Compound Tx setup (eg for OBDii)

Discussion and support for current Advanced Dash Loggers, Sport Dash Loggers and Club dash loggers

Compound Tx setup (eg for OBDii)

Postby adam7 on Thu Jul 27, 2023 11:09 pm

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
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Joined: Thu Jan 15, 2009 2:33 am

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