Civil Engineering Reference
In-Depth Information
Fig. 3.18
Gateway—example
the feature appropriately. In case the identifier needs to be changed depending on
the contents of the message, a software interaction is necessary. The basic actions
are comparable to the change of data bytes.
In Fig.
3.18
, a GW consisting of two message objects is shown. Message object
5 is defined as the source object and number 9 as the destination object by the usage
of CUR. The different GW transfer features can be used as described above; they
can be found within the register MOFCRn (here n = 5).
3.4.4.2
Gateway Between CAN- and LIN-Bus
A LIN-compliant node on the XC2000 is implemented on the USIC (Universal
Serial Interface Controller) module. The USIC includes a module internal counter,
which eases the baud rate measurement during BREAK signal. The module in-
cludes a FIFO structure, which allows in combination with the collision detection
feature, to have only a single interrupt for the header and one for the frame response.
For frames copied from one bus system (here CAN) to another or signal groups, it
also eases the usage of writing to the module, as the information can be written at
one time. The application does not need to reserve the occupied message objects for
longer times or to buffer the messages within RAM in this case, as they can directly
be written to the FIFO of the USIC. A CAN message can be copied in only for
transactions from the CAN module to the USIC and then be sent via LIN protocol.
The received amount of interrupts can be reduced as the FIFO structure allows not
to receive the information byte-wise. The speed difference between CAN bus and
LIN is normally quite high in an automotive environment, as the LIN bus has a
maximum baud rate of shortly below 20 kBaud. Therefore, buffering LIN messages
has a high impact on the application.
3.4.4.3
Gateway from CAN to FlexRay
Depending on the XC2000 family device, it is possible either to use a device internal
FlexRay module or to use the CIC-310 as extension device, to enable FlexRay com-
munication. The different baud rates need some buffering, especially transferring
data from the time-driven high-speed FlexRay bus to the (compared to FlexRay)
low-speed event-driven CAN bus. Here the CAN module internal FIFO structures
ease handling the traffic coming from the FlexRay module and have to be sent via
CAN bus.
