Concorde V6-2.7L VIN V (2001)
Information Bus: Description and Operation
Vehicle Communication
VEHICLE COMMUNICATION
The Chrysler Programmable Communication Interface multiplex system (PCI bus) consists of a single wire. The Body Control Module (BCM)
acts as a splice to connect each module and the Data Link Connector (DLC) together. Each module is wired in parallel to the data bus through its
PCI chip set and uses its local ground as the bus reference. The wiring is a minimum 20 gage. The PCI bus wire insulation color will be violet with
a yellow tracer. An extra tracer color may be added along with the violet to help distinguish between different node connections.
The bus is designed to handle a maximum number of nodes to meet all of the bus load and timing requirements. The bus resistance and
capacitance is designed to provide a maximum level of filtering without distorting the bus symbols. This is why extra capacitance and resistance
should not be added to the PCI Data Bus circuitry.
In order for an electronic control module to communicate on the PCI data bus, the module must have bus interface electronics consisting of a
transmitter/receiver (or transceiver) and Logic control, bus termination for loading and filtering the bus, and wiring which interconnects the
system.
Because of the unique coding scheme used in the PCI bus, each module is required to have logic control. The data moving on the bus is called
symbols. The interface logic performs the following functions: encode and decodes binary data into symbols, synchronizes all bus symbol timing
and edges, controls the sending and receiving of messages, monitors for bus arbitration, monitors for corrupted symbols due to noise and controls
the transceiver.
The bus logic control also provides the transceiver with the information it needs to transmit symbols on the bus. The transceiver controls the
waveshaping of each symbol that it transmits by using internal voltage controlled current drivers. When the bus transceiver is turned ON, the bus
driver ramps up the voltage to the set range and maintains this voltage until the driver is turned OFF, at which time the voltage is ramped back
down to the low voltage, ground. The transceiver is designed to allow for arbitration between modules. If more than one module is trying to access
the PCI bus at one time, the code determines the message that has the higher priority, and is then allowed to access the bus first.
The PCI bus requires a resistance and capacitance termination load to ground to operate. Because each bus transceiver can only source current to
the bus, the resistance load is required to sink this current and pull the bus to ground on the falling edge of the symbols. The bus resistance is
minimum of 315 ohms to a maximum of 2 K ohms. The termination capacitance is required for noise filtering and to help in the symbol wave
shaping. The bus capacitance shall not be greater then 12,000 pf.
Each module on the PCI bus has a small termination load of a parallel resistance and capacitor to make up part of the over all bus termination load.
One or two modules on the PCI bus may have a higher load termination to provide stabilizing influence over the variations of vehicle builds.
These modules, called dominant modules, may very for car line to car line. The Powertrain Control Module (PCM) is the only dominant node for
this vehicle.
