When using multiple-bit logic devices, inputs should never float.

In many cases, functions or parts of functions of digital logic devices are unused, for example, when only six channels of an eight channel transceiver are used. Such input pins should not be left unconnected because the undefined voltages at the outside connections result in undefined operational states. All unused inputs of digital logic devices must be connected to a high or low bias to prevent them from floating. The logic level that should be applied to any particular unused input depends on the function of the device. Generally they are tied to GND or V_CC, whichever makes more sense or is more convenient.

The output enable pin disables the output section of the part when asserted. This does not disable the input section of the IOs, so they cannot float when disabled.

Figure 11-1 shows the proper method to terminate unused channels using a large resistance (in this example, 10-kΩ resistors). This avoids overloading the outputs , and maintains a valid voltage on the inputs. Note that it is also valid to tie both sides of an unused transceiver directly to ground or V_CC; however, the two sides must never be tied to different states directly.