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Compound Tx setup (eg for OBDii)

PostPosted: Thu Jul 27, 2023 11:09 pm
by adam7
Im looking into how to get OBD-II parameters into my SDL3, and can see that Motec have helpfully provided templates for this. Ive successfully used these, and also modified them get the specific parameters that I wanted. However, I need a little help to explain how the CAN Tx in compound format works, specifically the frequency of each of the component messages. For example, with the follow setup

Base Address: 7DF Transmit Rate 100Hz
Message Type: Compound
ID Offset ID ID_Mask
1 1 010C FFFF {requests RPM}
2 1 010D FFFF {requests Speed}
3 1 010C FFFF {requests RPM again :-) }
4 1 0106 FFFF {requests Short Term Fuel Trim}
9 1 0107 FFFF {requests Long Term Fuel Trim }
10 1 012F FFFF {requests Fuel Level }

From experimentation I can see that rate of the transmitted requests will be ~88Hz "shared" between the components 1-8, and ~12Hz shared between components 9-16. So in the above example RPM would be requested at a rate of ~22Hz (100 * 0.88/8 * 2 ) and Fuel Level 6Hz. (100 * 0.12/2 *1)
Does that make sense and correct?

Ive got DTN00019, are there any further tech notes that I can have access to taht will help me understand the comms setup?

Thanks Adam