From ESP32 datasheet:
In my case:
VDD = 3.3V
Vil (max) = 0.25 * 3.3 = 0.825V
Vih (min) = 0.75 * 3.3 = 2.475V
Theoretically:
LOW LEVEL range is -0.3V to 0.825V
HIGH LEVEL range is 2.475V to 3.6V
But when I tested practically:
LOW LEVEL range is 0V to 1.67V
HIGH LEVEL range is 1.67V to 3.3V
Question : Why is my practical range far different from the theoretical range and what does theoretical range from 0.825V to 2.475V mean?
Best Answer
The spec says that the input is guaranteed to be read as a Low below 0.25 Vdd, and as a High above 0.75 Vdd.
It does not specify where the actual switching threshold is - from the spec, we only know that the switching threshold is somewhere between 0.25 Vdd and 0.75 Vdd. The actual threshold may vary between parts or between pins on a given part. Possibly, the switching threshold will be higher for a Low to High transition, than for a High to Low transistion.