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SN65HVD30: SN65HVD30MDREP, Unable to use in Fullduplex and Half duplex mode

abhishek Kumar
Prodigy 90 points
Part Number: SN65HVD30


Hi TI Team,

We are using the RS485 transceiver IC part not SN65HVD30MDREP for RS485 communication.
We are facing the below issue while we are trying to communicate between two microcontroller.

Issue1- We are not getting any appropriate data while we are operating in full duplex mode.
We are using the below schematics, Kindly review and suggest your feedback.

Issue2- Shall we use this IC as a Hal duplex mode?
If yes , please suggest the changes in the schematic i.e. we can communicate between two controller via RS485 in Hal duplex mode.

We have followed some online reference, and trying to use the above transceiver as a half duplex. Please suggest ie it is OK or need any modifications.

Kindly suggest your valuable feedback.

  • 0
    TI__Mastermind 25705 points

    Hi,

    I'm sorry the schematic doesn't show in your post. Can you re-upload them as attachment? Other than the schematic, can you provide more system information, like the data rate, distance, grounding, etc? Thanks,

    Hao

  • 0 in reply to Hao L
    Prodigy 90 points

    HI Hao,

    Thanks for your reply.

    Please find the attached sheet for more details for issue.

    Data rate- 9600

    Distance- 2 meter

    Grounding- We are using all the slave devices interfaces with master along with fullduplex( 4 wire communication) , No common ground 

    Is common ground is needed for all the slave devices which are connected in multidrop.

    Please suggest with some ref schematic.

    Regards 

    Abhishek 

    RS485 issue in Full duplex and Half duplex.pdf

  • 0 in reply to abhishek Kumar
    TI__Mastermind 25705 points

    Abhishek,

    The schematic looks good to me. However please make sure the 5V diodes don't clamp the bus signal. The half duplex scheme should work too. A note is that please make the device 2's wire connection to the bus as short as possible.

    You can test the full duplex mode with loop back first.

    BTW, If Roland's post addresses the same issue, maybe we can merge the discussion into one thread.

    Regards,

    Hao

  • 0 in reply to Hao L
    Prodigy 90 points

    Hi Hao,

    Thanks for review the schematic, we have not checked the TVS diode for clamping the Bus signal.

    As it is mentioned in the datasheet section 10.2

    Link- in Datasheet Part no- SN65HVD30MDREP

    Please check the above comments and let me know ie it is the only issue or not.

    Due to that we are planning to use the different Part no - SN65HVD10QDREP 

    So we are updating the schematic as per below, Please review and let us know ie it is on or need any modification.

    Termination resistor is 100 Ohm as mentioned in datasheet.

     

    Yes, you can merge the Rolands post with this post.

    Kindly review and let us know your feedback on this.

    Regards

    Abhishek

  • 0 in reply to abhishek Kumar
    Prodigy 90 points

    Hi Hao, 

    Please find the attached documents for the issue, As the schematics is not bale to see in previous reply from my side.

    Regards 

    Abhishek RS485 issue with SN65HVD30MDREP.pdf

  • 0 in reply to abhishek Kumar
    TI__Mastermind 25705 points

    Abhishek,

    The schematic looks good. The termination resistance should match the cable impedance in your system, which could vary from 80Ohm to 150Ohm. If you wanted to add TVS diodes, SM712 is a common choice.

    Regards,

    Hao