I have been using the PIC 16F and 18F series for several years.  I enable=20
brown-out detection
(BOREN) on all designs.  I have never seen the lock-ups you describe BUT I=
=20
have also never tried
to induce a particularly evil power input transient either.  Power comes on=
=20
in whatever sequence it
likes to but the nominal case is clean in my apps. (24 VDC rail and a=20
switch, linear regulator down to the
PIC device)

Given the criticality of the design you are engaged in I would strongly=20
recommend that you spend some
time to set up and test for "evil power" inputs.  The PIC itself is=20
relatively low power, so some form of
power amp and function generator (8 bit DAC and a table of random numbers a=
s=20
an example, there are
may other stimulii that can be generated from that simple hardware) can be=
=20
used to power the PIC and
simple code within the PIC can be monitored for functionality. If you have=
=20
some sense of what kind of
power inputs are particularly at risk or common in your environment that's=
=20
even better, but by all means
SET UP AND TEST.=20

--=20
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