Ford Galaxy / Ford S-MAX. Manual — part 802

Following introduction of the network, only one switch and the software for adaptation of
the vehicle configuration are required.

Easier to introduce logical functions

The term "logical functions" is used to describe the concept whereby certain events trigger
certain responses. For example, the system is programmed in such a way that if a tail lamp
fails a message is sent via the Controller Area Network (CAN) to the electronic instrument
cluster to warn the driver.

A logical function can be introduced by merely reprogramming the affected control
modules. In the above case this would be the generic electronic module (GEM) and the
electronic instrument cluster. The number of components and cables remains the same.

Simple adaptation of systems to customer demands and market requirements

Vehicle functions can be adapted to customer demands and market requirements, e.g. in
the case of the rear fog lamps. In some countries two rear fog lamps are used, whereas in
other countries only one fog lamp is used on the driver's side. In the past it was necessary
to stock different spare parts for different markets. Now a single part is sufficient to cover
all markets - it just needs to be programmed for the specific market.

Use of similar basic systems for entire series

Similar networks (hardware) can be used for a wide variety of different vehicles.

The vehicles only differ in terms of:

The individual components (modules, sensors, actuated components etc.) which are
connected to the system.
The task(s) of the components.
The definition of the components as standard/optional/accessories.
The configuration/programming of the system.

The layout of the network.

General

The network is made up of a range of control modules (these are also referred to as nodes)
which are connected to each other via two communication cables. Each module has its own
voltage supply and ground connection and receives messages and control commands via
both communication cables.

In the event of a break in the circuit, the modules beyond the break cannot communicate
with other parts of the network.

Network areas with high and low data transfer rates

The network consists of two parts. The area with the higher data transfer rate (HS CAN
bus) transmits signals and messages between the generic electronic module (GEM) and
control modules which are mostly located in the engine compartment. The area with the
lower data transfer rate (MS/MM CAN bus) transmits signals and messages between the
generic electronic module (GEM) and the control modules in the passenger compartment
and in the luggage compartment.

The generic electronic module (GEM) represents the interface between the two areas and
converts the data transfer rate up or down to allow the two areas of the network to
communicate with each other.

Data transfer rates

The Controller Area Network (CAN) uses two data transfer rates.

The HS CAN bus (high data transfer rate) transfers data at a rate of 500 kBit/s.
The MS/MM CAN bus (low data transfer rate) transfers data at a rate of 125 kBit/s. 1

kBit/s = 1024 Bit per second (1 Byte = 8 Bit).

Terminating resistor

In order to avoid reflections and interferences in the CAN bus network, a terminating
resistor is provided for bridging purposes at both ends of the CAN. Each terminating resistor
has a resistance value of 120 Ohm.

For the HS CAN bus, the terminating resistors are located in the generic electronic
module (GEM) and in the powertrain control module (PCM).
For the MS/MM CAN bus, the terminating resistors are located in the generic electronic
module (GEM) and in the electronic instrument cluster.

The two resistors are connected in parallel. The resistance values are as follows:

When the CAN bus is intact, the resistance is approx. 60 Ohm in both areas of the
network.
In the event of a short circuit between the communication lines the resistance is approx.
0 Ohm.

Controller Area Network (CAN) Standard

General

The CAN bus is a standardized system for multiplex communication. This means that
multiple control modules can use the same wires for communication without causing
interference between the different signals.

The Controller Area Network (CAN) Standard specifies the following:

The use of two wires (CAN H and CAN L)
The voltage amplitudes
The structure of the messages
The way in which transmission faults are handled

The lines CAN H and CAN L

The lines CAN H and CAN L must not be confused with the different data transfer rates HS
CAN bus and HS CAN bus. The lines CAN H and CAN L are the paths on which signals are
transmitted within the multiplex communication system.

Communications take place at different voltages via two separate wires which are twisted in
pairs. As a result, the network is less susceptible to interference.

The same message is put out at the same time on both wires with different voltages.

Binary signal 0 = 2.5V on CAN H and on CAN L
Binary signal 1 = 4V on CAN H and 1V on CAN L

The average potential difference between CAN L and ground is approx. 2.3V, or approx.
2.8V between CAN H and ground.

These measured values refer to "normal" communications in the Controller Area Network
(CAN), i.e. cases in which no faults have occurred which would cause the modules to send
out error messages.

NOTE: Certain modules, such as the restraints control module (the module for the SRS
system) and the ABS module or ESP module communicate with their relevant sensors via
a so-called internal CAN bus. The internal CAN bus systems have nothing to do with the
communications on the general CAN bus. Instead, they are only used for the purpose of
transmitting data between sensors and associated modules.

Messages in the Controller Area Network (CAN)

A message comprises the following parts:

An identifier which indicates the identity and priority of the message
Information data (value, information etc.)
A check sum which is used to check whether the message is received in full
And end signal which signals the end of the message

A complete CAN message is referred to as a signal frame.

Priority

Conflicts may arise in a network if several control modules try to send messages at the
same time as each other. This could for example be the case if the driver applied the
brakes while the front passenger adjusted the A/C settings and a rear passenger operated
the electric rear window regulators. The messages need to be prioritized so that safe
operation can be ensured. In addition, any delays arising as a result of the prioritization
process must be kept within limits so that the customer preferably does not notice them at
all.

In order to avoid conflicts and delays and to ensure perfect operation of the systems, a
fixed ranking order applies to the messages.

The priority of a message is defined by the number of zeros at the start of the message;
the more zeros, the higher the priority.

Prioritization takes place as follows:

If the network is available, all modules waiting to send a message deliver the first bit of
their message.
All modules register the signals sent out on the network.
If a zero is sent out by a module then the modules which sent out a "1" wait until the
network is available again.
The modules with a zero then send the second bit of their message.
If a zero is sent out by a module as its second bit then the modules with a "1" wait until
the network is available again. This process is repeated.

The message with the highest priority, i.e. the message with the largest number of zeros at
the start, is sent first.

The end of a message is made up of seven zeros. It shows the modules that the network is
free again and that messages can be sent out again according to their priority.

Two message types

Two types of message are sent in the system:

Periodic signal frames are sent regularly to indicate the current status of a parameter.
They are used for types of information which change frequently, e.g. vehicle speed
signals.
Event-related signal frames are only sent if certain conditions are met. They are used for
types of information which occur more rarely, e.g. the opening or closing of a window.

The messages may also incorporate an update bit which shows how "new" the message is.

The system always assumes that the messages reach the intended recipient, so no receipt
acknowledgement signals are sent out. Replies are only sent in response to direct queries
from other modules.

However, a receiver module also knows how often it should receive a particular status
message. If the message is not received then the receiver module can launch an
emergency running program and/or set a trouble code (DTC).

Compatibility

The modules must all speak the same language and be compatible with each other. As a
result, a standardized communication protocol is used.

The language of the modules is contained in the signal configuration. If the signal
configuration of a module does not match the configuration of the other modules than the
module cannot communicate with them. This means that all modules must have a
compatible signal configuration.

In order to check this, the generic electronic module (GEM) sends out an identification
number for its signal configuration via the Controller Area Network (CAN). The other
modules compare this number to their own number. If the identification does not match
then the module stores a trouble code (DTC). The signal configuration is changed
occasionally, so that new messages are added and old ones are removed.

Configurations

The following information is downloaded when a system is configured:

Type of control modules contained (e.g. generic electronic module (GEM)) - task
assignments for the individual modules (e.g. this is the module for the driver's door))
Functions contained (e.g. alarm function on or off)
Connected components (e.g. whether or not the inclination sensor is relevant for the
alarm function)
Output an input messages for each module
Storage locations for various data

The configuration needs to be adapted for any accessories which are installed and needs to
be downloaded again if a module is replaced. The diagnostic unit is used for adaptation and
downloading.

NOTE: Two vehicles which otherwise appear identical may behave differently if they have
different configurations. Parameters may have been changed by the customer or by the
workshop.

Error management in the Controller Area Network (CAN)

General

The Controller Area Network (CAN) is monitored by the generic electronic module (GEM). If
the GEM detects a fault in the CAN bus then a trouble code (DTC) is stored in the GEM.
There are different types of DTC according to the fault type:

No communications from the module
Faulty communications

No communications from the module