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CAN bus activity: why cannot I see my CAN bus activity using MAX and a NI USB-8473?

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I am using a NI USB-8473 and Measurement & Automation Explorer on a CAN bus I know is working.   It does not see any CAN bus traffic.

Any ideas on how to trouble shoot to find out why this hardware is not detecting any signals at all?

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Message 1 of 7

There could be a few different problems. 


Is the speed for the 8473 set the same as your bus?

Is the 8473 wired correctly?

Do you need a termination resistor?

Do you have the correct resistor?


Are you using the bus monitor in MAX to check for traffic?

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Message 2 of 7

Is the speed for the 8473 set the same as your bus?  YES

Is the 8473 wired correctly?  YES

Do you need a termination resistor?  YES

Do you have the correct resistor?  YES  This is on a functioning vehicle.  The CAN bus is certainly there and doing stuff.


Are you using the bus monitor in MAX to check for traffic? YES and it does not see any messages or frames.


I am expecting to find out that this is a software problem.  What I would like is a an example LabVIEW program that automatically detected

the CAN bus operation and figured out the set up details.    As it stands MAX is telling me there is no CAN bus traffic when I know there is.


Any suggestions and what to try next? 

Thank you.

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Message 3 of 7
Unless you are absolutely certain that it's wired properly, I'd try swapping the CAN High and CAN Low wires, in case you have them backwards.  Those are the only two wires you need to connect to the 8473, and it's pins 2 and 7.  We seem to make this mistake regularly.
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Message 4 of 7

If you go into Help > Find Example and then click on the search tab and enter CAN there will be all the examples.  There is a CAN that is pretty basic, you just set the baud rate and interface.  Is is similar to the bus monitor in MAX. 


You could double check the resistance of the wires at the 8473.  You might have accidently put in an extra resistor which could be doing bad things.


If the ohms are correct you could put a scope on the wires to see if you have a clean CAN signal, or if you have a bad connection to the car.


There also might be a self test for the 8473 if you right click on the CAN channel that you can try.  I know that if you do not close the network interface properly on the PCI CAN card, you sometimes have to reset it before it will work again. 

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Message 5 of 7

Thanks for all the suggestions.   I tried flipping the H and L wires, no joy.  And the example, no joy.


Then I got an electrical engineer to take a look.   He blinked once and said "You're on the wrong connector.  Tap off the eight pin connector

instead of the ten pin connector."


I did and now the is pulling in lots of CAN messages.


Thanks again for your suggestions.   John Kirk

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Message 6 of 7
Accepted by topic author JBK

Doh! Smiley Very Happy


We have all been there.  Glad you have it working.

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Message 7 of 7