From the Microchip spec sheet section 27.8, a Schmitt trigger buffer has a max input low voltage = 0.2 VDD
That means anything below 0.2 VDD is guaranteed to be treated as a low.
and a min input high voltage = 0.8 VDD. For VDD = 5V
That means anything higher than 0.8 VDD is guaranteed to be treated as a high.
Anything in between 0.2 VDD and 0.8VDD is in the "transition region" and might be a high or a low.
That is how digital inputs are always defined.
for my circuit, the transition from high to low is happening somewhere between 1 and 4 Volts, not <= 1V as expected.
That is precisely as expected.
If you expected it to switch from low to high at 1V, what did you expect to happen at 4V?
Yes, a Schmitt trigger has a small amount of hysteresis (internal positive feed back), so the rising transition is at a slightly higher voltage than the falling transition to avoid oscillation at the transition point, but that's not the two limits we are talking about here.
post edited by qhb - 2019/04/05 16:46:02