Class 2: An Introduction to Medium Speed Multiplexing 920222
Serial data link communication throughout a vehicle has become an important area for new technology application of automotive engineering during the last several years. As the electronic content of vehicles increases, so does the need to transfer information between the various sensors, controllers, and actuators in that vehicle.
This paper will discuss Class 2, General Motors' innovative version of the SAE J1850 Recommended Practice for Class B Data Communications Network Interface. An introduction to J1850 and related multiplexing topics will be followed by an explanation of the details of the Class 2 serial data link protocol. There are many benefits of using Class 2 including: the ability to standardize messages across vehicle types; one corporate database; the ability to change the size of the network easily due to the “open architecture” of the protocol, etc.
A custom integrated circuit, the Data Link Serial/Parallel (DLCS/P), developed and built by Delco Electronics Corporation to interface serially/in-parallel to a host microprocessor, will also be discussed. This IC contains both the transceiver circuitry and digital logic fabricated with a 40 volt High-Voltage CMOS (HVCMOS) process.
Finally, the message structure and strategy used in actually transferring data between engine, transmission, chassis, body, instrument panel, etc. controllers will be introduced.