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3.3V Can transceiver and 5V Can transceiver on the same CAN BUS

Ali Acıoğlu
Prodigy 155 points
Other Parts Discussed in Thread: SN65HVD233, SN65HVD235

Hi All,

I have two nodes on the CANBUS.One of the nodes(listener) has Delfino(F28335) microcontroller used  transceiver as SN65HVD233 .The other node(talker) has 18f2550(microchip) used transceiver as MCP2551.I want to provide communication with each other.At first glance,I had a doubt about workability is MCP2551 works at  5V,SN65HVD233 at 3.3V.But the datasheet of the SN65HVD233 says they can operate with each other.

I set the circuit respect to figure 28 with some changes which left hand side is microhip node,the other side TI node.But I could not provide communication.By the way,there is no problem with microchip node it works fine with the other nodes made by microchip products. 

Please Can you tell me ,If I have a mistake about this communication which I miss? 

Note:  at  SN65HVD233,I did not use LBK pin if you want to know.I think it is OK.

Best Regards

Ali 

  • 0
    TI__Mastermind 20580 points

    4747.2012-11-02 CAN Transceiver 3V and 5V Mixed Network Basics.pdf

    3V CAN Trasnceviers are fully interoperable with 5V CAN trasnceviers.  CAN works on a differential voltages of the bus.  The HVD23x 3V CAN transceivers are widely used in mixed applications with 5V transceivers also on the CAN bus and they have passed the GIFT/ICT interoperability testing in this scenario as well.  Please see the attached PDF for the basics of this.  Without more information it is impossible to give further clues as to what is wrong in your case.  Are you sure you have the HVD233 in a mode where listening is possible, ie LBK must be pulled low, there is a weak internal pull down so if you left it floating in most cases it would be low but make sure that is the case.  If you are trying to transmist with the HVD233 you also need to make sure the Rs pin resistance is configured such that your loop time is fast enough.  Start with 0 ohm to GND to make sure you are in high speed mode.  Since the comment "could not provide communication" is very vague I cannot help more at this point if your issue is on the CAN bus (physical layer side) or the protocol (DSP/MCU side).  If you have some scope shots of TXD, RXD, CANH/CANL (as a diff pair) across the HVD233 and the other transceivers we can take a look at it and hopefully see where the communication is breaking down.

    -- Scott

  • 0 in reply to Scott Monroe
    Prodigy 155 points

    Hi Scott,

    Thank you for your reply,I know it was late but I read when you wrote at that day this reply.In a first glance,I had a doubt about at voltage levels.When you said this,I focused on the my software and I found the problem about the code and fixed it.Thank you there is no doubt anymore.

    Ali

  • 0 in reply to Ali Acıoğlu
    Prodigy 30 points
    Hi,
    I aslo have this problem.
    I'm using 2 nodes on BUS, the one is Dspic30F4011 used MCP2551(5V) as transceiver and the other is TMS F28335 used SN65HVD235 (3.3V) as transceiver. The problem is, they can't communicate with each other.
    Could you tell me how to fix it? Thanks!
  • 0 in reply to Tam Luong
    TI__Guru 62910 points
    Hi Tam,

    I'd recommend looking at the D, R, CANH, and CANL signals at both nodes on an oscilloscope to verify that everything is operating as you expect. This will help narrow down what is going wrong (e.g., issues with the physical signaling on the bus, issues with software, etc.). One other quick thing to verify is that the bus is properly terminated using two 120-Ohm resistors between CANH and CANL. The differential loading these resistors create is necessary for the CAN signal to quickly reach the "recessive" state.

    Regards,
    Max
  • 0 in reply to Tam Luong
    TI__Intellectual 2855 points
    Hi Tam,

    You may also refer to below Application note, it demonstrates the interoperability of 3.3V and 5V CAN transceivers.

    www.ti.com/.../slla337.pdf


    Regards
    TejasH
  • 0 in reply to Tejas Hommaradi
    Prodigy 30 points
    Your document is very useful .Thank you!