Information Bus: Description and Operation

Communications Network

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

Vehicle communication utilizes both Medium Speed (MS) and High Speed (HS) Controller Area Network (CAN) communications. CAN is used for many modules to communicate with each other on a common network. CAN in-vehicle networking is a method for transferring data among distributed electronic modules via serial data bus. Without serial networking, intermodule communication requires dedicated, point to point wiring resulting in bulky, expensive, complex, and difficult to install wiring harnesses. Applying a serial data network reduces the number of wires, combining the signals on a single network. Information is sent to the individual control modules that control each function.

The vehicle has 2 module communication networks:

- Medium Speed Controller Area Network (MS-CAN)
- High Speed Controller Area Network (HS-CAN)

Network Topology









Network Termination

The Controller Area Network (CAN) uses a network termination circuit to improve communication reliability. The network termination of the CAN bus takes place inside the termination modules by termination resistors. Termination modules are located at either end of the bus network. As network messages are broadcast in the form of voltage signals, the network voltage signals are stabilized by the termination resistors. Each termination module has a 120 ohm resistor across the positive and negative bus connection in the termination module. With 2 termination modules on each network, and the 120 ohm resistors located in a parallel circuit configuration, the total network impedance, or total resistance is 60 ohms.

Network termination improves bus message reliability by:

- Stabilizing bus voltage
- Eliminating electrical interference

Gateway Module

The Instrument Cluster (IC) is the gateway module, translating HS-CAN to MS-CAN and vice versa. This information allows a message to be distributed throughout both networks. The IC is the only module on this vehicle that has this ability.