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MSP-EXP432P401R: How to interface UART of above mentioned board with external bluetooth device

Mohan Gandhi Vinnakota
Prodigy 100 points

Part Number: MSP-EXP432P401R

Hi,

I would like to program an bluetooth device. I have MSP-EXP432P401R development board. This board has two parts debugger and MCU. 

I have taken out all jumper on J101. I have connected SWDIO and SWDCLK of bluetooth pins to SDWIO and SDWCLK of debugger part on J101. This works fine. I am able to debug the code. Bluetooth is working fine.

For my next step I would like to have serial communication between PC and Bluetooth. Now I have connected RXD and TXD pins of Bluetooth to TXD and RXD pins of debugger part. Also SWD pins also connected.

Here Im getting RDDI DAP eror on my keil5.

Im not able to understand why. If i disconnect the RXD and TXD pins (only SWD pins connected). It is working fine. The serial communication UART pins are making the difference?. What is the reason? and how can I do this communication?. Thank you.

  • 0
    TI__Guru 53585 points
    I agree that the TXD and RXD lines should not make a difference. Can you please confirm that transmits from both the XDS110 and the bluetooth part are not connected? If one is trying to drive high while the other is driving low, this could potentially hang the XDS110/JTAG communication. Also, can you confirm how power is being delivered to the Bluetooth device relative to the XDS110 on the launchpad?

    Regards,
    Chris
  • 0 in reply to Chris Sterzik
    Prodigy 100 points
    Hi Chris,
    Thank you for your feedback.

    Can you please confirm that transmits from both the XDS110 and the bluetooth part are not connected?

    No. They are not connected. Im unable to download the firmware to the RAM of bluetooth due to that error. Here I have connected the RXD pin of XDS110 to TXD pin of Bluetooth and TXD pin of XDS110 to RTX pin of Bluetooth.

    If one is trying to drive high while the other is driving low, this could potentially hang the XDS110/JTAG communication.

    Can you tell me how to do find that.

    Also, can you confirm how power is being delivered to the Bluetooth device relative to the XDS110 on the launchpad?

    Yes the power supply to bluetooth is supplied from XDS110 on the launchpad. It is 3v3 and GND pins of XDS110 on the launchpad.
  • 0 in reply to Mohan Gandhi Vinnakota
    TI__Guru 53585 points
    Hello,
    Keep in mind that the RXD and TXD on the launchpad silkscreen are with respect to the target MCU which is the MSP. RXD should be connected to the RX pin of the Bluetooth device and TXD to the transmit pin of the Bluetooth device.

    Regards,
    Chris
  • 0 in reply to Chris Sterzik
    Prodigy 100 points

    Dear Chris,

    Still I see the same problem. I have changed the connections as you suggested. I have connected RXD to Rx and TXD to Tx. No change. I see same error. If i disconnect both RXD and TXD then no error and im able to debug. I wanted to have some serial communication. Whenever I connect the RXD and TXD no matter interchanged or connected to same pins. I see that RDDI DAP error. I not able to figure out the issue. 

    One question: Does UART has a separate ground pin. I have one Vcc and one Gnd which are connected on MSP bpard. Should I connect all other ground pins to gnd?.

  • 0 in reply to Mohan Gandhi Vinnakota
    TI__Guru 53585 points

    Hello,

        The UART does not have a separate ground.  If you are using the ground pin on the J101 header (debugger side) this will be sufficient.  Is it possible that the bluetooth device has a short on the UART pins?  Is there an issue if only the TXD line is connected?

    Regards,
    Chris

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