Dear Mr. Cobb,

you could look into the data books from different CMOS gate manufacturers.
They always recommend, ( you should ! ), to terminate the inputs of the CMOS
gate.
Cause of the high impedance of this series, the input level can float between
the trigger point
of the gate. The gate now may oscillate and influence other gates in the same
device.
This effect depends from the chip structure and the power supply.
Consider also EMI effects, which can damage in some cases high impedance
inputs.
In my early developer years i have seen such effects.
So always tie CMOS inputs of the CD/HCF series to VDD or VSS.

Peter Schoepe
( Elektronik-Service Schoepe )

Nicholas Cobb wrote:

> In a post about a month ago Mr. Lomax mentioned that leaving a CMOS input
> open could cause problems on a board.  Are there any references that will
> help me learn the details that might cause problems like this in commercial
> devices?  Up to this point I have been making circuit boards that will be
> used only by me.  I am just starting to work on some that will be mass
> produced.  Any sort of help would be appreciated.
> Thank you,
> Nick Cobb

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