WRC-CANX / CANR Frequently Asked Questions

1.    1.       On what networks do the WRC CANX and CANR work?

The WRC CANX and CANR function with DeviceNet, CANopen, J1939, SDS and other CAN 2.0, Part A and Part B networks. If you don’t see your network listed here contact WRC for more information on your network compatibility.

2.       What’s the difference between WRC-CANX-xx and WRC-CANR-xx product families?

The primary difference between the two different extender families is the way in which the CAN messages travel. The WRC CANX handles all message transfer internally, while the WRC CANR sends the messages across a fiber link.

         The WRC-CANX-xx family is a group of single unit CANbus extenders. The unit receives a CAN message on one side and transmits it, without processing or modifying the message, on the other side. It is one unit with two CANbus connectors, one for each network side.

         The WRC-CANR-xx is a set of two CANbus extenders. The first unit receives CAN messages and transmits them over a fiber link to the other extender, which receives them, then reproduces the messages on the CANbus without processing or modifying them.

3.       What are all of these different models? Which WRC CANX or CANR should I choose?

We offer many different models of the CANX and CANR in order to meet a wide range of customer needs. The following table provides descriptions of each available CANX and CANR model.

Table 10-1 CANX and CANR Models

4.       Why does WRC offer CANX & CANR extenders?

The WRC-CANX/R Extenders are a family of products that extend the communications cable lengths for DeviceNet, J1939, CANopen and other CAN, V2.0, Part A or Part B serial bus systems. These repeaters serve to:

         extend a network beyond its absolute maximum length (e.g., 500 meters for DeviceNet) at the slowest speed

         implement a longer network for a given baud rate (e.g., pushing a 500K baud network beyond 100 m for DeviceNet)

         provide higher speed baud rates for a given network length

         extend the length of the drop cable (e.g., longer drops than 6 m for DeviceNet)

         provide 2500V electrical isolation between 2 sub-nets.

         allow the user to employ non-linear network topologies (e.g., star, tree, etc.)

5.       What types of connections are available for WRC CANX and CANR extenders?

Please see question 3 if you need to know what connectors come on which WRC CANX or CANR models.

Several of the WRC CANX and CANR extenders come with the 5-pin CANbus connection plug, which accepts cable sizes from 12 AWG - 24 AWG. This is the standard round, mini-style connector (M18) with male pins for copper cable. A standard DeviceNet cord with a female end connects to the CANX or CANR.

         Turck supplies individual connectors ends that can be used to build custom DeviceNet or copper cables (part number B4151-0/16 is a 5 pin, 600V, 9A connector that comes in a male or female variety that will connect to the CANX or CANR). Please refer to www.turck.com to find a distributor near you.

         If you are interested in purchasing pre-fabricated cables with the proper DeviceNet connectors, Brad Harrison is the manufacturer of Woodhead P/N 105002A01F030 (male pins) and Woodhead P/N 105000A01F030 (female pins), which are distributed by Gross Automation at http://www.bradharrisonsales.com/ along with many other 5-pole plug in options. All Woodhead products that are compatible with WRC CANX and CANR are called mini-change cordsets.

         Standard Phoenix connectors for use with non-NEMA enclosed units will be supplied with your order if you choose a model using these connectors.

         WRC CANRs use fiber optic receiver/transceivers that are compatible with different fiber grades, so long as they are terminated with ST fiber connectors.

6.       At what baud rates do the WRC CANX and CANR function?

The WRC CANX and CANR function at baud rates of 9.6K, 10K, 20K, 40K, 50K, 100K, 125K, 250K, 500K, 800K and 1M fixed and will auto-detect the baud rate on DeviceNet. The CANX and CANR are also capable of handling different baud rates on each side (e.g., a network with a baud rate of 125K plugged into Network side A can communicate with, through the CANX or CANR, a network with a baud rate of 1M on Network side B).

7.       Does the WRC CANX or CANR require additional termination resistance on the data lines?

The WRC CANX or CANR functions as the beginning or ending of a new segment of the network. With no power supplied to the network, the resistance across the CAN data lines should be  approximately 60 ohms (two 120-ohm resistors in parallel—one on each end of the network bus).

         The WRC CANX has two user-selectable 121-ohm resistors on board. Keeping the plastic jumpers, which are installed on all units at the factory, on W1 and W3 will keep these resistors in the circuit, across the CAN data lines. In this case, the user needs only to terminate the other end of each side of the bus with a 120 ohm resistor to insure correct termination on Network side A (on one side of the CANX) and Network side B (on the other side of the CANX). If your network is already terminated at the beginning and end of the bus (net resistance of ~60 ohms), it will be necessary to take the W1 or W3 jumpers off so that the network is not improperly terminated.

         The WRC CANR has one user-selectable 121-ohm resistor on board, which is selected or deselected using the plastic jumper (installed on all units at the factory) on W1. With the jumper on, this resistor remains in the circuit across the CAN data lines. In this case, the user needs only to terminate the other end of the bus with a 120-ohm resistor to insure correct termination. If your network is already terminated at the beginning and end of the bus (net resistance of ~60 ohms), it will be necessary to take the W1 jumper off so that the network is not improperly terminated.

       It should also be noted that drop lines should not be terminated where they are connected to the main trunk line. For a CANX or CANR in this position the jumper will have to be removed. See the diagrams below for further clarification of proper network setup.

Figure 1 Sample WRC-CANX Setup

8.       How do I determine the location in my network at which I might need a WRC CANX or CANR?

         Drop Line: The WRC CANX or CANR should be used in a drop line when you would like to extend the drop more than 6m.

         Trunk Link: The CANX or CANR should be used in the main trunk line when you desire to extend a network beyond its maximum length (e.g., 500 meters for DeviceNet at 125K baud rate or beyond 100 m for DeviceNet at 500K baud rate)

Differences in baud rate: The WRC CANX and CANR can pass communications from two different baud rates back and forth with each other (e.g., Network A at 125K and Network B at 500K)

Isolation: The CANX and CANR can provide 2500V electrical isolation between 2 sub-nets.

9.       Does the WRC CANX or CANR act as a node on the network?

No. The WRC CANX and CANR are repeaters, which remain completely invisible to the master device or PLC. The unit does not have a MAC ID. It will only pass messages through (without modifying them) and cannot generate its own messages.

10.   How much power does my WRC CANX or CANR require and what is the best means of supplying it?

The WRC CANX and CANR should be powered with 11-25Vdc provided by the DeviceNet network, or other DC power supply. The WRC CANX and CANR Series 4 consume approximately 1.5W (60mA at 25Vdc). Power is typically taken from the bus on each side and each side (A and B) requires power. Power applied to the A Side powers the entire unit except the B Side isolated transceiver. If isolation is not required for your application, then the power line may be jumpered from side A to side B. Care must be taken that the power supply is capable of handling the entire load on both sides of the CANX.

11.   Is there a limit to the number of times a network can be extended using a WRC CANX or CANR?

There is no technical limit to the number of WRC CANXs or CANRs that can be placed in a network. The number of extenders in a network is generally dictated by the length limitations, due to the operation baud rate, of the network desired. Also, although the CANX and CANR have very small propagation delays, their delay times add up when there are multiple units on one network. For this reason, the master device’s EPR time should be adjusted to be greater than the message transmission time (which includes the transmission time on the data lines plus the propagation delay of the CANXs or CANRs) when adding several CANXs or CANRs to your network.

12.   How do I know how many WRC CANXs or CANRs my application will require?

While there is no set formula for determining the number of WRC CANXs or CANRs, the length of the network you are trying to create is most likely the dictating factor in the answer to this question. The lengths of drop and trunk lines must follow CANbus guidelines for the selected protocol. A CANX or CANR should be added in the network whenever you desire to extend the length of a drop or trunk line beyond the normal maximum allowed length. Please refer to the WRC CANX or CANR User’s Manual section Cable Lengths for more information on the allowed cable distances for each baud rate and network protocol.

13.   What do the LEDs on the WRC CANX or CANR tell me about how the unit(s) are behaving?

The Network LEDs on a CANX will be green and blinking slowly if a connection is established, but no messages are being transmitted/received. They will be solid green when messages pass. These same LEDs will be red if there is no connection. The same diagnostics apply for the NSA LED of a CANR, but the NSB LED of a CANR indicates the status of the remote unit and whether the fiber link is hooked up correctly (blinking green with no messages, solid green with messages) or incorrectly (red). The MS LED gives the status of the unit. If it is green the unit is operating normally. If it is blinking red the unit is out of memory, while solid red means the device has failed and may be need to be power cycled or be repaired. Please refer the WRC CANX or CANR User’s Manual and see the section on LED Operation.

14.   Do WRC CANX and CANR extenders cause signal delays, and what speed of messages can they handle?

The WRC CANX has a small propagation delay of approximately 810s, while the CANR has a delay of about 880s. The Series 4 units have increased buffer sizes from Series 3 and faster message forwarding as well.

15.   What testing has WRC completed to guarantee the reliable operation of CANX and CANR extenders?

The WRC production and engineering teams have rigorously tested the CANX and CANR extenders at a variety of strenuous network speeds and environmental conditions with many different network configurations. Although there is no official ODVA test for this type of device, the CANX and CANR have been included in the circuit while running the ODVA conformance testing for a slave device. The slave device passed WRC’s in-house protocol conformance test with the CANX or CANR in the circuit, between the master and slave. The CANX and CANR also passed the in-house execution of the OVDA physical layer test. Each CANX or CANR pair is tested for functionality individually before leaving our facility.

16.   How does the Series 4 WRC CANX or CANR differ from the Series 3 model?

Single Mode fiber cable is now an option, available with the Series 4 CANR. New switch settings allow selection for CANopen speeds up to 1M baud in addition to the standard DeviceNet baud rates. There are larger internal buffers, which allow the WRC CANX and CANR to store more messages while forwarding them in a first-in-first-out manner, making it even less likely that a message will ever be lost in transmission. There is shorter latency time compared to CANX and CANR series 3. The CANX and CANR also feature improved reverse voltage protection and CAN data lines noise immunity.

17.   Does the WRC CANX or CANR come with a warranty?

Yes, the WRC CANX and CANR, like all WRC products, are covered under a two year factory warranty from the date of invoice that all hardware furnished under order will be free from defects in material, workmanship and design.

18.  How are field programming updates accomplished?

In the event that your WRC CANX or CANR is in need of an update, contact WRC. We will discuss with you the options you have for your network.