RDM V1.0 and Art-Net
 

I'm looking for some clarification regarding an Art-Net RDM implentation that may be solved by someone who has an old RDM draft/review spec.

The Art-Net specification states for RDM data within an Art-Net packet:

The RDM data packet including the StartCode

The current Art-Net software from Artistic Licence, however, sends packets in a format that is incompatible to the E1.20-2006 specification, it especially starts RDM messages within Art-Net packets with SC_SUB_MESSAGE (0x01) instead of SC_RDM (0xcc).

Was there an older review/draft specification where RDM messages did start with 0x01 instead of 0xcc?

The Art-Net implementation of RDM was done based on a variation of several early drafts. I would advise against coding to the draft versions and instead wait for Artistic Licence to update to the final version of E1.20.

The Art-Net implementation was done using the prototype Start Code SC_RDM of 0xF0. Now that RDM is actually released all RDM communication is done using the official 0xCC Start Code.

SC_SUB_MESSAGE has always been present and always been 0x01. You will find a numerous incompatabilities and differences between the draft version that was implemented in Art-Net and the final version that has been released.

Again, I would encourage you to only code to the release version and await the update from Artistic Licence to the release version as well.