I have just answered a question here, and it has spurred me to ask a question:

How fast will this type of protection work? Would it work with, say, a 500kHz signal?
(Using zener and resistive divider to protect from overvoltage)

I would expect, at some point, that oscillations would occur where the zener doesn't break down fast enough?


The previous question: https://electronics.stackexchange.com/questions/320159/12v-input-on-microcontroller-pin/

Schematic example given by Michael on that thread:
 
[![Example][1]][1]


  [1]: https://i.sstatic.net/Om0Vk.png