Hybrid Bus: Notes

WARNING: This page is about a different car, the 2007 Chrysler PT Cruiser. However, it is still accessible from the selected car via links, so may be relevant.

Either the Controller Area Network (CAN) data bus or the hybrid bus system that integrates the Programmable Communications Interface (PCI) data bus with the CAN bus allows all electronic modules or nodes connected to either bus to share information with each other. Regardless of whether a message originates from a module on the lower speed PCI or CAN-B bus or on the higher speed CAN-C bus, the message structure and layout is similar, which allows the Totally Integrated Power Module/Central GateWay (TIPM or TIPMCGW) or the separate gateway module to process and transfer messages between the buses. The TIPM also stores a Diagnostic Trouble Code (DTC) for certain bus network faults.

All modules (also referred to as nodes) transmit and receive messages over one of these buses, either the single-wire PCI bus or the two-wire CAN bus. Data exchange between nodes is achieved by serial transmission of encoded data messages. Each node can both send and receive serial data simultaneously. PCI bus messages are carried over the data bus in the form of Variable Pulse Width Modulated (VPWM) signals which, when the high and low voltage pulses are strung together, form a message. On the other hand, each digital bit of a CAN bus message is carried over the bus as a voltage differential between the two bus circuits which, when strung together, form a message. Each node in either bus uses arbitration to sort the message priority if two competing messages are attempting to be broadcast at the same time.

The voltage network used to transmit bus messages requires biasing and termination. Each module on the PCI bus network provides its own biasing and termination. Each node terminates the bus through a terminating resistor and a terminating capacitor. There are two types of nodes used in the PCI bus network. The dominant node terminates the bus through a 1 KW resistor and a 3300 pF capacitor, typically resulting in about a 3300 ohm termination resistance. However, this resistance value may vary somewhat by application. The separate gateway module is the only dominant node in the PCI bus network. A non-dominant (or recessive) node terminates the bus through an 11 KW resistor and a 330 pF capacitor, typically resulting in about a 10800 ohm termination resistance.

There are also two types of nodes used in the CAN bus network. On the CAN-C bus, a dominant node has a 120 ohm termination resistance while a non-dominant node has about a 2500 to 3000 ohm (2.5 to 3.0 kilohm) termination resistance. Except on vehicles with the 1.6 liter engine, the CAN-C bus on this vehicle has two dominant nodes: the Powertrain Control Module (PCM) and the TIPMCGW. On vehicles with the 1.6 liter engine, the two dominant CAN-C nodes are the separate gateway module and the TIPMCGW. The termination resistance is combined in parallel to provide a total of about 60 ohms. This resistance value may also vary somewhat by application, depending upon the number of nodes on the bus.

NOTE: All measurement of termination resistance is done with the vehicle battery disconnected.

NOTE: Termination resistance of a CAN-B node cannot be verified with a Digital Multi-Meter (DMM) or Digital Volt-Ohm Meter (DVOM). The transceiver of each CAN-B node connects to termination resistors internally. When the vehicle battery is disconnected, the internal connections of all CAN-B node transceivers are switched open, disconnecting the termination resistors. Therefore, the total bus resistance measured under these conditions will be extremely high or infinite, which does not accurately reflect the actual termination resistance of the CAN-B bus.