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Modbus/RS485 hardware connection for TMDSCNCD28069MISO

Maria Todorova
Guru 13185 points
Other Parts Discussed in Thread: TMDSHVMTRINSPIN, MAX232

Hello all,
I want to have Modbus/RS485 communication from F28069m to PC.
I am using TMDSHVMTRINSPIN and TMDSCNCD28069MISO.
I have USB-to-RS485 Converter connected to my PC.

1. What is the way to connect this converter to my device (TMDSHVMTRINSPIN and TMDSCNCD28069MISO)?
I tried to connect directly TX and RX (GPIO29 and GPIO28) and GPIO42 as TXEN to SP485, and then the output A and /B from SP485 to  A and /B of USB-to-RS485 Converter, but the receive interrupt has never occurred when PC (my Modbus software, also Hyperterminal) sent message.
Briefly, the connection is like the figure below.



When I used COM port from FTDI of TMDSHVMTRINSPIN, the receiver interrupt occured and the results were fine (I could see input registers in my Modbus software in PC when I sent Modbus command Read Input Registers).



2. Actually, is it possible to connect TX and RX (GPIO28 and GPIO29) from TMDSCNCD28069MISO to have communication with USB-to-RS485 Converter?
Or

is it because GPIO28 and GPIO29 are already connected to FTDI of TMDSHVMTRINSPIN, so it can not be used for this purpose, and I need to connect SP485 to another pins?

Or

Is the hardware connection wrong?

However, I used similar connection for another microcontroler (not TI) and it worked well so I don't know what the difference is in TI microcontroller.

I also have checked USB-to-RS485 Converter with another device and it worked well.


Thank you in advanced!


Best regards,
Maria

  • 0
    Guru 20525 points

    Hi Maria!

    I'm not sure, but perhaps you need MAX232 (level converter TIA/EIA-232-F to TTL/CMOS) between GPIOs & SP485.

    Regards,

    Igor

  • 0 in reply to Igor Gorbachev
    Guru 13185 points

    Hi Igor,

    Thanks for the response.

    Maybe you are right. I will try it today and let see whether this works (at least to get any interrupt).

    Best regards,

    Maria

  • 0 in reply to Maria Todorova
    Guru 20525 points

    Hi Maria!

    Let me please to know your results.

    Good luck,

    Igor

  • 0 in reply to Igor Gorbachev
    Guru 13185 points

    Hello Igor, and all,

    I already have the answer of my own question.

    About MAX232, I connected GPIO28 (RX) and GPIO29 (TX) to MAX232 and connected it directly to DB9, and no communication was appeared.

    However, I connected GPIO19 (RX) and GPIO18 (TX) to MAX232 and connected it directly to DB9, and there was communication.

    So unfortunately for GPIO28 and GPIO29, I could not connect it as another COM except the COM from FTDI of the kit. For the reason, I am not sure.

    I then used GPIO19 and GPIO18 and connected SP485 just like the figure I mentioned before and everything went well.

    Thanks for all attention.

    Have nice days!

    Best regards,

    Maria

  • 0 in reply to Maria Todorova
    Guru 13185 points

    Another thing in my mind.

    If I only have GPIO28 and GPIO29 (SCIA) that are already connected to FTDI by default, can I use them for this communication?

    Based on ChrisClearman said in this thread

    http://e2e.ti.com/support/microcontrollers/c2000/f/171/t/273886.aspx?pi269061=2

    TMDSCNCD28069MISO is the only ControlCard that has the contention so I hope this is not general problem.

    I have no other type of ControlCard to try so if somebody has experience to connect GPIO28 and GPIO29 (SCIA) that already connected to FTDI in the kit and still can use them as another COM without using this FTDI, please share it.

    Thank you.