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EK-TM4C123GXL: USB uart with external supply

luca mattonai
Intellectual 690 points
Part Number: EK-TM4C123GXL

Hi, 

I have powered the EK throught the target USB, the burned application starts and work but the USB port of debugger is enumerated but  doesn't works.

Any suggestion?

Best regards 

  • 0
    TI__Guru 72500 points

    I am able to power my EK_TM4C123GXL through the target USB connector (the connector on the side) with the power switch in the "Device" position (to the left). I have a second USB cable connected to the debug port (on the top). I am able to debug using Code Composer Studio and I am able to use the virtual serial port. Can you provide some more details so that I may attempt to duplicate your issue?

  • 0
    Intellectual 690 points

    Hi Bob

    Some more detail...

    I have powered the EK not using the target USB connector but using a DC/DC converter connected to the VBUS pin of the header connector then I have put the switch in target position.

    In this situation if I connect the USB (debug) to the PC and after I power the EK the VCOM enumerate and works correctly, in this situation if I unplug and plug again the USB sometimes the VCOM enumerate but communication is not active.

    The application writes data packet at 10ms continously over the VCOM and I can see data on the Tx test point..

    Best Regards

  • +1 in reply to luca mattonai
    TI__Guru 72500 points

    I suspect the issue is that the ICDI chip which creates the virtual serial port needs to be reset when the debug USB connector is unplugged and then re-plugged. 

    Is there a reason that you power the launchpad this way? Can you cycle power on the external VBUS supply before attaching the debug USB cable?

  • 0 in reply to luca mattonai
    TI__Guru*** 135355 points

    Hello Luca,

    If I understand right about your use of VBUS then that would be a +5V signal. I would not power the LaunchPad from VBUS.

    See this app note on how to connect Host Mode for the EK-TM4C123GXL: https://www.ti.com/lit/pdf/spna243

    Best Regards,

    Ralph