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CAN CHIP QUERY

VIKRAM ROY CHOWDHURY
Prodigy 70 points
Other Parts Discussed in Thread: TMS320F28379D, SN65HVD233, SN65HVD234

Hello

     My name is Vikram and I have a tms320f28379D docking station. I am trying to get CAN communication and have connected transceiver chip of SN65HVD233DR in my breakout board. First, I am little confused that in this chip I have something called an LBK port which is for loopback. Since I do not have any loopback I have grounded it. Is it correct? Then I have RS and for high speed mode I have also grounded it. Then CAN L and CAN H are terminated on a 120 ohm resistor. Then I am trying to connect this CAN L and CAN H on a TMS320f28379D launchpad that has SN65HVD234DR transceiver chip.

The issue I have is when I use my code and use two launchpads I can successfully accomplish CAN communication as expected from my code application. But with a docking station and launchpad I do not see any CAN communication. What can be the possible reason? Can it be that docking station breakout board has SN65HVD233DR and launchpad has SN65HVD234DR that is why they are not communicating. I am actually pretty new to CAN so I am unsure how to fix this.

Can anyone kindly help me to solve this issue.

Thank you in advance.

  • 0
    TI__Guru 74282 points

    Vikram,

    First, your configuration for normal operation of the SN65HVD233 is correct, grounding the LBK pin will disable the loopback function, and grounding Rs will place the device in high-speed mode, meaning CAN communication will be active.

    When you say you do not see any CAN communication, do you mean on the RXD pin, the CANH/CANL pins, or both? The SN65HVD234 and SN65HVD233 should be able to communicate with each other since they are from the same family of devices, and even so both devices should be able to communicate with any CAN transceiver. Is it possible to also share a schematic? And have you captured any waveforms of CAN communication that can be shared?

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 70 points

    Thank you for your reply. I was still trying several things it did not work. My schematic is attached with this text. I used a can ex 2 code from C2000 ware and saw pulses on the GPIO pin every 1 sec which on the can h and can L bus showed nothing. Also I came to know that in an idle mode with the 3v3 the CAN H and CAN L should be at a bias dc voltage I also do not see that. Does it mean my chip is gone? Also, in the attached schematic do you find anything wrong in terms of connection for the application mentioned in the schematic.

    Kindly let me know.

    Thank you in advance.

  • 0 in reply to VIKRAM ROY CHOWDHURY
    TI__Guru 74282 points

    Vikram,

    Your overall bus impedance is 30 ohms which is too low for the CAN driver to properly drive CAN messages. Replace both 60 ohms with 120 ohms to give an overall bus impedance of 60 ohms, and let me know if this helps.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 70 points

    Thank you for your reply. I have a very small query can you kindly let me know if there are anywhere in North America the stock of SN65HVD233DR CAN chips as it seems out of stock everywhere. 
    Thank you again for thr suggestion and I am trying to take of one 60 ohm on each side as I have 2 120 ohm in parallel that will make the overall 60 ohm

  • 0 in reply to VIKRAM ROY CHOWDHURY
    Prodigy 70 points

    Hello I tried with that and seems to work. Thank you first, second I have a little query. Now we have a SN65HVD232D CAN chip where the LBK, RS, pins are not there but have NC or no connection. My query is since the footprint is the same if the NC in SN65HVD232D is grounded i.e. we solder this chip on the same PCB for the SN65HVD233DR will that work as the only change that we are doing is to put the NC's to GND.

    Kindly suggest and let me know your thoughts.

    Thank you in advance.

  • 0 in reply to VIKRAM ROY CHOWDHURY
    TI__Guru 74282 points

    Vikram,

    I'd recommend reaching out directly to our marketing team at trx_mkt@list.ti.com about device supply and availability. I'm not sure where units for SN65HVD233DR can be found online.

    And yes, placing the SN65HVD232DR in place of the SN65HVD233DR will work. The NC pins are true no connects and no connection to the die internal to the IC, so grounding them will have no effect on device function.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 70 points

    Thank you for letting me know. We are going to try to use this IC for the work and post the finding soon.