Testing - CAN System Engineering - page 295

memory, but this cannot be accomplished anticipatorily. Obviously, first the error
must be stimulated and then subsequently the error memory can be read in order
to perform the error-detection check. Additionally the entry must not be persistent.
A simple trial-and-error process to check whether a TC with a test pattern can be
successfully applied is not suited for a validation process. If, as described above, a
test does not adhere to an appropriate sequence of test steps or initial states are not
checked, tests erroneously may lead to a “fail” or “pass” verdict. Referring to the
example, a standard conforming implementation erroneously would result a “fail”
only because the error memory would not yet have stored the expected error when
reading the error memory. Vice versa, there are cases in which wrong implementa-
tions may erroneously be judged as conforming implementations. Referring to the
above example, this would be the case, if the erroneous test object would perma-
nently indicate an error and the tester would not check the—wrong—initial state.
A validation must prove that such kinds of errors do not exist and that only a
conforming behaviour of a test object results in a “pass” verdict. In order to meet
the process requirements of ISO/IEC 17025 (see [ISO17025]), a technically appro-
priate and fully documented validation of a test system is a condition sine qua non,
which nevertheless corresponds to a rather high quality level.

6.2 CAN Transceiver Conformance Tests

This section addresses the testing of controller area network (CAN) transceiver.
They are a part of the CAN physical layer. The general standardization of CAN has
already been described in earlier sections. In Sect. 6.2.1, first the standardization of
physical layer of CAN will be discussed. Section 6.2.2 gives an introduction to why
it is necessary to submit systematic tests to the CAN transceiver before their use
in real applications. Subsequently, the test idea underlying the tests is presented in
terms of test method and test principle in Sect. 6.2.3. The structure of the test system
is described in Sect. 6.2.4. At the end of this section, the TCs and their focal points
for different CAN transceiver implementations are described in Sect. 6.2.5.

6.2.1 Standardization of the Physical Layer of CAN

For a general history and standardization of CAN, see the sections before.
The parts 2, 3 and 5 of the ISO 11 898 are the relevant standards of the CAN
physical layer and are briefly introduced below.

ISO 11898-2: High-speed, medium-access unit The standard ISO 11898-2 is the
most implemented standard of CAN physical layer. It describes the functional 1
and physical 2 interface to the transmission medium. Also, the specification of the

1 Functional interface: Medium-Dependent Interface (MDI).
2 Physical (electrical, optical) and mechanical interface: Physical Medium Attachment (PMA).