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ISOW1432: ISOW1432DFMR

Gulbahar G.
Prodigy 70 points
Part Number: ISOW1432

I designed this circuit. But modbus didn't work with 1200 metres.

Can you check the this circuit?

  • 0
    TI__Guru 55405 points

    Hi Gulbahar,

    Thank you for reaching out and sharing the schematic. I have reviewed the schematic and it looks good.

    Regarding communication issue, could you please let me know what datarate did you try to run when the cable length was 1200m?
    Typically, the maximum datarate supported with 1200m cable length is 200kpbs. This is provided as a guideline by the RS-485 standard. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 70 points

    Hi Rao,

    Our datarate is 9600 bps. 

  • 0 in reply to Gulbahar G.
    TI__Guru 55405 points

    Hi Gulbahar,

    Thank you for confirming the datarate as 9600bps.
    The device should support 9600bps for a cable length of 1200m although this isn't necessarily a common use-case.

    1. Could you please confirm what kind of issue are you facing?
    2. How many nodes are there on the bus?
    3. Can you please share the waveform at RS-485 bus pins?
    4. Please also share the PCB layout to review.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 70 points

    1-No communication with the card at 1200 meters

    2- We don't know.

  • 0 in reply to Gulbahar G.
    TI__Guru 55405 points

    Hi Gulbahar,

    Thank you for sharing the PCB layout files. The PCB layout looks good and I don't see any major concerns with it.

    I understand that there is no communication when the cable with 1200m length is added. To rule out software or other related issues, could you please capture waveforms at the input (TXD) and output (Y/Z) of ISOW1432? Without waveform, it is difficult determine the cause.

    I am assuming that you are performing these tests in lab and you have access to both ends of the 1200m cable. If this is the case, please provide waveform at the far end of the cable as well.

    It is also important to know the number nodes connected on the bus during test and if the bus was terminated correctly at both the opposite ends of the bus. Please confirm this, thanks.


    Regards,
    Koteshwar Rao