> > I've always understood PICs to powerup with their I/O lines set to
> > input; i.e., high impedance.  If you write your code to respect this,
> > to not make the lines outputs and drive them high until after you
> > KNOW the device isn't being reprogrammed, then no worries.
> 
> The code has nothing to do with this, since it won't be running during
> external high voltage programming.

In the case of Vdd-before-Vpp programming, it is possible that some
code could begin executing before application of Vpp puts the chip
into programming mode.

In that case, it becomes the programmer's responsibility to ensure
that if the PIC is powered up to 5V by a programmer, it doesn't do
anything to cause its I/O lines to exceed the acceptable voltage
for devices attached to them.  That could be as simple as using
the powerup timer to delay code execution until the programmer
can assert Vpp, or as complex as the PIC checking its own
voltage and not proceeding with code execution if Vdd > 3.3V
(or whatever).

Mike H.

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