Compound Tx setup (eg for OBDii)
Posted: Thu Jul 27, 2023 11:09 pmIm 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
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