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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 February 24th, 2016   #1
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Default What NACK to use for messages sent to Subdevices ?

What NACK should be used for messages sent to SubDevices when the PID in question is only defined for use with the Root Device ?

For Example, GET:PARAMETER DESCRIPTION sent to SubDevice NNN.

If the Subdevice does NOT exist, then it is logical to report SubDevice Out of Range, without considering the PID in questiion.

But if the subdevice DOES exist, should the response still be NACK: SubDevice Out of Range, or is NACK: Unsupported PID acceptable ?

To my mind, the use of NACK : SubDevice Out Of Range applies as part of the "addresssing" determination, and before any processing of individual PIDs.

If a PID is targetted at a valid SubDevice, use of NACK:Unknown PID is logical for both the case of "never known to subdevices because it is a Root Only PID", and "not known to this Subdevice for whatever reason", but the NACK should still come from the valid subdevice.

As far as I can tell, the standard does not speak to an order of processing fields within a received message, so potentially both NACKS are legal ?

Discussion ?
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