What does hysteresis mean

[Adar70]

In a datasheet for STM32F303K8, page 77::

How does the Schmitt trigger hysteresis work here? When the input transitions from low to high, should the value of hysteresis be added to the minimum high level input voltage, or does it say that the pin will definitely remain low until the maximum low level input voltage plus hysteresis is surpassed? Or maybe somehow else? How am I supposed to take the hysteresis into account here?

[Andrew Neil]

 

[Adar70]

But the difference between V_IH and V_IL is bigger than 200mVfor 3,3V V_DD. So where is that 200mV loop placed at? In the undefned area perhaps? And your diagram doesn't make sense. Low V_IN gives high output level? No.

Maybe it's how this picture shows?