This is a general question for all MCUs, but the answer probably differs based on the specific brand and architecture. I'm using a STM32F4 and I have a noisy interrupt signal, so I'm getting a lot of unintended triggered interrupts. I predicted this might be an issue so I designed the board with pads for a low-pass filter. Right now I'm trying to figure out what RC combination to use to bring the noise spikes down to a level that doesn't trigger the ISR. Of course I don't want too strong of a filter because I lose edge timing accuracy.
So my question is what constitutes a valid edges, rising or falling, to trigger an interrupt? Does it have to change from the valid TTL low/high levels (0.8V and 2V in my case), valid CMOS levels (1V and 2.3V in my case) or is there some other threshold? I can't find anything in the datasheets, so I don't know if I'm not using the correct terminology.