Re: leaving pin floating

In article <pan.2006.12.27.18.45.50.724758@xxxxxxxxxxx>,
rich@xxxxxxxxxxx says...
On Wed, 27 Dec 2006 09:35:33 -0800, Arlet wrote:
James Beck wrote:
luhanis@xxxxxxxxx says...
Luhan wrote:
A. Lemon wrote:

Is it so bad to leave an input pin floating (from a PIC)?

Is the increased current consumption from input noise at threshold
point the only drawback?

What is you reason for floating the pin???

Floating pins can cause a lot of noise spikes and you just never
know which one will cause a problem some time.

On second thought, I leave pins 'floating' all the time while
prototyping PIC designs! I just program them all as outputs if they
are not otherwise used.

As it had been pointed out, there is a finite time that the pin is in
its' default condition (and in PICs it is usually a high impedance
input) before you make it an output and drive it to some state. Never a
good idea. Resistors are cheap.

If you insist on doing that, you should also put resistors on all output
pins that have a high impedance load.

Why?

Thanks,
Rich
Yeah, why?
If the pin was an input to start with and then gets set to an output I
can see making sure there is something there other than the cap on the
gate of a FET, but if the output is a dedicated out then there are
probably low impedance drivers holding a state.
Maybe I'm missing something. Wouldn't be the first time.

Jim
.

Relevant Pages

  • Re: leaving pin floating
    ... Luhan wrote: ... Is it so bad to leave an input pin floating? ... Is the increased current consumption from input noise at threshold point the ...
    (sci.electronics.design)
  • Re: leaving pin floating
    ... Is it so bad to leave an input pin floating? ... Is the increased current consumption from input noise at threshold point the ...
    (sci.electronics.design)
  • Re: Leistungsaufnahme Festplatte
    ... formationen gefunden. ... eben umbauen. ... Floating sollte reichen und deshalb koennte ein simpler ... weder lasse ich die Sache wie sie ist oder ich zwicke den Pin 11 weg. ...
    (de.comp.hardware.laufwerke.festplatten)
  • Re: leaving pin floating
    ... But what does ESD have to do with a pin having a pullup, or leaving ... I don't see what benefit it has at all for ESD, ... you just had a tiny exposed pin. ... So you think having a highZ input just floating there is better than ...
    (sci.electronics.design)
  • Re: leaving pin floating
    ... Is it so bad to leave an input pin floating? ... Is the increased current consumption from input noise at threshold point the ... Resistors are far too much trouble for prototyping. ...
    (sci.electronics.design)