Testing - CAN System Engineering - page 301

For that reason, the conformance testing of the CAN transceivers is performed in
a network that consists of a defined number of CAN nodes 7 . Thereby, the behaviour
of each individual CAN transceiver is observed and compared with the behaviour
expected of it. At the same time, however, the behaviour of the CAN transceiver in
its entirety is considered in a network. The TCs are determined such that during the
testing each CAN transceiver communicates with the other.
The respective maximum specified in ISO 11898 is chosen as the number of
considered CAN transceiver.
The structure of the network is specified in detail as a so-called default network
in the test specifications for CAN transceiver. The definition of the standard net-
work was developed under the ICT project and takes into consideration the realistic
and relevant conditions of use for CAN modules.
There are two types of network tests.

• Homogeneous network: For homogeneous network tests, the standard network
is equipped with CAN transceivers of only one manufacturer.
• Heterogeneous Network: In a CAN network, CAN transceivers from different
manufacturers must communicate as error poor as possible. By that reason, for
heterogeneous network tests CAN transceiver from different manufacturers are
considered in their joint behaviour. When equipping the standard network, the
positions for the CAN transceivers from the different manufacturers are defined
in the test specification.

The decision to carry out conformity tests as network tests, in conjunction with
a systematic TC determination, impacts a significant reduction of the risk factors
listed in Sect. 6.2.2, entanglement of a module with its environment .

6.2.3.5 Test Case Determination

It has already been mentioned that a test object, must not only demonstrate that it
meets the functionality defined in its specification, but also show that it meets the
specified functionality even under conditions that correspond to its later field of use.
Ideally, conditions and events that describe the environment of a test object in
a broader sense are listed in the specification. In practice, this is unfortunately of-
ten not the case. The specification of the CAN transceiver and the associated test
specifications, however, were developed or revised in cooperation with users (au-
tomobile manufacturers), manufacturers (semiconductor manufacturers) and a test
house. Therefore, it can be assumed that the determination and compliance with
real application conditions is well done, because the group members have different
perspectives and at the same time a wealth of experience.
In practice, the test of a product can generally only be a selection from a very
large amount of possible TCs. This clearly shows that a systematic test case deter-

7 Another reason is the difficulty to satisfactorily emulate the bus-side interface of the CAN trans-
ceiver with its complex dynamic impedance and time response by appropriate generators.