Hi Kawai-san,
There has been some confusion about this spec. The voltage on the inputs can be up to the maximum ratings.
The spec is intended to provide two pieces of information.
1) The device typically switches points from high to low and low to high at the typical values. This also shows some hysteresis.
2) The min Vil and max Vih show the values that the device will recognized a logic low (<= Vil min) and a logic high (>=Vih max). To make certain a logic high is accepted, the input voltage must be >= Vih max. To make certain a logic low is accepted, the input voltage must be <= Vil min. Between these values, the device may not have transitioned.
Think of the Vil spec as "Input logic-low voltage falling threshold" and the Vih spec as ""Input logic-high voltage rising threshold"
There has been some confusion about this spec. The voltage on the inputs can be up to the maximum ratings.
The spec is intended to provide two pieces of information.
1) The device typically switches points from high to low and low to high at the typical values. This also shows some hysteresis.
2) The min Vil and max Vih show the values that the device will recognized a logic low (<= Vil min) and a logic high (>=Vih max). To make certain a logic high is accepted, the input voltage must be >= Vih max. To make certain a logic low is accepted, the input voltage must be <= Vil min. Between these values, the device may not have transitioned.
Think of the Vil spec as "Input logic-low voltage falling threshold" and the Vih spec as ""Input logic-high voltage rising threshold"