how much trigger voltages for STM32F103 rising falling edge triggered interrupts are?

[EYang.11]

Hi guys,

I'm a little confused about the trigger voltage for rising-falling triggered interrupts. As my previous understanding, the trigger voltage should be Vih and Vil. But some one told me Vih and Vil is not for edge triggered interrupts. The thing is, when I observe the waveform with a Oscilloscope along with an interrupt counter from Keil, I did see the interrupt happened when the voltage did not reach the Vih(rising edge). I use 3.3V voltage. The signal is only 1V around and the interrupts was triggered. I checked the manual of STM32 and did not find the answer.

Could some one help?

Thanks,

[KnarfB · Accepted solution]

The data sheet gives you a formula for max. VIL and min. VIH voltages. At some voltage between these values, the Schmitt trigger will switch from 0 to 1, and, with some hysteresis, from 1 to 0. These trip points will internally trigger the interrupt. The exact voltage is not specified and varies across chips. If you need a well-defined trigger point, you need to add a comparator.

[EYang.11]

Thanks for reply. I also find this 'undetermined' area in official doc. But my question is still there: why this area is undetermined? Related to what charactistics of hardware/circuit？Why could not design it as always determined?

[KnarfB]

Undetermined simply means: not specified in the data sheet. It is not a warranted product property. This allows a simple design within the digital domain and saves efforts in production testing and product qualification and increases the yield.

There are other STM32 MCU series like F3, G4, ... having analog comparators which might better suit your needs.

hth

KnarfB

[EYang.11]

Hi, thanks for reply. I thought the trigger value should be relatively close to the guaranteed value. For my case, I think the trigger value should be close to 2V instead of 1v. Will there be so big difference with the guaranteed value? My concern is there is some defect in our designed circuit that we do not notice yet.