spare input pins

[russbow]

In all of my proto / play circuits I have always tied unused inout pins to eth via 10k resistors.

I now want to make a permanent circuit and save footprint / components.

Is it O.K. to tie spare I/P pins directly to ground? I can't figure out a reason why not.

Russ.

 

[eclectic]

In all of my proto / play circuits I have always tied unused inout pins to eth via 10k resistors.

I now want to make a permanent circuit and save footprint / components.

Is it O.K. to tie spare I/P pins directly to ground? I can't figure out a reason why not.

Russ.

A search will bring up several options/opinions , but,
if the pin can be configured as input/output, then use a resistor.

Here's one of several postings:
http://www.picaxeforum.co.uk/showthread.php?t=5697&highlight=input+tie+ground

e

 

[hippy]

The main argument for not doing that is that where an input could become an output high, the short to 0V will likely damage the I/O pin and perhaps the PICAXE. If tied to 0V via a suitable resistor such a situation will not have such catastrophic effects.

The risk of such a situation occuring is for those PICAXE's which have bi-directional I/O where there may be a programming error, and in cases where an external effect may cause corrupt operation of the program or the internal firmware ( EMF, induced noise ).

Connecting to 0V is okay if you are prepared to accept the risk of failure in adverse circumstances. In many cases unused inputs can be left floating ( or not connected and set output low/high ) without having undesirable consequences. The recommemded course would be to tie each unused input to 0V via its own resistor.

 

[Dippy]

.. and using one of those SIL commoned res networks doesn't take much space - though it adds a few pennies.

 

[KMoffett]

Also, using 1/8th watt resistors, mounted vertically saves space.

Ken

 

[SilentScreamer]

Why not tie all unused outputs with one resistor? The risk of two pins, one going high and another going low does still exist but far less likely.

Personally though I'd just leave them floating unless the projects power consumption is very important (in fact, I always do ).

 

[russbow]

Thank you all for your inputs. For the sake of 0.1 inch and tuppence out the coffers, I'll put a SIL in.

R.

 

[BCJKiwi]

And as per a recent thread, those inputs that can be made outputs can be left floating and set as outputs.