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LAUNCHXL-F280049C: About short circuit in DCAN module

lei li
Intellectual 375 points
Part Number: LAUNCHXL-F280049C
Other Parts Discussed in Thread: SN65HVD232

Hi,

    I shorted circuit CANH and CANL.And see the figure below for the waveform：

   My question is:

1、According to this waveform, what frame format was this？

2、The first Low level time was 17 bit times; and the later low level time was 1 bit time. Does such a waveform have any special meaning?

  Thanks!

  • 0
    TI__Guru* 95315 points

    You have not mentioned if there are other nodes on the bus or if 280049 Launchpad is the only node. What is also important to know is exactly what the CAN module is doing when you short the bus. 

    lei li said:
    1、According to this waveform, what frame format was this？

    It is likely an error frame.

  • 0 in reply to Hareesh Janakiraman
    Intellectual 375 points
    Hareesh Janakiraman said:
    You have not mentioned if there are other nodes on the bus or if 280049 Launchpad is the only node.

    There have none other nodes on the bus. Only shorted circuit CANH and CANL in 280049 Launchpad.

    Hareesh Janakiraman said:
    What is also important to know is exactly what the CAN module is doing when you short the bus. 

    My customer is trying the experiment, and I don't know the details.

    Hareesh Janakiraman said:
    It is likely an error frame.

    But, I noticed that it is neither "active error frame" nor "passive error frame".

  • 0 in reply to lei li
    TI__Guru* 95315 points

    The 17-bit low-time could be an active error frame. 

    I did try the experiment on my  side with a 280049 Launchpad and did not see the waveform shown. Without more details on exactly how this experiment was done and what the objective is, we can't help further. Refer to www.ti.com/lit/spracq3 for ideas on generating different types of error.

  • 0 in reply to Hareesh Janakiraman
    Intellectual 375 points

    I'm so sorry! The customer clarified a fact to me. They used F28335 to try the experiment. It can generate the above waveform， if  shorted circuit CANH and CANL in only one CAN node. So can you explain the waveform further?

       Thanks!

  • 0 in reply to lei li
    TI__Guru* 95315 points

    What is the CAN module doing while the CANH and CANL pins are shorted? Is it idle or is it trying to transmit? Can you attach the oscilloscope waveform of CANTX & CANRX pin when this experiment is being done? Exactly what is the objective of this experiment?

  • 0 in reply to Hareesh Janakiraman
    Intellectual 375 points

    The CAN module was sending data frame while the CANH and CANL pins are shorted. And I  attach the oscilloscope waveform of CANTX & CANRX pin in the experiment. The yellow waveform is CANTX.

    In addition, the purpose of my customer is:  whether the bus can be restored in the event of a CAN failure.

       Thanks!

  • 0 in reply to lei li
    TI__Guru* 95315 points

    If the objective is to determine "whether the bus can be restored in the event of a CAN failure", I don't believe this is a valid experiment. Most of the CAN transceivers offer some level of short-circuit protection. This includes shorting of CANH or CANL with supply or GND. This also includes shorting CAN_H & CAN_L together. Once this error condition is removed, the module should recover on its own after the elapsing of 128x11 recessive bit-times.

    In any case, I tried this experiment on my setup and did not see the waveform you had attached in the post. I only see CANTX pin staying at 3.3v when I shorted the CANH & CANL pins.

  • 0 in reply to Hareesh Janakiraman
    Intellectual 375 points

    Hi,

       Thank you very much for your reply!

      

    Hareesh Janakiraman said:
    In any case, I tried this experiment on my setup and did not see the waveform you had attached in the post.

            Did your experiment in F28335 or F280049? My customer  did the experiment in F28335.

  • 0 in reply to lei li
    TI__Guru* 95315 points

    I tried it on a F38335 device connected to a SN65HVD232 transceiver.

  • 0 in reply to Hareesh Janakiraman
    Intellectual 375 points

    Thanks very much! By the way, is the CAN module sending data frame while  CANH and CANL are short-circuited? My customer  did that so.

  • 0 in reply to lei li
    TI__Guru* 95315 points

    Yes, the CAN module was transmitting data at a very high bus-load.