Consistent CANTimeoutException via CAN-serial interface

[Mike Copioli]

Originally Posted by MattG_3165

OK, looks like it was a signal/noise issue - we are using 6-conductor flat cable for our serial link. Your comment about the 115200bps connection got us thinking about noise, so we shortened our serial cable from six feet down to 2 feet, and now we have our first successful serial connection from the cRIO to the Jag.

Maybe we'll switch our cabling to twisted pair in the future.

Thanks!

Twisted pair is not necessary for CAN even a 1Mbps. You should not have any problem using 6' of cable. We have tested using 30' of cable without any issue. the CAN spec states up to 25 meters of cable may be used at 1mbps. We even removed the termination resistor at the far end of the bus without any CAN errors. In fact when the 2CANS are tested prior to shipping only one termination resistor is used on a bus of 12 2CANs. All can traffic is logged during the test and if ANY CAN errors are detected the unit fails.

I think your problem is probably elsewhere. Check the quality of connection of your termination resistors and cable connectors. If you have access to a CAN tool use it to determine if CAN errors are occurring. If you do not have a CAN tool you may use the 2CAN web dash to determine if there are any errors.

[Mike Copioli]

Also you may have CAN id conflict. Have you verified the individual ID's are in fact discrete by pressing the user button on each Jag?

[MattG_3165]

@Mike: After 48 hours of consistent connection failures between the cRIO and the Jaguar, we've now gone the last two hours without a timeout since shortening the cable. My concern about noise is not on the CAN side, but on the serial connection from the cRIO to the Jaguar. We are running on flat wire, and we put the CAN terminator in the DB9 on the cRIO side of the connection. Running the two protocols on parallel wire pairs within the same cable may have caused crosstalk or noise problems on the serial, especially since the serial connection is at such a high bitrate.

@Joe: I really like your suggestion of moving the CAN terminating resistor over to the RJ-12 connector in order to isolate the serial line, or I may even remove the resistor entirely if it turns out that it's not really necessary (per Mike).

[Mike Copioli]

Originally Posted by MattG_3165

@Mike: After 48 hours of consistent connection failures between the cRIO and the Jaguar, we've now gone the last two hours without a timeout since shortening the cable. My concern about noise is not on the CAN side, but on the serial connection from the cRIO to the Jaguar. We are running on flat wire, and we put the CAN terminator in the DB9 on the cRIO side of the connection. Running the two protocols on parallel wire pairs within the same cable may have caused crosstalk or noise problems on the serial, especially since the serial connection is at such a high bitrate.

Ahh, I misunderstood your statement about the cable length.

Originally Posted by MattG_3165

@
@Joe: I really like your suggestion of moving the CAN terminating resistor over to the RJ-12 connector in order to isolate the serial line, or I may even remove the resistor entirely if it turns out that it's not really necessary (per Mike).

I was not suggesting that you remove one of the resistors, just pointing out that it can work in most cases with only one resistor. We recommend and use both resistors in practice.