David Nicholls wrote:
>
>         Wow !
>                 Would anyone else like to confirm this mail. (That even
> new pics can have CP bit erased given enough UV light ). Not that I'm
> doubting you Mike just curious if Microchip would like to confirm that
> this is a design feature rather than a fault in Mike's chips...

Not that I've played with a lot of windowed chips but......

Wouldn't the design of the devices be such that the CP bit
was under another metallisation layer? This would make it fairly
(but possibly not completely) opaque to UV. I certainly wouldn't
be suprised if it could be erased given enough UV.

Of course the CP bit could be implemented as a true fuse.

What's the security problem with just ensuring that the CP bit takes
*much* longer than the code to erase anyway? It's not as if anybody
with the resources to defeat the CP bit (eg by selectively exposing
it) wouldn't be likely to have the resources to defeat it no matter
how it was implemented........




Stuart.