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must use the same language. This language is
called a protocol.
At present, Ford uses three different data bus
systems. Depending upon model and equipment
level, all three data bus systems are used. Each
of these data bus systems has its own protocol.
Data bus systems
ISO 9141 bus
The International Organisation for Standardisation
ISO 9141 bus. This consists of a single wire and
is used exclusively for communication between the
modules and the Ford diagnostic unit. The fault
memories of the various modules are read out via
the ISO 9141 bus.
Local Interconnect Network (LIN) bus
The LIN bus is a standard specifically designed for
cost-effective communication between intelligent
sensors and actuators in vehicles. The LIN control
unit subnet is used in every situation where the
bandwidth and versatility of CAN is not needed.
The LIN specification comprises the LIN protocol,
a standard format for describing a complete LIN
and the interface between an LIN and the
application. An LIN comprises a LIN master and
one or more LIN slaves. The LIN utilizes the
master/slave principle for the purpose of bus
access control. This has the significant advantage
that few resources (CPU performance, ROM, RAM)
are required for bus management in the slave
module. The master is implemented in a control
module or a gateway which has the necessary
resources. All communication is initiated by the
master. Consequently, a message always consists
of a header, which is generated by the master, and
a response from the slave. The data transfer rate
is in the region of up to 20 Kbit/s. The LIN master
knows the time sequence of all data which are to
be transmitted. These data are transmitted by the
corresponding LIN slaves (e.g. ultrasonic sensors)
if they are requested to do so by the LIN master.
LIN is a single-wire bus, i.e. the data are
transmitted in the cable via one wire. Usually the
same cable is also used to provide the supply
voltage. The ground connection of the supply
voltage also acts as the ground connection of the
data transmission. An LIN does not use a
terminating resistor.
Controller Area Network (CAN) bus
This consists of two twisted wires and operates
serially (data is transmitted sequentially). It is used
for communication between the modules
themselves and between the modules and the Ford
diagnostic unit. The modules are connected to the
data bus in parallel. New modules can be
incorporated easily, without modifying the other
wiring or modules. The transmitted data is received
by every module connected to the control unit
network (CAN). As each data packet has an
identifier (label), in which the priority of the
message is determined as well as the content
identification, each module can detect whether or
not the data is relevant for its own information
processing. This enables several modules to be
addressed with a particular data packet and
supplied with data simultaneously. For this
purpose, it is ensured that important data (for
example from the ABS) is transmitted first. The
other modules are only able to submit their data to
the data bus after the high-priority messages have
been received.
The advantages of the CAN bus are:
• Minimization of wiring requirements
•
High degree of error protection (fault / fail-proof)
• Robustness
• Good extendibility
• Prioritization of messages
• Inexpensive
• Automatic repetition of faulty messages
• Independent system monitoring and the ability to disconnect faulty modules from the data bus
automatically
Due to the increased number of modules and the
resulting continued increase in data transfer, two
different CAN bus systems are used. Essentially,
they only differ in terms of their data transmission
rates and application areas.
To be able to distinguish between the individual
CAN bus systems, the CAN bus system with the
high transfer speed is called the high speed CAN
bus (HS-CAN). The data are transmitted at a baud
rate of 500 kB/s.
The CAN bus system with the medium transfer
speed is called the medium speed CAN bus
(MS-CAN) and is mainly used for communication
in the comfort electronics or the multimedia system.
The data are transmitted at a baud rate of 125 kB/s.
An interface (gateway) is used to exchange data
between the HS-CAN and the MS-CAN. This
provides the connection between the three CAN
databus systems and is installed in the GEM and
in the electronic instrument cluster. The number of
modules which are connected to the three databus G1030779en
2008.50 Kuga 8/2011 418-00-7
Module Communications Network
418-00-7
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