows with VMware Player and Enttec DMX USB Pro Mk2. Tests are passed, but my LEDs are blinking during testing.
I think this is because some tests are sent not between DMX frames, but they are breaking DMX frame, i.e. not full 128 slots are sent, but sometimes only 2 or 3 while my Responder has four DMX slots.

And this is what happens. My responder gets some values for four slots (say, 0x55), then gets RDM request and process it (this takes sometimes up to 8-10 ms when I save parameters in flash and MCU doesn't respond due to disabled interrupts), then there's broken DMX frame with only 2-3 slots with higher value in this slots (say, 0x77) and Responder now has slots 0x77-0x77-0x55-0x55.

And here's the question: is this normal operation when RDM tests are run not between full DMX frames, but break them at random places?

The picture shows short DMX frame followed by RDM request and RDM response. dt shows BREAK to BREAK time (from DMX to RDM request) of 880 us, which less than 1204 minimum required BREAK-to-BREAK time from Table 6 of E1.11.

Update: Setting high start DMX address for Responder, like 120 or 125, shows that full 128 slots DMX frames are rarely received by Responder during RDM tests run. The blinking could be avoided by driving LEDs with received DMX values only when full set of four slots received, thus dropping short DMX frames completely - this works for me, but I still want to understand if this behavior of RDM tests is normal.

First video shows test with driving LEDs even when only one DMX slot is received - frequent blinking.
Second video shows test with driving LEDs only when all four slots are received - no blinking and gradually increasing brightness.

Last edited by alvangee; March 25th, 2015 at 04:34 AM.
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