Vehicle-Bus Interface with GMLAN for Data Collection

Within a few years, nearly every vehicle that General Motors (GM) manufactures will have a microcontroller network known as GMLAN. A few GM vehicles already have the GMLAN network, and more vehicles with GMLAN will appear each year. GMLAN uses the Bosch-designed CAN (Controller Area Network) protocol, and it links all of a vehicle’s various processors or nodes to form an in-vehicle data network. CAN uses a Non-Return-to-Zero protocol, NRZ-5, with bit stuffing, and the network implements Carrier Sense Multiple Access with Collision Resolution (CSMA/CR). GMLAN actually includes two linked CAN buses: a high-speed dual-wire CAN for high-speed nodes and a lower-speed single-wire CAN for other nodes. The primary purpose of the GMLAN network is to improve reliability while simultaneously lowering cost by reducing the numbers of wires, connections, and special-purpose circuits in a vehicle. The GMLAN network also promotes synergism among the vehicle nodes to provide vehicle features that would simply not be feasible without the network. We have developed a Vehicle-Bus Interface (VBI) that allows us to collect test data directly from a vehicle’s nodes via the GMLAN network with a GM Standard Thermal Instrument (STI). The VBI facilitates vehicle testing by greatly reducing the need for external sensors and transducers.