AnsweredAssumed Answered

STM32F4 Resetting itself (Nucleo 64)

Question asked by Andres Cao on Apr 14, 2017
Latest reply on Mar 8, 2018 by Mark Peter Vargha



I have a Nucleo64-446RE and every 5/10 minutes the board resets itself.


I'm using the Virtual COM to send data to my PC and plot it (among many other things), and when the board resets I lose the Serial connection. I need to re-open it in order to plot again. If after this reset I want to program the microcontroller I get the "Unable to reset target" message for which I need to unplug and replug the USB(which is also powering the board). I'm using the System Workbench for STM32.


Here's an oscilloscope picture of the NRST pin (blue), which confirms the reset. The red trace is a 3.3V pin, which shows there are no power issues. 


Can you please help me debug this reset?


As I understand, it can't be a Hard Fault because (I think) in that case the system wouldn't reset but end up in an infinite loop. I haven't implemented any of the error handlers, but I think they're implemented by default with weak attributes.


Watching the following image:


From external sources:

  • Definitely I'm not pressing the reset button
  • The ST-LINK could be resetting. How likely is this, why would it? Given that Virtual Com connection is lost it could be the case, since if I press the reset button the Virtual Com connection is not lost.


From internal sources:

  • WWDG is not activated
  • IWDG is not activated
  • Red trace would prove it's not a power reset
  • There's no lower-power mode being used.
  • Software reset, this would be the only option. What causes a software reset?


Thank you very much in advance for all your input!