Communication - Description

DESCRIPTION

The primary on-board communication network between the microprocessor-based electronic control modules in this vehicle is the Controller Area Network (CAN) data bus system. However, on vehicles equipped with the optional two-mode Hybrid Electric Vehicle (HEV) technology, Hybrid Local Area Network (H-LAN) data bus and a D-PT data bus are used in addition to the CAN bus.

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 module (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, H-LAN and D-PT busses are each two-wire multiplex systems. 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 all vehicle nodes, except on HEV vehicles. In HEV vehicles, the microprocessors of the Traction Power Inverter Module (TPIM), the Transmission Electro Hydraulic Control Module (TEHCM), the Transmission Control Module (TCM), the Battery Pack Control Module (BPCM) and the Accessory Power Module (APM) use the H-LAN bus to communicate with each other and with other electronic modules in the vehicle through a Hybrid Gateway Module (HGM). The the TPIM has a direct D-PT bus connection over which it communicates with the Powertrain Control Module (PCM) (also known as the Engine Control Module/ECM). However, in addition to the CAN bus network, certain nodes may also be equipped with a dedicated Local Interface Network (LIN), Serial Controller Interface (SCI) or a K-Line serial link bus to provide direct communication between that node and certain sensor inputs.

There are actually three separate CAN bus systems used in the vehicle. They are designated: the CAN-B, the CAN-C and the diagnostic CAN-C. The CAN-B and CAN-C systems provide on-board communication between all of the nodes that are connected to them. The CAN-C and is the faster of the two systems, providing near real-time communication (500 Kbps), but is less fault tolerant than the CAN-B system. The H-LAN and D-PT busses also communicate at 500 Kbps. The CAN-C is used typically for communications between more critical nodes, while the slower (83.3 Kbps), but more fault tolerant CAN-B system is used for communications between less critical nodes. The CAN-B fault tolerance comes from its ability to revert to a single wire communication mode if there is a fault in the bus wiring.

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

The Diagnostic CAN-C bus is also capable of 500 Kbps communication, and is sometimes informally referred to as the CAN-D system, to differentiate it from the other high speed CAN-C bus. The Diagnostic CAN-C is used exclusively for the transmission of diagnostic information between the Front Control Module (FCM) and a diagnostic scan tool connected to the industry-standard 16-way Data Link Connector (DLC) located beneath the instrument panel on the driver side of the vehicle.

All vehicles have a Central Gate way (CGW or FCMCGW) or hub module integral to the FCM that connects to all three CAN buses. This gateway physically and electrically isolates the CAN buses from each other and coordinates the bi-directional transfer of messages between them. Vehicles equipped with the HEV technology also have a separate HGM secured to a bracket on the front of the Transmission Auxiliary Oil Pump (TAOP) module located in the left rear corner of the engine compartment. This separate gateway module isolates the H-LAN bus from the CAN bus and coordinates the bi-directional transfer of messages between the LAN bus and the CAN bus connected to all other nodes in the vehicle.