• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 30 subscribers
  • Views 1480 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

TMS570LC4357: Without CAN Transceiver, try to connect the CAN bus of TMS570LC4357

TMS570LC4357: TMS570LC4357: Without CAN Transceiver, try to connect the CAN bus of TMS570LC4357

Saravanakumar S93
Expert 1300 points
Part Number: TMS570LC4357


Hi all,
As mentioned in the below link feedback,
            e2e.ti.com/.../602843

In small PCB, We have connected the 2 microcontrollers CAN channel with shorter distance.
But, CAN communication is not working with lower baud rate.
  Microcontroller1 Microcontroller2
  CANTX     =>   CANRX
  CANRX     <=   CANTX
With this option, whether CAN communication will work (or) not ?
              https://www.mikrocontroller.net/attachment/28831/siemens_AP2921.pdf

Below are the clarifications,
 #As mentioned, in the above link proposed diagram, Do we need to short both the pins and use along with diode ?
 #In case if we are using CAN bus with diode option, Is there any performance degrading will happen? Eg: More Traffic in the CAN bus
Kindly give your valuable feedback.
Thank you.

Regards,
S.Saravanakumar

  • 0
    TI__Guru**** 197596 points

    Hello,

    If there is no CAN transceivers in CAN network, the approach described in AP2921 can be used at low baud rate and short PCB trace. 

    The CAN transceivers outputs a high (1) or a low (0) to the bus, but the 0 can dominate a 1. I.E. If two transceivers try to speak at the same time, and one is saying 1 and the other is saying 0, then the 0 will win. We can re-create the same situation simply using diodes. Based on this appnote, TX and RX should be shorted. 

  • 0 in reply to QJ Wang
    Expert 1300 points

    Hi All,

    Do you means to say, without CAN transceivers, we cannot connect direcly connect CAN port of 2 microcontrollers channel??

    Regards,

    S.Saravanakumar

  • 0 in reply to Saravanakumar S93
    TI__Guru**** 197596 points

    No, two CAN controllers' pins should not be connected directly (TX-RX).

    When a CAN node is transmitting it is also reading back the current bus state to make sure the bus state is what it is transmitting (Bit 0/1 error occurs if doesn't match), and the CAN frame can get ACKed (acknowledged). If you connected the two pins together (TX--RX) the transmitting CAN node would never see a change in the bus state and transmission would fail (CAN bus off, and bit 0 error).