Unused IC legs. Gound or to Power.

[MrWild]

Last time I picked up a book on circuit design it stated to ground or put all unused lkegs to power. VCC I think the term was. I balked at this information because I am unsure what it means. Won't short circuits happen? Don't I need to know what polarity will keep the chip from frying? If I take this literally, it don't matter to which they go, but they have to go to something. Can they be mixed? Half power, half ground, or all need to be ground or all to power. This one design rule has me confused as to what it means exactly.

[Al_The_Man]

Generally the input to a digital IC is normally either a 1 or 0 (+v or com).
The idea of connecting the unused input to either is to avoid spurious noise being picked up by a high impedance input and causing problems to any internal processing.
Tying the input to either causes no harm to the IC.
The impedance is high enough that no harmfull current flows.
Al.

[Rube]

Originally Posted by MrWild ...ground or put all unused lkegs to power...

as mentioned above, it is only unused INPUTS that get grounded or pulled up. and yes you can mix some UNUSED INPUTS pulled up and some UNUSED INPUTS grounded.

[MrWild]

Originally Posted by Rube as mentioned above, it is only unused INPUTS that get grounded or pulled up. and yes you can mix some UNUSED INPUTS pulled up and some UNUSED INPUTS grounded.

THANKS. Ankd froml this I can assume unused outputs are left completely unconnected. This explains a LOT. The book didn't state inputs... Hmmm, I better dig out that part and see if it did. I was thinking all unused legs when I read it. It may have said inputs, but you know how the mind works.

[Rube]

Originally Posted by MrWild ...you know how the mind works.

or doesn't sometimes...LOL yeah I know exactly what you mean. yes unused outputs stay floating. and another thing, this is typically on DIGITAL logic chips (and even some of those have internal pull up/down) or your typical op-amp circuits (but on those you tie one of the two inputs to the output, and the other input to ground or Vcc). data sheets should be thoroughly examined for details if you are working with a chip you are unfamiliar with.