I know from commercial vehicles that certain frames are broadcast continuously when the vehicle is running. The engine with its own ECU will inform the gearbox which has its own ECU and so on. An engine will broadcast its rpm because other ECUs need the information and broadcasting will save many REQ/RSPs and lower the bus congestion.

I have purchased a CAN dongle that I plan to connect to my car’s OBD connector to read the broadcast data without doing any prior REQs.

• First of all, is this a feasible approach for reading data from a
  car?
• Second, how do I interpret the frame once I have it?
• Third, is there a guide available that describes the address part of the frame?
• Fourth, is there guide that defines the data content of a given frame?
• Fifth, commercial vehicles use J1939 to reserve certain ranges of addresses in the frame’s address. Is there a similar standard for cars?

Thanks