EXTI Edge Detection Characteristic for STM32H7 - rise/fall time?

[NickO]

I am trying to detect both rising and falling edges on a GPIO input using EXTI.

I am using a STM32H755 (144 pin) - SYSCLK is 400MHz, but I am using the CM4 core, so the CPU clock is 200MHz. APB Timer clock is also 200MHz.

The signal I am monitoring is coupled through an opto-isolator, and having scoped it, seems to have a rise-time of approx. 5us. I am wondering if this is too slow for EXTI rising / falling edge detection?

I've been looking at both the datasheet and reference guide for the STM32H755 and I could not find any data on max and min rise times for edge detection to function reliably.

[RobK1]

The digital I/O pins have a Schmitt trigger input, as witnessed by this characteristic:

(Page 151 of the datasheet)

So rise- and fall times should be no issue.

[NickO]

Hi

 

Thanks for the response. We were discussing that in the office and could not see how beyond the Schmitt trigger, anything more complex is likely to be going on except some possible de-bounce logic. My guess is that beyond the Schmitt trigger, it simply detects a state transition and any de-bounce due to noise would be my problem to solve.

What has thrown this into doubt is "a certain AI tool", where it suggested (with great confidence) that edges had to transition within a few uS to be "reliably" detected. Who knows where this comes from, but it seeds uncertainty and suggests something more elaborate might be going on. I wonder if the AI is muddling responses related to very noisy signals? Who knows.

 

Many thanks again,