Tony, the FAE for microchip told me that internal flash reads can occur
perfectly well on code protected memory, that the point of the code
protected memory was not to defeat hackers or code copyers, but rather to
protect you from overwriting your own code.  Are you sure that the code
protected flash can't be read with internal flash reading code???

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Tony Nixon
Sent: Wednesday, July 18, 2001 1:16 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: about the flash memory on the 16F877


Ron Anthony wrote:
>
> Hello All.  I am currently struggling with how to deal with the
ridiculously
> bad code protect on the 16F877.  I am hoping to learn a few things from
> those who are actively working with the flash memory.
>
> Here is the primary question:
>
> If I code protect the upper half of the chip, that is, 50% of the flash
> memory, will someone be able to use an ICSP to put in code on the open
lower
> half that can internally read the code protected space and dump the
contents
> out of a port?  Because if they can, there is no sense code protecting
that
> half of the chip.  If I code protect the 256 bytes, can they not read
those
> as well?  From what I understand, internal flash reads work on code
> protected memory.  So it is very easy to set up a memory dump of the code
> protected space.  Is this correct?

You can't read or write code protected ROM from within the chip, or from
a programmer or from ICSP.

Ages ago there was some threads about having a special config bit that
would allow the chip to rewrite itself underneath the code protection.
ie. the ROM can't be accessed from outside the chip but it can be
rewritten internally. That way a bootloader could use encrypted code to
update itself.

Not a reality though and I guess, unless you are confident that the
protected code will not need replacing, then using a bootloader for
upgrades is no option.

--
Best regards

Tony

mICros
http://www.bubblesoftonline.com
mailto:sales@bubblesoftonline.com

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

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