All inputs of the C16x family have Schmitt-Trigger input characteristics. These Schmitt-Triggers are intended to always provide proper internal low and high levels, even if an undefined voltage level (between TTL-VIL and TTL-VIH) is externally applied to the pin.The hysteresis of these inputs, however, is very small, and can not be properly used in an application to suppress signal noise, and to shape slow rising/falling input transitions. All inputs of the C16x family have Schmitt-Trigger input characteristics. 1 Input Signal Rise and Fall Times 3