> Has any one ever experienced an 18F452 or 18F252 going into self destruct
> mode.   If I switch the power off and on real fast occasionally the chip
> will Start to overheat and eventually burn up.   This should not happen.
> But it does.  Nothing is connected to the chip other than 10K hold up
> resistor, 10Mhz Resonator and +5v power.

Do you really mean NOTHING else?
Is only one I/O pin terminated.
Are unterminated IO pins set as outputs?
Are all input IO's terminated.
Failure to define IO pins can allow them to be pulled to undesired levels by
transients.

It is  possible that turning power off then on leaves one or more pins at a
high level after Vdd drops. Turning Vdd on may trigger a latch up condition
if an input is too high. Are there capacitors on some IO pins or something
that could hold them high after Vdd falls?

As someone said, it SOUNDS like latchup. This occurs when a parasitic SCR
formed with the gate transistors and the substrate layer is biased on. Once
on it stays latched on until power is removed. Taking pins outside their
design limit voltages is a good way to cause this. Hence the above
questions.



        Russell McMahon

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.