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 GUID-05CAE4DB-751B-4826-9CD0-5292B3842460.html#GUID-05CAE4DB-751B-4826-9CD0-5292B3842460.

Unused inputs must be terminated to either V_CC or ground. These can be directly terminated if the input is completely unused, or they can be connected with a pull-up or pull-down resistor if the input is to be used sometimes, but not always. A pull-up resistor is used for a default state of HIGH, and a pull-down resistor is used for a default state of LOW. The resistor size is limited by drive current of the controller, leakage current into the CD74HC14, as specified in the GUID-941836DA-3BC3-482C-98B8-9A7D6C596A61.html#GUID-941836DA-3BC3-482C-98B8-9A7D6C596A61, and the desired input transition rate. A 10-kΩ resistor value is often used due to these factors.

The CD74HC14 has no input signal transition rate requirements because it 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 GUID-941836DA-3BC3-482C-98B8-9A7D6C596A61.html#GUID-941836DA-3BC3-482C-98B8-9A7D6C596A61. This hysteresis value will provide 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 GUID-670A4F57-EBD6-4EDC-8B46-9C6061F38800.html#GUID-670A4F57-EBD6-4EDC-8B46-9C6061F38800.

Refer to the GUID-2343434F-FD22-40B7-AE6F-ABC1B329BA09.html#GUID-2343434F-FD22-40B7-AE6F-ABC1B329BA09 for additional information regarding the inputs for this device.