simple question about floating pins

[LaTech]

i am using a pic for a school project. The pic I
m using is an overkill. I have about 8 pins not used. The code works fine when I run it, but I recall someone here saying I should never leave the pins floating.

So I should use a 10k pull down resistor and pull all the unused pins to ground?

Thanks

[SherpaDoug]

That will certainly work. Often people have a fixed PCB with no room for resistors. Then I tell then to make the pins outputs.
The reason not to leave pins open is at least twofold:
1) If the pin decides to sit halfway between 0 and 1 it can cause the input buffer to draw lots of current or oscillate, which consumes power, generates heat, and if oscillating, generates electrical noise.
2) Floating pins are more susceptable to static damage. This is likely only to damage the pin involved, but may also hurt other circuits on the chip.
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[Mark]

http://www.ccsinfo.com/forum/viewtopic.php?t=3861&highlight=unused+pins

[LaTech]

Yep that answered the question, I did a search before i posted but the term 'floating' retrieved alot of number problems not pin problems.

Thanks again!

[guest2]

Hi,

Maybe you should configure them as inputs instead, if you connect the output to ground inadvertently then you might short the +5 V line.

thanks
arun

[Mark]

[dyeatman]

FWIW, I agree with Mark.

As a matter of practice I NEVER EVER connect any I/O pins (even ones normally A/D) directly to +V or ground... If something happens, regardless of how inadvertantly (even a compiler error), to configure the pins incorrectly you destroy the chip.

I always use pullups or pulldowns in SIL resistor packages to minimize the room required. In real tight situations, being as small as they are, I have even soldered them directly to the pin connections on the bottom of the board so they don't require real estate.