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Question regarding Beaglebone black system reset pin state

David Chance
Genius 4775 points

I am trying to monitor the System_reset pin on the beaglebone black (Rev C) expansion header to determine when I can use the gpio pins of the beaglebone black.  When the beaglebone black is powered up the voltage is 3.3V, but after pressing the power_button the beaglebone shuts down and the voltage on the system_reset pin only drops to 1.2V.  This is not a low so I cannot tell when the system shuts down.  On my previous version of beaglebone the voltage dropped to 0V.  Is there a problem with my current device?

  • 0
    TI__Mastermind 30365 points
    David,

    On my BBB rev C, had a multimeter connected to pin 10 (SYS_RESET) of P9 and saw ~3V when the board is powered. If you hold the POWER button for about 8s, the board resets and the voltage on this pin dropped to ~0V. Not sure why your board is exhibiting otherwise. Do you have any other hardware connected to the board that you can remove to help isolate?

    Lali
  • 0 in reply to Lalindra Jayatilleke
    Genius 4775 points

    I think it is caused by the serial port connecting to the micro, no communication but the logic 1 (default state) there

    Somehow this connection didn't have such effect on the previous version of BBB

  • 0 in reply to David Chance
    Prodigy 25 points

    The system reset or CPU reset is for forcing the system to reset. It is an input not an output. Hold it to ground to reset the board. If has a pull up voltage to keep the board from resetting when it is not held to ground.

    You set the state and the board obeys. Any apparent signal from the pin is incidental.