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Stellaris Launchpad LM4F120: Sending UART over PIN headers

André Schaller
Intellectual 580 points

Hi guys,

I need to automatically switch my Stellaris LM4F120 on and off. During each trial, data will be sent over UART. In the standard configuration the board gets power AND sends data over the same USB connection. This is not what I want, since after turning off the board the system (my terminal application on my pc) will detect that the previous device was unplugged, which leads to a lot of problems. So my question is, is it possible to have the UART output on one of the PIN headers?

Best regards,
Andre

  • 0
    Guru 86745 points

    Hi Andre,

         Yes. Refer, to the LM4F120 Launchpad User's Manual. 

    -kel

  • 0 in reply to Markel Robregado
    Guru 117855 points

    Friend Kel's (now frequent) tendency to answer solely w/"refer to UM" fails to fully satisfy.

    Your quest to "route UART signals" to board's pin headers raises questions:

    a) will your connection to the PC be via USB or via older, RS232 port? 

    b) if via an RS232 port - might that prove advantageous when your MCU board is powered down?  (we've noted that our PC connection - via RS232 - stays "alive/well" when we kill MCU power - then later restore.}

    c) if you find an independent UART pair - routed to pin headers - you likely will have to CMOS-UART to USB or CMOS-UART to RS232 convert those signals.  Direct connection of the PC's RS232-TX to MCU's UART-RX - likely injurious to the MCU.  (thus - the need for the level shifter)

    d) if you are w/out RS232 port - and must convert from UART to USB - might the PC's USB management continue to "balk" when it detects loss of signal/power upon your MCU board? 

    Some things to consider - unlikely to be addressed via UM...

  • 0 in reply to cb1_mobile
    TI__Expert 3445 points

    Andre,

    In addition to the level-shifted UART to RS232 option described by cb1, you could also split the 3.3V power rail that powers the ICDI from the MCU_POWER rail that powers the MCU. You can do this by removing the VDD jumper from H24/25 on the board, and attaching an external power supply to H24.

    If the power to the ICDI is maintained, the serial connection will be maintained as well. Then, depending on your application, you can use the power supply attached to H24 to turn the MCU on and off.

  • 0 in reply to Stellaris John
    Guru 117855 points

    @Stellaris John,

    Believe yours to be good/solid alternative - provided, "power-down" is not indicative of, "battery operation" of poster's MCU board.  (doubt that the ICDI MCU can "maintain USB contact" if switched into a lower power mode - or that such switching to lower power was even considered in the ICDI MCU design/development)