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Issues with DCAN at 1MHz

Ayaz Shahid
Prodigy 140 points
Other Parts Discussed in Thread: AM3359

Hi,

I have a working driver for DCAN on AM335xEVM. It works properly upto 500KHz but it appears that there are a few errors on the line when I try to communicate at 1MHz. 

I am using Komodo as both analyzer and network node. The problem specifically arises when I try to send data from Komodo to DCAN at 1MHz. The line shows Form, Stuff and Bit errors but the received data in DCAN is correct with all parameters and flags properly set in the message object. 

Is there a known issue with DCAN? Or has anyone tried using DCAN at 1MHz without this issue?

  • 0
    Intellectual 810 points

    I'd suggest checking for noise or grounding issues: different transceivers can react differently to different conditions (some can "clean up" dirty signals better than others).  Have you looked at the quality of the signal with a scope?

     (admittedly I haven't tried the DCAN at 1MHz, so I can't comment on that: this is just based on my past experiences with CAN in general, which may be of no help to you).

    Darrin

  • 0
    Prodigy 165 points

    We are using the DCAN0 port out of the AM3359 processor on a custom board at 1 MHz with no errors.  We have not tried it on the AM335xEVM board.

  • 0 in reply to Stephanie Goedecke
    Prodigy 140 points

    @Darrin, thanks for the tip. It is possible that it might be a noise issue and its getting more pronounced at high speeds. I've already tried to increase the tolerance of network but that does not seem to solve the issue. I'll mitigating network noise in connection and see if that helps.

    @Stephanie, I don't get any errors in DCAN controller either but I'm also monitoring the line and it seems that the line has errors (which is probably because write operations of the other node in the network is causing issue). But my concern is that we are using the same node to communicate at 1MHz with HECC and other can controllers as well and the errors pop up only in DCAN's case.

  • 0 in reply to Ayaz Shahid
    TI__Expert 6655 points

    Hi Shahid,

    What about the case if you connect AM335x DCAN with HECC? Are you seeing any issues in this case?

    Are you properly taken case of terminating resistors? How are you connecting AM335x DCAN transceiver with komodo?

    Regards

    AnilKumar

    Please mark this Forum post as answered via the Verify Answer button below if it helps answer your question.  Thanks!

  • 0 in reply to Anil
    Intellectual 660 points

    Ayaz:

    No problem on contacting me directly.  Here are some ideas that come to mind:

    1) Check that you have two 120 Ohm terminating resistors.

    2) Check the slope settings of the CAN transceivers (i.e. the slope input pin).  Sometimes transceivers are wired for lower speeds, like 250K.  For full speed, you normally ground the slope pin.

    3) I don't think this is it, but it is possible that there is PLL jitter.  PLL jitter does affect higher baud rates more than lower.  You should scope the CAN bus and see if every bit is exactly 1.00 us in length (when running at 1Mbps).

    I hope the above helps.

    Thanks,

    JR Simma
    The CAN Experts!

  • 0 in reply to JR Simma
    Prodigy 140 points

    Anil/JR,

    Thanks for your suggestions, let me work on these suggestions and I'll share the results. 

    Thanks!