USB-8473 BusMonitor Error Frame

[don_m]

I am using a USB-8473 to monitor messages sent by a 'new' J1939 module.

The BusMonitor that comes with the USB-8473 is telling me that there are Error Frames on the bus.

Most of the time I am seeing 00 00 01 AA for the first 4 data bytes (although there are other 4 byte messages seen).

Is there a listing somewhere that tells me what that means?

Thanks.

[Adam G]

Hello don_m,

The data you are seeing in the Bus Monitor is coming from the J1939 module you are using. Unfortunately, since we don't manufacture that device, we don't know what the information coming from the device means. They should have provided a manual that can give some insight as to what you should expect to receive from the device, and this manual should tell you what the data you see in the Bus Monitor represents. Please let us know if this helps, and have a great day!

Best Regards,

Adam G 

[Bill_in_Detroit]

don_m:

If you haven't solved the problem, the first thing I would recommend you do is place the bus monitor in "Listen Only" mode.  If you are just monitoring the signal you do not need to be acknowledging frames on the bus.  Secondly, depending on how long the cable is that you are using you may need to add a 120 ohm termination resister between CAN_H & CAN_L.  NI has a pretty good discussion of this at http://zone.ni.com/devzone/cda/tut/p/id/9759.  An improperly terminated connection is a frequent source of error frames.  Also, you may want to check that you have a ground reference for the signal.

I hope this helps.

[don_m]

Thanks, what your saying make sense. I believe that the errors are being caused by the transmitter. In this system there are only two nodes. One node that sends out 3 messages every 20 mSec and the receiver that only listens for the three messages. I am seeing the errors under several different test conditions but for the BusMonitor graphic shown I had the Transmitter talking down a 1 meter cable (shielded, twisted pair) talking into a 120 ohm resistor. The NI USB-8473 was monitoring the bus and taking care of the ACK field. To clear this up (in my mind) is the Transmitter the only node on the bus that sends out Error Frames?

[Adam G]

Hello don_m,

If an error is detected by any node, the node will then abort the transmission by sending out an error frame. Please let me know if you have anymore questions about this problem and have a great day!

Best Regards,

Adam G 

[don_m]

Adam,

Based on your last response how do you know that the Error Frame is being sent by the transmitting device (see your first comment above)(I am also assuming that with the Listen Only Checkbox not checked the USB-8473 will send out Error Frames and terminate transmissions)?

My test scenario only has this new J1939 module which sends out three messages every 50 mSec driving a 1 meter cable into a 120 ohm terminator (also attached at the resistor is the NI USB-8473).

Another way of stating the question... If the USB-8473 detected an error (with the Listen Only Checkbox not checked) would the USB-8473 terminate the transmission and what would you see on the NI-CAN BusMonitor?

Thanks,

Don M

[Adam G]

Hi don_m,

We are still looking in to what is generating the error frame. Beside the error frame you are getting, is everything else being transmitted as it should be? Are you running into any other problems?

Best Regards,

Adam G 

[don_m]

Adam,

Other than the Error Frames it appears that everything else is working correctly. In our system, the transmitter sends out 3 output control messages every 50 mSec. The first message contains 6 - 10 bit control words and 2 - 2 bit binary functions, the second message contains 2 - 10 bit control words and the rest is ignored and the third message is ignored. All the functions operate correctly and if I would have used our RM CAN Canview-USB module to monitor the bus I wouldn't be aware of the errors (because the RM CAN module doesn't report CAN Errors).

Thanks for the help,

Don M

[Adam G]

Hi don_m,

I am still waiting to hear back from R&D and will let you know what they suggest. Have a great weekend!

Best Regards,

Adam G 

[don_m]

Adam,

Hear back from R&D yet?

Thanks,

Don