Civil Engineering Reference
In-Depth Information
communications defined exactly. In addition, the structure of the standard network
is specified by further definitions:
• The types of CAN lines, topology and cable lengths are defined.
• During testing, the standard network nodes communicate with each other. In
this, each node communicates with each node. The type of communications and
content of the messages communicated are defined the same way as the order
and the time delay, in which each node sends messages.
• During several tests, errors are generated and the behaviour of the transceivers is
checked out. The position of the errors in the default network is defined exactly.
• In some tests, a ground shift must be generated; realization, position and value of
the ground shift are defined.
Details of these definitions can be found in the test specification for each CAN
transceiver. Figure
6.6
shows schematically the structure of the standard network
using the example of the CAN low-speed CAN transceiver testing.
6.2.4.2
Upper Tester
Via the—according to the layers of the ISO/OSI model—“upper” interface of the
standard network (IUT), the UT manages and controls the standard network with
the therein-contained nodes and thus has the function of the next higher layer.
The UT offers services
11
that allow the selection and initiation of different types
of ring communication or of single messages. The status of communication and the
standard network can be queried. The UT initiates and monitors changes between
the operating modes of the CAN transceivers and allows the readout of these modes.
6.2.4.3
Lower Tester
At the “bottom” interface of the standard network the LT undertakes the function of
the next lower layer. The LT controls the technical peripherals within the test sys-
tem. The services of the LT allow the generation and control of various defined er-
rors and of the ground shift. The supply voltage can be controlled and, for example,
a resistor decade for the defined application of ohmic bus loads can be switched.
Also the control of the measuring devices takes place via the services of the LT.
6.2.4.4 Supervisor
UT and LT are controlled and coordinated by the TCP (see Fig.
6.4
). The TCP is in
the test system for CAN transceiver realized as the so-called
Supervisor (SV).
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Details of these services can be found in the test specification for each CAN transceiver.
