[FAQ] How do I terminate any unused channels of a logic device?

FAQ: Logic and Voltage Translation > Input Parameters >> Current FAQ

CMOS Inputs

All CMOS inputs must be terminated at either Vcc or Ground.

The inputs of a CMOS device are high-impedance.  These terminations can be through a resistor (for example, a 10kohm pull-up resistor to Vcc or a 1kohm pull-down resistor to ground), or they can be directly connected. 

CMOS Outputs

CMOS outputs are typically best left floating. 

CMOS I/O Pins

In transceivers (where inputs and outputs share a pin), the output can be terminated to ground or Vcc through a resistor (10k, 100k, etc).