NI-CAN + NMEA 2000 connection problem

[david.gregory]

I'd like to get NMEA 2000 messages from marine electronics onto my computer so that I can translate those messages into another format (I guess that's where LabVIEW will come in).

I've connected a USB-8473 to an Actisense NGT-1-ISO NMEA 2000 to PC gateway and they're not working together; I get error code 3FF6206B* from Bus Monitor and no message traffic.  I believe the -8473 is working as I get an amber light for the USB (though the only time the CAN light flashes is briefly at the start of Bus Monitor) and it passes a MAX self-test.  I've tested the NGT using Actisense's NMEAReader software and traffic looks good there; I see several pieces of equipment on the network as expected.  (I should note that I used a different computer to test this as our preferred computer doesn't have a serial port to be compatible with the NGT directly.)

So, what am I doing wrong? What settings should I be paying attention to?

One cause of suspicion is the baud rate: NMEAReader claimed 115.2 kbd, but I can't get that setting in the -8473 properties in MAX.  Using the advanced settings (which I don't understand), the closest is 115.942 kbaud; the list gives three values, but each of these yields the same error situation.  NMEA 2000 is supposedly 250 kbd, but neither that nor the default 125 work either. 

*For your reference, that's "CAN bus problems detected (no ack), but communication is proceeding. This warning corresponds to CAN Error Passive state. Solutions: Verify that the cabling is correct, devices are connected and operational, and proper bus power is applied."  Not sure what communication is referred to or what an ack is.  I believe cabling is correct -it's just serial and USB - and devices are operational, just maybe not properly so.

[DiscoBall]

Hi David,

I believe NMEA 2000 is a protocol based on J1939 (which is based on CAN). KnowledgeBase 2T7F3V8RL: Can My NI CAN Card Interface with My (CAL, CANopen, PCAL, SDS, CAN Kingdom, J1939, J1850 etc.) Device? shows that NI-CAN does support J1939, but you will want to enable the option as shown in the KB.

The baud rates could be an issue also. Here is the link to the Philips AN97046 to determine BTR values exactly.

Can you enable the J1939 option and get the baud rates to match up? Get any errors afterwards?

[david.gregory]

Thanks for the links, Joshua.  I hadn't gotten as far as the Frame/Channel API - I was just trying to see traffic on Bus Monitor.  Should I leave the Monitor aside for now and enable that?

The baud rates still don't match up, or at least I'm still getting the same error no matter what I try using MAX (method 1 in the link you provided).

Or is this more due to the nature of CAN vs. NMEA 2000? Talking with the helpful folks at Actisense (the NGT maker), they've said:

"...the NI device will not operate correctly on the NMEA 2000 network (as it's not certified) so will cause other issues if it tries to transmit anything back to the bus." and then "If you never transmit CAN packets back to the bus via the NI product (receive only), then technically you should be able to get away with it. Any transmissions from the NI device could have a negative effect on the network integrity."

So, does the USB-8473 automatically transmit when connected? Can I put it into a silent mode? Down the line I think we would want to be transmitting back, but I'm willing to settle for crossing only one bridge at a time.

[DiscoBall]

HI David,

CAN devices do respond in a way during the ACK portion of another node's transmitted CAN frame. You can put your NI device into Listen Only mode with the Bus Monitor options. Listen only makes the device passive and it will not transmit acknowledgements. This is "silent mode".

While the baud rates may be correct, you mentioned in your original post that the cable you were using is just a  serial cable. Have you taken care to add appropriate termination resistors to your CAN network? See KnowledgeBase 3IABNOHS Proper Termination for NI-CAN Hardware (High Speed, Low Speed and Single Wire.... The baud rates you are using fall under high speed.

I wish I had a NMEA 2000 device laying around so I could test this myself, sorry.

[david.gregory]

Sorry for the gap in replies, Joshua.  I think the network is set up, and terminated, correctly.  We use the standard NMEA terminators on both ends of the network "backbone" and I haven't seen any problems while using NMEAReader, reading directly off the NGT-1-ISO.  (By the way, we've spliced on a serial connector to our NGT.  So the setup is NMEA network-NGT-serial/usb converter cable-PC when using NMEAReader; since the -8473 has a serial connector built in there's no need for the converter cable.)

I did try operating in Listen Only mode in Bus Monitor.  Error code is now "- - -" which I guess means no error, but there's still no traffic appearing: Busload is 0%.  Tried this at 125 and 250 kbaud as well as the three BTR settings for 115.9 kbaud.

I'm wondering if there are more basic problems here, like if the hardware is working.  Besides the MAX self-test, is there any way to make sure the -8473 truly is working?

[VPEA]

Hello David,

Did you ever resolve this issue?  I am communicating with a Garmin GPS 19x with NMEA 2000 protocol using XNet with success.  However, I am not able to read the messages with a payload (DLC) greater than 8.  More specifically it is GNSSPosData, Hex: 1F805, PGN:129029 that I am trying to read.  Per the NMEA 2000 protocol this is at least a 51 length payload.  Did you find a way to read the larger payloads?

Steve

[j_bou]

Hello Steve,

Seeing as your issue is different from the original question posed by david.gregory, I would recommend posting this question in a new thread. There is a greater chance that you will receive a response from the community as your question will be contained in a dedicated thread. In addition, it will be searchable by others in the community if ever they run into the same issue.

However, if you are waiting for a response specifically from david.gregory then feel free to wait for his response.

Regards,

j_bou

[VPEA]

Good suggestion.

I posted a new question.  "How do I read the larger than 8 byte messages from a NMEA 2000 databus using XNET?"