Description And Operation: Communication: Description

DESCRIPTION 

The primary on-board communication network between micro-controller based electronic control modules in this vehicle is the Controller Area Network (CAN) data bus system. A data bus network minimizes redundant wiring connections; and, at the same time, reduces wire harness complexity, sensor current loads and controller hardware by allowing each sensing device to be connected to only one Electronic Control Unit (ECU) which is also referred to as a node. Each node reads, then broadcasts its sensor data over the bus for use by all other nodes requiring that data. Each node ignores the messages on the bus that it cannot use.

The CAN bus is a two-wire multiplex system. Multiplexing is any system that enables the transmission of multiple messages over a single channel or circuit. The CAN bus is used for communication between most vehicle nodes. However, in addition to the CAN bus network, certain nodes may also be equipped with a Local Interface Network (LIN) data bus. The LIN data bus is a single wire low-speed (9.6 Kbps) serial link bus used to provide direct communication between a LIN master module and certain switch or sensor inputs. There is also a private security bus network between the Radio Frequency Hub (RF-Hub) Module and the Keyless Ignition Node (KIN) known as the Security K Line Communication Bus.

In this Powernet Architecture, there are three separate CAN bus systems used in the vehicle. They are designated as:

• CAN Chassis (CAN C) - the termination resistors are integral to the Star Connectors.
• CAN Interior High Speed (CAN IHS) - the termination resistors are integral to the Star Connectors.

The communication protocol being used for the CAN data bus is a non-proprietary, open standard adopted from the Bosch CAN Specification 2.0b.

These networks and their subnetworks are protected by a Security Gateway Module (SGW).

These CAN bus networks provide on-board communication between all of the nodes that are connected to them. The CAN C and CAN-ePT networks are the faster of the CAN systems providing near real-time communication (500 Kbps). The CAN C is used typically for communications between more critical nodes, while the slower (125 Kbps). The CAN IHS system is used for communications between less critical nodes. The CAN-ePT network is used on this vehicle exclusively for PHEV system ECUs. These networks comprise the electronics architecture known as PowerNet.

The added speed of the CAN data bus is many times faster than previous data bus systems. This added speed facilitates the addition of more ECUs or nodes and the incorporation of many new electrical and electronic features in the vehicle.

The Body Control Module (BCM) is located under the instrument panel to right of the glove box. The central CAN gateway or hub module integral to the BCM is connected to CAN IHS and CAN C buses. This gateway physically and electrically isolates the CAN buses from each other and coordinates the bidirectional transfer of messages between them.

All ECUs transmit and receive messages over one of these buses. Data exchange between the ECUs is achieved by serial transmission of encoded data messages (a form of transmission in which data bits are sent sequentially, one at a time, over a single line). Each ECU can both send and receive serial data simultaneously. Each data 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 ECU uses arbitration to sort the message priority if two competing messages are attempting to be broadcast at the same time. Corruption of a single bit within a message will corrupt the entire message. Each message contains a Cyclic Redundancy Check (CRC) which specifies the message size exactly. If the message detected conflicts with the CRC the ECU receiving it will determine the message to be an error and consider that communication has not been possible. Diagnosis of this condition using a lab scope may reveal activity that appears to be bus data messages even if no actual communication is possible. Communication problems that affect the whole bus, as a result of opens and terminal push outs are more likely to occur on data busses that operate at a high speed than a data bus that operates at a lower speed.