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CAN undesired RTR message in tms570

Marcos Diaz
Prodigy 155 points

Hi, we are using the CAN bus of the TMS for receiving and sending from certain id's. Once in a while we can see that a remote frame is sent by this board (with the rtr bit set to 1). We don't want to send an rtr message and never configure it to do it. So, my question is, is there another way of sending a remote frame?

(We saw that in order to send a remote frame, you need to set the txrqst bit of a receive message object, but we never do this.)

Perhaps is an auto-response or something else we are missing.

Thanks in advance.

  • 0
    TI__Guru 68920 points

    Hi Marcos,

    I don't think this is the case, I think you would need to configure the CAN peripheral to send a frame w. RTR set.

    How have you determined RTR is set?  If you have an oscilloscope capture would it be possible to see it?

    Or are you using a protocol analyzer?

  • 0 in reply to Anthony F. Seely
    Prodigy 155 points

    Hi, thanks for answering!

    We saw this in the oscilloscope, and as we could see it happens when there is a lot of traffic in the bus. The frame is always seen immediately after a data frame.

    I will translate this just in case:

    0(start of frame)

    00100110011 ID

    1 RTR

    0 Id Ext

    0 Rsrv

    1000 Datasize

    001011001100101 Crc

    1 Crc delimiter

    0 Ack slot

    111111...

    By the way could you recommend a good data analyzer? Thanks!

  • 0 in reply to Marcos Diaz
    TI__Guru 68920 points

    Hi Marcos,

    I'm not a CAN expert by any means but your decoding seems to match up with the screen shot.

    Might be good to sanity check the bit rate you have programmed against the initial 3 bit wide '000' but
    otherwise it does look like RTR is 1.  I was thinking maybe this was bit stuffing but don't see how it would be with the given ID.

    Might be good if you confirm that all the mailboxes are initialized in the start up code since they are implemented in a RAM.  Would be curious if by initializing the RAM this problem disappears.

    Regarding a CAN analyzer - we have mostly NI USB to CAN dongles here.  I can't really say if these are good or not because I haven't used any others - I think the primary advantage of these is the labview connection and the ability to use them within a larger test env.  The viewer I'm using is pretty basic.   Would be good to see if an analyzer concurs on the decoding though.

  • 0 in reply to Marcos Diaz
    Prodigy 65 points

    Marcos,

    what is the voltage Level of your diagram?  To me it looks like 700 mV. That is neither CANH to CANL( would be 2.0V) nor any of the two signals against ground (1.5 V or 3.5V). So are you sure tghat your measurement is correct?

    Frank

     

  • 0 in reply to Frank Bormann2
    Prodigy 155 points

    The levels are above 2.0v and I measured CANH against ground.

  • 0
    Prodigy 230 points

    Hi Marcos,

    Did you ever receive an acceptable answer to this as I have exactly the same problem. i.e a message set up for transmit only will start sending out remote frames if I send the TMS570 a data message with the same ID.

    Best Regards,

    Andy

  • 0 in reply to Andy Williams
    Prodigy 155 points

    No, I haven't received any answer :( Idk what is going wrong.