Section 95 (Electronic Control Modules (Service Information)): Communication: Operation: Notes

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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 the bus to share information with each other. Regardless of whether a message originates from a module on the low speed PCI or CAN-B bus or on the high speed CAN-C or CAN-D bus, the message structure and layout is similar, which allows the Totally Integrated Power Module/Central GateWay (TIPM or TIPMCGW) 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. 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. Each node 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 messages requires biasing and termination. Each module on the 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 on the bus. 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 TIPM (or TIPMCGW) is the only dominant node in this 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.