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Original question:

LAUNCHXL-F280025C: DLC of CAN bus receive data

LAUNCHXL-F280025C: How to get data length of CAN receive message?

yuhua chao
Prodigy 50 points
Part Number: LAUNCHXL-F280025C

Tool/software:

I can't get the actually data length in DLC, it will same as obj setting.

As below, when the send message is 8 length data, but obj setting length is 5.

We will get DLC = 5. Is there have any method to get actually data length?

data length=5,obj length =5, DLC=5 data length=5,obj length =8,DLC=8
data length=8,obj length =5,DLC=5 data length=8,obj length =8, DLC=8

CAN Obj setting:

Read DLC :

  • 0
    TI__Genius 16045 points

    Hi Yuhua,

    The expert is currently out of office today due to US holiday. Please expect a delay in response.

    Best Regards,

    Aishwarya

  • +1 in reply to Aishwarya Rajesh
    TI__Mastermind 37950 points

    Hi Yuhua,

    DLC is an information that is added by the user and it is included in the CAN frame during transmission.  The receiving node will read whatever DLC information is in the CAN frame.  DLC does not provide the number of actual bytes that is received.  The best way to manage what the actual number of bytes is in the frame is to ensure that the DLC information that is sent out during transmission matches the actual number of bytes sent.

    Regards,

    Joseph

  • 0 in reply to Joseph Casuga
    Prodigy 50 points

    Hi Joseph,

    Thanks for the response.

    So is there have any method to check the actual number ?

    And I have another question in CAN object setting.

    When I set two CAN object to receive, I can't receive both message.

    But when I set only one object for each, I can receive.

    Can you help me to resolve this question?

    Thanks.

    CAN initialize :

    receive CAN message and read:

  • +1 in reply to yuhua chao
    TI__Mastermind 37950 points

    Hi Yuhua,

    yuhua chao said:
    So is there have any method to check the actual number ?

    JC: No, you would have to ensure that the transmitting node would send the ACTUAL DLC value that matches the number of bytes that will be transmitted with the CAN data.

    yuhua chao said:

    When I set two CAN object to receive, I can't receive both message.

    But when I set only one object for each, I can receive.

    JC: Both receive message object definitions used the same message ID of 0xFFFFFFFF.  First, this is not correct as extended message ID for CAN is 29-bit long so it should be 0x1FFFFFFF.  Second, check if you have used the correct mask value.  The first object has a mask value of 0, meaning that the first message object (RX_MSG1_OBJ_ID) will receive any message ID.  The second message object (RX_MSG2_OBJ_ID) has a mask value of 0x00EA1300  which means that  any message IDs that match the format xxxx.xxxx.111x.1x1x.xxx1.xx11.xxxx.xxxx(binary) where x=ignore bit value, will be assigned to RX_MSG2_OBJ_ID CAN object.

    Please go through example can_ex8_mask  to see how message ID filtering works.

    Regards,

    Joseph

  • 0 in reply to Joseph Casuga
    Prodigy 50 points

    Hi Joseph,

    Thanks for the answer. I can receive the message which I need.

    With the object setting, is the object number means the priority of can message?

  • +1 in reply to yuhua chao
    TI__Mastermind 37950 points

    Hi Yuhua,

    Yes, lower object numbers have the priority.

    Regards,

    Joseph