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Old July 5th, 2009   #2
ericthegeek
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Join Date: Aug 2008
Posts: 355
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Your questions pertain more to E1.11 (DMX512A) than to E1.20 (RDM).

> So when I receive a break of 0.99second followed by
> a MAB of 0.99second, this is still a valid signal?

No, it is not a valid signal. Per section 9.2 of E1.11 (DMX512A), a receiver is considered to have "lost data input" if it does not see the falling edge of a break within 1.25 seconds of the previous break's falling edge.

RDM has much tighter restrictions on the break length, so while a DMX controller may send a 0.99 second break, and RDM controller's break must be less than 352 micro-seconds.

> I find it also very unclear what must happen when the
> timing of the incomming signal are not within spec.

What happens when a device loses DMX signal is entirely up to you. You can hold the last data forever, you can shutdown after some timeout, or you can start strobing randomly. All that's required is that you document the behavior.

To quote section 9.2 of E1.11:
"Although this Standard does not specify loss of data handling procedures, manufacturers shall state what their Loss of Data handling procedures are.

> when the MAB is less then 8uS. Must then the
> packet be dropped?

The packet may be dropped, but the standards don't require that the packet be dropped. Older versions of the DMX standard (USITT DMX512/1986) allowed a 4 micro-second MAB, so a well designed receiver may wish to support a shorter MAB.

For RDM, E1.20 has a bit of guidance about when an RDM packet may be considered "lost", but there are no absolute rules. Any RDM device is free to drop any packet at any time for any reason. It's up to the controller to determine how to handle these conditions. If a packet doesn't meet the timing specs, you can ignore it, or you can try to respond if you can. It's up to you.
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