Civil Engineering Reference
In-Depth Information
6.2.2.3
Error-Poor Systems by Testing
In considering the above risk factors for buses, it is clear that errors in newly devel-
oped CAN modules are very probable, despite the underlying ISO standard 11898.
This results in a high risk potential with possibly dramatic consequences. This
risk potential can be reduced by detecting the errors before the modules are used in
their real environment.
The solution is therefore
testing
: The indispensable method for locating errors in
the modules is the implementation of systematic and elaborate tests.
A CAN module consists of several layers in the sense of the ISO/Open Systems
Interconnection (OSI) model (see Sect. 6.2.1). To determine the origin of a detected
error, the layers are each considered and tested in isolation.
This section describes the CAN transceiver as part of the physical layer of the
CAN modules. Sought are a test idea and a test system with which implementations
of the CAN transceiver can be tested to ensure that as many errors as possible are
found: “Testing is the execution of a program with the intent of finding errors”.
6.2.3
The Concept of Testing the CAN Transceiver
The need of testing the CAN transceiver is indisputable according to the statements
of the previous sections. However, with an increase of only representative tests, fol-
lowing an appropriate test concept, the probability of error-poor systems increases.
Test methods and test principles must be chosen in a way that the implementation
of the tests minimizes the effects of the risk factors listed in Sect. 6.2.2. In 1999, a
group of semiconductor and automobile manufacturers with partners started proj-
ects in the field of the physical layer of CAN to develop, among other things, an
appropriate test system for the physical layer of CAN.
6.2.3.1
GIFT-Project and ICT-Project
The use of bus systems in fields where high reliability and fault tolerance are re-
quired requires as a solution not only the redundancy
4
which is not always feasible,
but also, in particular, the fault tolerance. A fault-tolerant product fulfils its basic
functionality with reduced performance in case an error occurs.
The lowest layer according to the ISO/OSI model is especially vulnerable. Cable
breaks and short circuits can have a momentous effect on the functionality of the
lowest layer and ultimately on the whole system.
The need for a fault-tolerant bus system led to the development of a low-speed
CAN transceiver that includes a fault-tolerant concept and is able to automatically
4
The principle of redundancy is the following: If a system fails, another one is available that takes
the tasks of the failed system.
