> In designing circuits with CMOS chips, the basic rule is that you should
not
> leave any unused inputs floating. They are tied either to +V or Ground or
> there is a pull-up / pull-down resistor. Is the same rule applicable when
> you design circuits using PIC micros? If you define a port or a pin as
> input, are there internal pull-up / pull-down resistors that are enabled
> automatically?
>

The rule is indeed applicable to PIC processors with I/O configured as
inputs.  The same sorts of high currents flow when a PIC's inputs start
wavering near the bias points of the input transistors.  There are no
internal pull-ups or pull-downs that enable automatically.

There *are* however, internal pull-ups on PortB in most PICs.  You can use
these to pull up any pins configured as inputs and left floating.

Personally, if I don't use a pin in a design, I will configure it as an
output in software.

-d

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