IRQ on a rising edge of an EXTI line sometimes does not come. On a falling edge it always comes.

[Tomasz Wozniak]

The MCU is STM32F401CB.

VDD is 3.3V.

A few buttons are connected to PA0 (configured as EXTI rising/falling interrupt).

When a button is pressed, the IRQ always comes.

When a button is released, the IRQ comes rarely, if at all.

There's a filtering cap and a pull-up (100k) at each button.

With the cap at 1nF, IRQ at the rising edge comes (sometimes more than once).

With the cap at 100nF, IRQ at the rising edge almost never comes.

I suspect it might be due to the voltage slope being too flat (large cap loading thru large resistor).

How do I verify this is the case?

Or maybe its something else?

Where do I find EXTI line IRQ electrical characteristics -- I looked in the TRM and the datasheet, only found the minimal pulse width required for the IRQ to be triggered.

Thanks in advance

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Tomasz Wozniak