Are there any problems with the input pins of CMOS logic ICs and the bus pins (input/output pins) of bidirectional bus buffers in a floating state?

Do not leave unused input pins of CMOS logic IC floating and connect them to VCC or GND as shown in Fig. 1. In the floating state, unexpected output or oscillation may occur due to disturbance noise, etc.

The bus pins (I/O pins) of 74xxx245 and other bidirectional bus buffers are floating when /G pin is set to High. When /G pin is High, connect the bus/output pin to VCC or GND with a resistor as shown in Fig. 2.

In addition, do not apply an external signal when the bus pin is in output mode.
Products with a bus-hold function (such as 74VCXH) do not require an external pull-up or pull-down resistor.
Please refer to here for bus hold.
FAQ: What is bushold of the general-purpose logic ICs?

Fig. 1 Unused inputs of CMOS logic ICs tied to V<sub>CC</sub>
Fig. 1 Unused inputs of CMOS logic ICs tied to VCC
Fig. 2 Unused bidirectional pins of a bidirectional bus buffer pulled up to V<sub>CC</sub> or down to GND
Fig. 2 Unused bidirectional pins of a bidirectional bus buffer pulled up to VCC or down to GND

Related Links

The following documents also contain related information.

Product Lists

FAQs

Application Notes

Product page General Purpose Logic ICs
Products
e-Learning Basics of CMOS Logic ICs
e-Learning
e-Learning Usage Considerations of CMOS Logic ICs
e-Learning

Back to FAQs of General-Purpose Logic ICs

A new window will open