Is should be possible to use an XTAL and free the OSCAL value for
programming
of a special code.  If someone simply copies your program, and reproduces
it,
the OSCAL value will not match.

If you do some sluethy offset, math and pointer stuff, you could read it
without
'pointing' at the OSCAL, and put the unit to sleep.  Better yet, have it
work
fine, except that it corrupts itself, and resets from time to time if the
correct
value isn't there.  The pic CLUB, if you will.

Another idea is to do a bunch of current measurements at production, and
store
them in eeprom.  Then if the detected current at specific stages is
in-correct,
due to probe load, disconnected I/O, etc., the unit could become evil and
inflict
it's wrath!

The theif will have to work for it then, and maybe we can enrich their skill
by
bringing them out of the depths of theivery and into engineering. MTWABP LA
LA LA

Craig


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Graeme Smith
> Sent: May 2, 1999 11:03 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Self destruct schemes that thwart reverse engineering - Way
> [OT]
>
>
> Hmmm....
>
> How about setting up a "Chip Protecter" linked to a pic pin that is only
> used to "Read" the chip. this "Chip Protecter" blows when they try to read
> the chip, thus turning off the oscillator, and shutting down the pic.
>
> They can read the chip, but they can't use the same circuit to test it....
>
> (Unless they replace the chip protecter).
>
> another possible approach, is to set up a circuit so that no matter how
> the chip is reprogrammed, unless it gets a certain voltage on one of the
> pins, it will automagically shut down... can be set up so that it checks
> the chip-id to make sure it is on the same chip, or to a timer so that it
> will run for about 20 minutes, and then shut down permanently. (blow a
> chip protect fuse?)
>
> Of course mis-using this to do planned obsolescence is considered bad
> design... isn't it?
>
>                                 Grey
>
> GRAEME SMITH                         email:
> grysmith@freenet.edmonton.ab.ca
> YMCA Edmonton
>
> Address has changed with little warning!
> (I moved across the hall! :) )
>
> Email will remain constant... at least for now.
>