Hello kai,
Thank you for your reply,

Yes I agree with that but if I want to debounce a matrix keypad safely then as you suggested the debouncing time should be about 50ms. It means if a user presses a key his request will not be processed sooner than 50 ms (debouncing time).
Ok, that’s reasonable in theory because as I said earlier we have no perception of time less than 100 ms (I will try it experimentally to see if response is reasonably fast).
Now if I just set scanning rate to 50 ms without debouncing the results will be the same as I explained it earlier to our friend prahlad.

thank you very much