Western Reserve Controls
WRC-CANR-DF-DN and –SM User’s Manual
PUB 14.2
Revision 4.03
14
5. Operation
Each CANR system receives CAN messages and then packs and transmits the messages over
the fiber link to the other CANR, which produces the messages onto its CAN bus network. The CANR pair
provides electrical isolation between the two CAN sub-networks. It has no CAN address and is logically
transparent to the CAN network protocol. The CANR does not interpret nor act on the CAN messages.
The CAN Bus is connected to the A Side of the CANR-DF and receives its power from the Bus.
Whenever a message is transmitted on the Bus to which the CANR-DF pair is connected, one
CANR-DF receives the message on the side where it was initiated and performs a store-and-forward of
the message to the other side. This action is performed for any valid CAN message independent of who
generated it or to whom it is intended.
There is a propagation delay of the message through the CANR-DF system, consisting of 2 parts:
each CANR introduces approximately a 75 µsec delay, and the transmission time on the fiber link (in both
directions) introduces additional delay.
The CANR Series IV also has the capability for each unit to monitor and report on the status of the
other unit in the pair. The NSB LED on one unit reflects the status of the other unit. In this manner you can
determine the operating status of both units by observing just one of them.
Also the CANR allows you set up the baud rate for both units from just one. See the section on
switch settings, 4.3 above, for more details.
5.1. Application Notes
NOTE: CANR-DF’S ARE ALWAYS USED IN PAIRS!
To help insure ease of installation and reliable operation of your system, the following guidelines
should be followed CANR-DF installation in your CAN network.
Proper CAN bus termination is critical to reliable operation of the network. Set the W1 jumpers
on the CANR’s appropriately.
Other than improper terminators, the most common problem is correct fiber cable connection
and termination. Make sure one cable connects TX on one to RX on the other and vice versa.
Also confirm that the fiber itself is good quality and the ends are correctly polished and
terminated with ST connectors.
Use the on-board LEDs to help determine the health of the fiber cable interconnection.
In Autobaud applications, the baud rate that each device selects will be defined by the first
valid message received from either the CAN-Bus or via the fiber connection from the other
device.
Although multiple CANR’s can be used in series, use only one CANR-DF pair in any network
section. That is, only use one CANR-DF pair per trunk line or drop line.
CANR-DF is not a grounded device and the Bus shield is not connected electrically to the
device. Therefore, follow appropriate wiring practices to eliminate noise and other problems.
Example of a valid drop line applications are shown in the following figures. See Figure 1-1 for an
example trunk line application.
