Unused Input

Input

Output

Input

Unused Input

Output

SN54HC74, SN74HC74

www.ti.com

SCLS094E – DECEMBER 1982 – REVISED DECEMBER 2015

11 Layout

11.1 Layout Guidelines

When using multiple bit logic devices, inputs should not float. In many cases, functions or parts of functions of

digital logic devices are unused. Some examples are when only two inputs of a triple-input AND gate are used,

or when only 3 of the 4-buffer gates are used. Such input pins should not be left unconnected because the

undefined voltages at the outside connections result in undefined operational states.

Specified in Figure 6 are rules that must be observed under all circumstances. 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 must be

applied to any particular unused input depends on the function of the device. Generally they are tied to GND or

transceiver. If the transceiver has an output enable pin, it disables the output section of the part when asserted.

This pin keeps the input section of the I/Os from being disabled and floated.

11.2 Layout Example

Figure 6. Layout Diagram

Copyright © 1982–2015, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: SN54HC74 SN74HC74