Description

DESCRIPTION

The primary on-board communication network between microprocessor-based electronic control modules in this vehicle is the DaimlerChrysler Programmable Communication Interface (PCI) data bus system in combination with the Controller Area Network (CAN) data bus system, which forms a hybrid 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 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 bus is a two-wire multiplex system, while the PCI bus is a single-wire multiplex system. Multiplexing is any system that enables the transmission of multiple messages over a single channel or circuit. The CAN-C bus is used for communication between all vehicle powertrain and chassis nodes, including the Powertrain Control Module (PCM), the Controller Antilock Brake (CAB), the Steering Angle Sensor (SAS) and the Electronically Controlled Clutch (ECC) (also known as the All Wheel Drive/AWD) module. The CAN-B bus is used for communication by the Occupant Restraint Controller (ORC) and the Power Liftgate Module (PLGM), while all of the remaining body and interior nodes use the PCI bus.

In addition to the CAN and PCI bus networks, 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. The premium Tire Pressure Monitor (TPM) trigger modules communicate directly over LIN bus circuits with the Wireless Control Module (WCM), which is a LIN master. Also, the right and left front smart window motors communicate directly over LIN bus circuits with their respective Passenger Door Module (PDM) or Driver Door Module (DDM), which are both LIN masters.

There are actually three separate CAN bus systems used in the vehicle, along with the PCI and LIN bus systems. 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 is the faster of the systems, providing near real-time communication (500 Kbps), but is less fault tolerant than the CAN-B system. 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. Slower still, the PCI bus communicates at 10.4 Kbps.

The added speed of the CAN and PCI hybrid data bus network is many times faster than 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 Body Control Module (BCM) 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. The DLC also has a circuit connected directly to the PCI bus.

All vehicles have a Central GateWay (CGW) or hub module integral to the BCM that is connected to all three CAN buses and the PCI bus. This gateway physically and electrically isolates the CAN and PCI buses from each other and coordinates the bi-directional transfer of messages between them.