> Most of the mid range PICS that I have used, including the 16F628, have a
> programmable pull up on port B, enabled by bit 7 of the option register.
> It is an enormous convenience and a saver of real estate not to have to p=
ut a
> pull up on every switch input.

The major problem with using internal pull-ups is they are quite high imped=
ance, and if used on a floating pin can be subject to hum pickup injection =
because of the impedance. This may not be a problem when used with switches=
 that have a 10n or so capacitor for debounce, but with no connection at al=
l on the input is asking for trouble.

The best score is to set any unused pin to an output, and the recommendatio=
n from Microchip is to set the output low for minimum current draw. I assum=
e this is a function of the internal circuitry required to drive the high s=
ide transistor if set to a '1' state, but that is the recommendation for an=
y system wishing to penny pinch the last micro amp of current drain.

--=20
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