1-1. Handling of Unused Input Pins

Generally, all unused inputs should be tied to either V_CC or GND.
However, any pins of bidirectional bus buffers (e.g., Function 245) that can be configured as an output (e.g., bus pins) should be tied to V_CC via a pull-up resistor or to GND via a pull-down resistor. It is recommended that both ends of the buffer be pulled up or down to the same potential to avoid unnecessary current flow. However, leave the input pins with bushold, such as those of the ICs of the TC74VCXHxxx Series, open. Large inrush current due to parasitic capacitance (in the order of a few milliamperes) can be a problem even with typical CMOS logic ICs when their power supply is on. In order to improve system reliability against device destruction and other failures, their inputs can be tied to V_CC via a pull-up resistor or to GND via a pull-down resistor.

Because CMOS logic has a very high input impedance, any open input might result in a false output value due to the influence of a surrounding electric field. In addition, shoot-through current might flow at the midpoint of V_CC and GND, causing an increase in supply current and leading to device destruction in the worst-case scenario.
Be sure to apply these considerations to all inputs without a bushold capability unless otherwise instructed in the datasheet.