Input signals must cross V_t-(min) to be considered a logic LOW, and V_t+(max) to be considered a logic HIGH. Do not exceed the maximum input voltage range found in the Absolute Maximum Ratings.

Unused inputs must be terminated to either V_CC or ground. These can be directly terminated if the input is completely unused, or the input can be connected with a pullup or pulldown resistor if the input is to be used sometimes, but not always. A pullup resistor is used for a default state of HIGH, and a pulldown resistor is used for a default state of LOW. The resistor size is limited by drive current of the controller, leakage current into the SN74HCS266, as specified in the Section 5.5, and the desired input transition rate. A 10kΩ resistor value is often used due to these factors.

The SN74HCS266 has no input signal transition rate requirements because device has Schmitt-trigger inputs.

Another benefit to having Schmitt-trigger inputs is the ability to reject noise. Noise with a large enough amplitude can still cause issues. To know how much noise is too much, please refer to the ΔV_T(min) in the Section 5.5. This hysteresis value provides the peak-to-peak limit.

Unlike what happens with standard CMOS inputs, Schmitt-trigger inputs can be held at any valid value without causing huge increases in power consumption. The typical additional current caused by holding an input at a value other than V_CC or ground is plotted in the Typical Characteristics.

Refer to the Feature Description for additional information regarding the inputs for this device.