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STM32F103: noise on GPIO input signal causes weird behaviour

Question asked by almar on Feb 11, 2015
Latest reply on Feb 13, 2015 by Danish Ali
Hi everybody,
I am struggling against a weird behaviour on a input GPIO.
The GPIO input circuit is a simple pull-up; due to other components connected to my board, there is sometime some noise injected into the GPIO input line. The GPIO input voltage is normally about 3.3 V (as i mentioned above, input ciruit is a simple pull-up), when the noise is injected, the input oscillates between  3.3Vto 0V for about 20 usec (measured with oscilloscope). 
If I run a really simple application where the main function is just a loop where I read the gpio input value and set the read value to a output gpio, what I see is that sometimes when I inject noise in the input gpio, the output gpio stays low for about 500 ms (!!) even if the input signal is already high (the noise only lasts 20 usec..).
The only explanation I could give is that the gpio internal schmitt trigger keeps the internal value low... but of course it is hard to explain why.
Did you ever encounter similar problems?
Thank you!