What does CC 01 mean in a lighting hex dump?
Slot 0 is the DMX512 Alternate Start Code 0xCC, reserved for RDM. Slot 1 is Sub-Start 0x01, the E1.20 message structure. UART prints often show those two bytes before UID or PID.
cc 01 18 09 c8 a0 10 00 00 09 c8 01 00 cd f9 01 01 00 00 00 20 10 00 00 05 30
Why is 0xCC not a DMX lighting slot?
Dimmer data uses start code 0x00. Fixtures that only speak DMX ignore non-zero start codes. RDM slips 0xCC frames between those dimmer frames.
Rewrite Load Example start to 0x00 and this parser returns UNSUPPORTED_START with received 0x00. Kind of a valid Load Example is rdm, checksum pass true.
What is the third byte after CC 01?
Message Length. It counts Start Code through Parameter Data. Checksum is two extra bytes. On Load Example Message Length is 24, frame size is 26, checksum slots 2.
| Offset | Byte | Name |
|---|---|---|
| 0 | 0xcc | Start Code (RDM) |
| 1 | 0x01 | Sub-Start (E1.20 message) |
| 2 | 0x18 | Message Length (excludes checksum) |
Destination UID starts at offset 3. Full field order is on the hex dump guide.
How do I tell CC 01 from Ethernet?
Ethernet hex starts with six destination MAC bytes. A sample all-ones dest plus 08 00 here returns UNSUPPORTED_START (0xff). Lighting RDM on RS-485 is not that stack.
What if byte 1 is not 0x01?
Zero the Sub-Start on Load Example and the parser reports INVALID_SUB_START: expected 0x01, received 0x00. It does not keep parsing UID as if the structure were valid.
How does this relate to DUB FE AA?
Discovery Unique Branch responder bodies classify as dub. They do not start CC 01. The controller DISC_UNIQUE_BRANCH request still starts CC 01. Worked 0xFE encoding is on how to decode a Discovery Unique Branch dump.
What should I paste next?
If the dump starts CC 01, paste the PDU. If it starts 7E and ends E7, read the ENTTEC wrapper note first. Checksums are on how to calculate an E1.20 checksum.
Frequently asked questions
What does CC 01 mean in a lighting hex dump?
0xCC is the E1.20 Start Code. 0x01 is the Sub-Start Code for an RDM message. Together they mark an RDM PDU, not a DMX dimmer frame.
What is the third byte after CC 01?
Message Length. On this GET IDENTIFY Load Example it is 0x18. That count excludes the two checksum slots.
Is CC 01 an Ethernet type?
No. Ethernet dumps start with MAC addresses. Pasting CC 01 into an IP decoder will not yield UID or PID.
What if byte 1 is not 0x01?
This parser reports INVALID_SUB_START. E1.20-2010 messages use Sub-Start 0x01. Other values are not treated as a valid RDM message here.
Does CC 01 mean Discovery Unique Branch?
No. DUB responder bodies start 0xFE then 0xAA. A CC 01 dump can still be a DISC_UNIQUE_BRANCH request from the controller.