Civil Engineering Reference
In-Depth Information
neous network and therefore a reduction of the number of different protocols, the
only solution can be to establish a clear and feasible migration plan.
5.1.2
The Application of CAN in Today's Vehicle Networks
The CAN protocol is, in today's vehicle networks, primarily used for the following
three domains:
• Body electronics and active systems of passive safety,
• Chassis domain and driver assistance and
• Engine domain.
The main applications in the body domain deal with the control of windows, doors
and flaps, mirror adjustment, control of lights, seat adjustments, climate control and
comfort access. For cost reasons, the low-speed CAN plays a significant role but is
in competition with the LIN bus. The safety electronics require a fast and safe data
transmission; thus, the interconnection of the ECUs is, in most cases, realized by
the high-speed CAN.
Chassis control systems as well as driver assistance functions put rather demanding
requirements on the safety of the data communication and on the timing. Even if the
high-speed CAN does not allow for a deterministic data transmission, high bandwidth
can provide a sufficiently low latency in many applications. This implies, however,
that only 50 % of the maximal data-transfer capacity can be exploited. Experience
has shown that, beyond this level, non-deterministic latencies begin to rise. The CAN
protocol contains a number of supervisory functions and error recognition concepts:
• Cyclic redundancy check (check of test sums),
• Frame check (check of frame length and structure),
• ACK error (proof of acknowledgment),
• Bit stuffing (error check on bit level by stuff bits) and
• Level monitoring (monitoring of the bus level by the connected ECUs).
• These features and the multi-master concept for the bus access are the founda-
tions why the CAN bus has become a very reliable interconnection technology
which has extended, beyond its original scope, the automobile into field bus ap-
plications in automation technology.
5.1.3
CAN and AUTOSAR
For the software architecture of ECUs, the international AUTOSAR standard has
become increasingly widespread. The acronym AUTOSAR means AUTomotive
Open System ARchitecture (see also Sect. 6.2). Within the software, one can speak
of architecture if the application level as well as the system basis level is realized in
a defined, structured manner. One speaks about an open architecture if the interfaces
are standardized and disclosed. Usually, a certain independence from technologies
