Jump to content

CANbus NMT RTR Not Changing Value

Recommended Posts

I am no CANbus expert (far from it, unfortunately), but I am stuck on a problem with NMT Guarding. I have a Bosch/Rexroth SYHNC hydraulic controller that supports CANbus and CANopen, and a V350-TR34 PLC with a short CANbus network. (More to come, but I have to start someplace).

I am using 500 kbps for a baud rate. There are no other gadgets on the network (yet).

I can place the SYHNC in Pre-Operational and Operational mode from the PLC. I can get data back. However, I expect the NMT status value to alternate with each request to the SYHNC. I know the values to expect, and they're different for Pre-Operational and Operational mode. In both cases, the NMT Status value is stuck at a one of the two expected values.

I have checked the CANbus "sniffer" in Information Mode and I seem to see both values coming back, but I get an error from the SYHNC that appears sporadically and then vanishes. I am in touch with the manufacturer, but I thought I'd ask here to see if anyone has seen similar behaviour - stuck NMT Status values.

I DO get a TPDO Rx response. I get different values coming back in both controller modes, and they seem to be accurate. But I can't trust the network if the status values don't alternate, indicating a heartbeat.


Fred Mason

Link to comment
Share on other sites


Which values do you get in NMT status MI?

Are you sure you are not chaning this MI anywhere in the applicaiton?

See below NMT statuses and check whether they are match the status:

0 - Initializing

1 - Disconnected

2 - Connecting

3 - Preparing

4 - Stopped

5 - Operational

127 - Pre-Operational

Link to comment
Share on other sites

  • 4 weeks later...

Thanks for your response, Ofir. I DO get 127 (pre-operational) and 5 (operational). I have also been able to set bits in the target device. So, my comms seem to be working.

The machine is still being constructed, so I don't get any operational chance to try things out for a little while.


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...