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CEC command syntax

To understand how CEC messages are constructed, let's use the famous CEC-O-MATIC sample:


The first byte (F0) consists of the logical source (or "initiator", first character) and destination (or "target", second character) addresses of the messages. This message is from an unregistered device (F) to the TV (0.) List of logical addresses

The second byte (64) is the command number. 64 is the "set OSD string" command. You can find a list of commands in the HDMI spec or in CEC-O-MATIC.

Then, depending on the command, the following bytes are the parameters of the command. In our example, 00 is the "display control" parameter set to "display for default time", and 48:65:6C:6C:6F:20:77:6F:72:6C:64 is the "OSD String" parameter set to "Hello world".

Other hints to discover CEC