> > The important thing is to avoid having a tri-stated (input) pin
> > floating,
>
>   This is ludicrous!  So it might add a few dozen microamps to the
> current draw.  Not half as much as if your suggested pull-up resistor
> is accidentally pulled down by the same circumstance.

I don't think the current flow is the main problem here. A floating
input WILL cause erratic chip operation. Maybe not while you force it
to, but at some stage it will. I've had chips do all sorts of wierd
things, until I eliminated a floating pin (or pins). Some of these chips
froze just by placing a finger near them, some won't start, some start
but run 'funny'. The worst problem is spending mutitudes of time finding
out 'why', when you haven't realised the floating pin is the culprit. As
far as I know, the excess currents are caused by input FETS not knowing
what to do and the 'hi' and 'lo' ones turning on at the same time
causing minute rail to rail shorts, which could be at any frequency.
Surely this causes wonderful things to happen inside the die, false
triggering the brown out detect etc. - who knows?.

My opinion, is that there is some credibillity in using a moderate value
resistor to 'babysit' unused pins. Besides, there is your pin pad for
other uses if need be :-)


--
Best regards

Tony

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