Peter van Hoof wrote:

> put some diodes between outputs and keys to prevent blowing up outputs
> if more than one key at a time is pressed (my kids would be great in
> testing this)  The other possibility is to only switch one of them to
> output and keep the others inputs.

  No, actually you switch them between input and output low controlling
the TRIS A register while all PORTA bits are written as zero.  You also
use inbuilt port B pull-ups (not pull-downs as was alternatively
mentioned).

  That's what they are there for.  Similarly, while it sleeps, you can
pull *all* the port A strobes low and use port B interrupt-on-change to
wake it.  Even whilst "awake" and not using port B interrupt-on-change,
this is the simplest way to poll for any keypress.
--
  Cheers,
        Paul B.