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GPIO noise on power ON

Question asked by arnogir on Jun 13, 2017
Latest reply on Aug 24, 2017 by arnogir



I'm using a Kinetis K70 with MQX 4.1, KDS 3.2 and a debugger P&E micro Multilink universal.


My software is composed by many task; but only one in "AUTO_START"

The very fist instruction in this task ("Main_Task") is to configure a GPIO as an output with default level 0.


static void Main_task(uint32_t InitialData)
  LWGPIO_STRUCT   TestHandle;

  lwgpio_set_functionality(&TestHandle, LWGPIO_MUX_A26_GPIO);


So in debug mode (step by step) this output pin value is always 0, and then toggle to 1 with the last two instruction.


But when the board start in standalone mode (without probe p&E micro Multilink universal), the output pin value goes to a level 1 during 10ms. After that, Is see the pin goes low and then toggle to 1 -> 0 with my init code.


Conclusion: between the CPU start (after power on) and until the first code line executed in the main_task, there passed 10ms with a pin to an unexpected state (high level)


Is somebody has idea where look at to found the problem? My aim is to have an output pin which stay to Low level during the initialisation... THis is the case when I start with probe, but not when start in standalone... ???


Note: A pull-down resistance (4k7) is applied to this pin...