Ford Fiesta: Module Communications Network / Communications Network - System Operation and Component Description. Description and Operation

System Operation

System Diagram

Gateway Module

The IPC acts as a gateway to translate messages for the HS-CAN , MS-CAN and the I-CAN . This allows messages to be distributed throughout the 3 communication networks. Modules on the I-CAN do not communicate directly with the DLC so the IPC acts as a gateway for diagnostic communication on the HS-CAN to the I-CAN modules.

Network Termination

The CAN uses network termination to improve communication reliability. Termination modules are located at both ends of the 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 an internal 120 ohm resistor that bridges across the positive and negative bus connection. With two 120 ohm resistors located in a parallel circuit configuration, the total network impedance, or total resistance, is 60 ohms.

The communication network consists of three CAN systems in total:

• HS-CAN
• MS-CAN
• I-CAN

Modules on the I-CAN communicate with the DLC on the HS-CAN .

High Speed Controller Area Network (HS-CAN)

The HS-CAN operates at a maximum data transfer speed of 500 Kbps and is designed for real time powertrain information transfer and control.

Modules on the HS-CAN communicate using bussed messages. The network uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, the HS-CAN allows sharing of information between all modules on the network.

Medium Speed Controller Area Network (MS-CAN)

The MS-CAN operates at a maximum data transfer speed of 125 Kbps and is designed for general information transfer.

Modules on the MS-CAN communicate using bussed messages. The network uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, the MS-CAN allows sharing of information between all modules on the network.

Infotainment Controller Area Network (I-CAN)

The I-CAN operates at a maximum data transfer speed of 500 Kbps and is designed for real time audio and multimedia information transfer and control.

Modules on the I-CAN communicate using bussed messages. The network uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits, and allows sharing of information between all modules on the network.

Modules on the I-CAN communicate with the DLC on the HS-CAN .

Controller Area Network (CAN) Fault Tolerance

NOTE: The oscilloscope traces shown are from the IDS oscilloscope taken using the IDS pre-configured CAN settings. The traces are for both data (+) and data (-) taken simultaneously (2-channel) at a sample rate of 1 mega-sample per second (1MS/s) or greater.

Fault Tolerance Normal Operation

The data (+) and data (-) circuits are each regulated to approximately 2.5 volts during neutral or rested network traffic. As 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 message is sent.

Successful communication of a message can usually be identified by the slight spike at the end of a message transmission. Any signals that are significantly different than the normal CAN waveform may cause network Diagnostic Trouble Codes (DTCs) (U-codes) to set or may cause a complete network outage.

CAN Circuits Shorted Together

In the event the data (+) and data (-) circuits become shorted together, the signal stays at base voltage (2.5V) continuously and all communication capabilities are lost.

CAN (+) Circuit Shorted to Ground

In the event the data (+) circuit becomes shorted to ground, both the data (+) and data (-) circuits are pulled low (0V) and all communication capabilities are lost.

CAN (-) Circuit Shorted to Ground

In the event the data (-) circuit becomes shorted to ground, the data (-) circuit is pulled low (0V) and the data (+) circuit reaches near-normal peak voltage (3.0V) during communication but falls to 0V instead of normal base voltage (2.5V). Communication may continue but at a degraded level.

CAN (+) Circuit Shorted to Battery Voltage

In the event the data (+) circuit becomes shorted to battery voltage, the data (+) circuit is pulled high (12V) and the data (-) circuit falls to abnormally high voltage (above 5V) during communication and reaches battery voltage (12V) for peak voltage. Communication may continue but at a degraded level.

CAN (-) Circuit Shorted to Battery Voltage

In the event the data (-) circuit becomes shorted to battery voltage, both the data (+) and data (-) circuits are pulled high (12V) and all communication capabilities are lost.

CAN Circuit Signal Corruption

Rhythmic oscillations, inductive spikes or random interference can corrupt the network communications. The corruption signal source may be outside electrical interference such as motors or solenoids or internal interference generated from a module on the network. In some cases, an open in either the data (+) or data (-) circuit to a network module may cause the module to emit interference on the one circuit which is still connected. The trace shown is an example of a "sawtooth" pattern transmitted from a module with one open network circuit.

Other corruptions may be present when a module is intermittently powered up and down. The module on power up may initiate communication out of sync with other modules on the network causing momentary communication outages.

Controller Area Network (CAN) Multiplex Messages