Module Communications Network System: Other Mercury Sable V

Network Termination

The CAN uses a network termination circuit to improve communication reliability. The network termination of the CAN bus takes place inside the termination modules by termination resistors. Termination modules are located at either end of the bus network. As network messages are broadcast, in the form of voltage signals, the network voltage signals are stabilized by the termination resistors. Each termination module has a 120 ohm resistor across the positive and negative bus connection in the termination module. With two termination modules on each network, and the 120 ohm resistors located in a parallel circuit configuration, the total network impedance, or total resistance is 60 ohms.

Network termination improves bus message reliability by

1. stabilizing bus voltage.
2. eliminating electrical interference.

Gateway Module

The IC is the gateway module, translating HS-CAN to MS-CAN and vice versa. This information allows a message to be distributed throughout both networks. The IC is the only module on this vehicle that has this ability.

Special Tools Illustration Tool Name Tool Number 73III Automotive Meter 105-R0057 or equivalent Vehicle Communication Module (VCM) and Integrated Diagnostic System (IDS) software with appropriate hardware, or equivalent scan tool Flex Probe Kit 105-R025C or equivalent

Scheme 74

Scheme 75

ISO 9141 Communications Network

The ISO 9141 communications network is a single wire network. The ISO 9141 communications network does not permit intermodule communication and is used for diagnostic use only. The only module on the ISO 9141 network is the PAM. When the scan tool communicates to the PAM, the scan tool must request all information, the module cannot initiate communications.

The following fault chart describes the specific ISO 9141 network failures and their resulting symptom

ISO 9141 NETWORK COMMUNICATION FAULT CHART

MS-CAN

The MS-CAN uses an unshielded twisted pair cable of data (+) and data (-) circuits. The data (+) and the data (-) circuits are each regulated to approximately 2.5 volts during neutral or rested network traffic. As bus messages are sent on the data (+) circuit, voltage is increased by approximately 1.0 volt. Inversely, the data (-) circuit is reduced by approximately 1.0 volt when a bus message is sent. Multiple bus messages can be sent over the network CAN circuits allowing multiple modules to communicate with each other. The MS-CAN is used for the IC, the accessory protocol interface module (APIM) the smart junction box (SJB), the driver seat module (DSM), the ACM, the SDARS module, the rear entertainment module (RETM), the liftgate/trunk module (LTM), and the HVAC module communications, and designed for general information transfer. The MS-CAN will not communicate while certain faults are present, but will operate with diminished performance with other faults present. The MS-CAN bus may remain operational when 1 of the 2 termination resistors are not present.

In the event that one of the 2 network circuits (MS-CAN + or MS-CAN -) becomes open to a module on the network, unreliable network communication to all modules on the network may result. The module to which the network circuit is open may repeatedly send network messages indicating there has been partial data received. This type of message is referred to as a negative-acknowledge (NACK) message. Repeated NACK messages may "load" the network with too much activity causing intermittent no communication to other network modules and/or the scan tool.

The following fault chart describes the specific MS-CAN failures and their resulting symptom

MS-CAN COMMUNICATION FAULT CHART

HS-CAN

The HS-CAN uses an unshielded twisted pair cable of data (+) and data (-) circuits. The data (+) and the data (-) circuits are each regulated to approximately 2.5 volts during neutral or rested network traffic. As bus messages are sent on the data (+) circuit, voltage is increased by approximately 1.0 volt. Inversely, the data (-) circuit is reduced by approximately 1.0 volt when a bus message is sent. Multiple bus messages can be sent over the network CAN circuits allowing multiple modules to communicate with each other. The HS-CAN is a high speed communication network used for the IC, the accessory protocol interface module (APIM), the PCM, the steering effort control module (SECM), the 4X4 control module, the restraints control module (RCM) the occupant classification system module (OCSM), and the ABS module communications, and designed for real time information transfer and control. The HS-CAN will not communicate while certain faults are present, but will operate with diminished performance with other faults present. The HS-CAN bus may remain operational when 1 of the 2 termination resistors are not present.

In the event that one of the 2 network circuits (HS-CAN + or HS-CAN -) becomes open to a module on the network, unreliable network communication to all modules on the network may result. The module to which the network circuit is open may repeatedly send network messages indicating there has been partial data received. This type of message is referred to as a negative-acknowledge (NACK) message. Repeated NACK messages may "load" the network with too much activity causing intermittent no communication to other network modules and/or the scan tool.

The following fault chart describes the specific HS-CAN failures and their resulting symptom

HS-CAN COMMUNICATION FAULT CHART

The following chart describes the specific CAN messages broadcast by each module, and the module(s) that receive the message

CAN MODULE COMMUNICATION MESSAGE CHART