>
>
>On Sun, Jul 14, 2002 at 06:33:42PM +1200, Jinx wrote:
> > Do I assume correctly that Flash memory on a 16F877 can't
> > be enabled for internal writes and disabled for external reads
> > at the same time ? (Table 4-1 of F877 manual). Is it just that
> > simple or is there a workaround ?


I believe the 16F87xA family resolve this problem as they have
separated code protection and write protection into different
config bits. I have one here and I will be testing this later today
I hope.


>It is just that simple. An unfortunate side effect that one extra bit in the
>config register could have resolved.
>
>BTW from my recent reading of of the 18F series chips, the config register
>is readable and writable programmatically. So it should be possible to to
>only disable code protection under program control. So for example one could
>send an encrypted stream with an authorization code. The internal program can
>temporarily disable code protection, write the new code, then reenable it.
>
>Seems to be workable.


Nope. The 18Fxxx can program its own config area but it cannot remove code
protection as it cannot write a CP bit from '0' to '1'

See DS39564A- section 19.4.1

In any case the 18Fxxx can write to code protected areas if the write protect
bits allow it so you can have a bootloader within a code protected 18Fxxx.


Regards,

Jim Robertson
NEWFOUND ELECTRONICS


>BAJ
>
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