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SN65HVD230: SN65HVD230

deepblue
Prodigy 30 points
Part Number: SN65HVD230
Hello all I am using the sn65hvd230 (this board Waveshare SN65HVD230 Can Board Connecting MCUs to Can Network Features ESD Protection Communication Evaluation Development Board 3.3V www.amazon.fr/.../ref=cm_sw_r_cp_tai_cxbaEbFVNZX01 ) I am a noob in electronics I am a software dev. This problem is easy to describe, Résistances between can H and can L is lowered as long as I had nodes I have a system with 12 nodes, I read that resistance between can L and can H is like: 50>Value>70. With one node, I have 60 ohm. With two nodes I have 40 ohm
  • 0
    TI__Guru 60242 points

    Deepblue,

    Thanks for bringing this question to us. I can't be totally sure because I haven't seen a schematic, but looking at the pictures of the board, it looks like there is a resistor connected between CANH and CANL on the board. In CAN systems, the termination impedance is meant to be 60 ohms, generated by two 120 ohm resistors in parallel at the end nodes of the CAN bus. If more nodes are added to the CAN bus, depending on the physical length of the connection, higher resistance termination can be added or left off. The reason the resistances are higher for nodes that aren't the end nodes is so that they don't take away too much from the termination impedance of 60 ohms when added in parallel. I'm guess whatever you're connecting to also has a 120 ohm resistor in place.

    What is happening here is there there is a 120 ohm resistor between CANH and CANL, so as you connect these boards to the bus, these resistors keep getting added up in parallel. So when you add one, then both 120 ohms become 60, then adding one more (three 120 ohm resistors in parallel) you get 40 ohms. What you can do is once you've connected the first board, you can then remove the resistors between CANH and CANL on all of the other boards that are added. 

    I know there's a lot of information here but I tried to give the necessary information so you can understand exactly what is happening and why. Please let me know if you have any other questions or concerns.

    Regards,

  • 0 in reply to Eric Hackett
    Prodigy 30 points
    Éric, Thx a LOT Your response is very clear. So, basically, I have to put a shunt between each 120 ohm resistor. I will try that ! Here is a photo of what I try to achieve: www.instagram.com/.../ I will post here when I have news ! Tomorrow morning I hope. Thx you again.
  • 0 in reply to deepblue
    Prodigy 30 points

    Eric,

    that worked perfectly. All 12 nodes are now speaking !

    I simply removed the 120 ohm (no shunt).

    Thx you again !