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".