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SN65HVD08: Using SN65HVD08 with Modbus

Abhishek Sharma53
Prodigy 240 points
Part Number: SN65HVD08

Hi,

I am trying to use the part SN65HVD08 connecting to a Modbus slave on one side and the other to the USB-UART cable  https://www.digikey.ca/en/products/detail/ftdi-future-technology-devices-international-ltd/TTL-234X-5V/6823719.

Here I have implemented the Application circuit mentioned at the Page 19 of the datasheet of SN65HVD08 except the Direction control line connection .

I am using Modbus Scan simulator tool and I am not seeing any response here and it looks like everything else is correct. I sense here if the Direction line has to be controlled high and low.

I tried with pulling down the /RE and pulling up the DE at the same time to permanently enable the direction flow in both directions but looks like it does not work either. Does it has to do with the RTS and DTR setting of the connection setup in Modbus simulator tool ?

(The setup otherwise works good with MAX1387 based circuit where there is no direction control required)

Thanks

Abhishek

  • 0
    TI__Guru 62920 points

    Hi Abhishek,

    For a half-duplex connection (meaning the same wire pair is used alternatively to send and receive the data), proper control of the direction control lines (DE/RE) is critical.  You would need to make sure that the driver is enabled when it needs to send data on the bus and disabled when another node needs to transmit.

    Do you have a direction control line available in your system that could be used?

    If not, you may want to reference this thread to see how the DE/RE signals could be controlled automatically:

    https://e2e.ti.com/support/interface/f/138/t/830860

    Please let me know if you have any further questions.

    Regards,
    Max