Bit security pic

Hi, you know if the pic 16c621 16c622a windows, once programmed and
protected they can be cancelled? because I am having problems...
Thanks...

kerek@libero.it (roberto) writes:
> Hi, you know if the pic 16c621 16c622a windows, once programmed and
> protected they can be cancelled? because I am having problems...

They cannot.  Microchip deliberately buried the security bit under
metalization to make it more difficult for someone to deencapsulate
a plastic OTP part and erease the security bit, thus enabling the
program memory to be read out.

This has the unfortunate consequence that the security bit of the
windowed EPROM parts cannot be erased either, since they use the
same die.