Lorick <PICLIST@MITVMA.MIT.EDU> wrote:

> Was I witnessing a coincidence or does this make sense?  When I've
> tried to test-read the contents of a code protected PIC in the
> past, I've gotten all 0's where the code would otherwise be, but
> when I read the code back from my first 2 code protected 16C505's,
> I got the usual message that the device is protected and memory may
> not be valid, but I still saw most if not all of my code get
> dumped...
>
> I compared the dump to the original hex size in the ram window and
> noticed that it seemed to clearly show the code up to around 0x040
> and then it showed still non-zero stuff, but somewhat scrambled.

Lorick:

The old 12-bit PICs (16C5x, 16C505, etc.) use a different copy-
protection scheme than the newer PICs.  When you code-protect a 12-
bit PIC, addresses 0x00-0x3F are NOT protected; you can still read
and write to them.  Addresses 0x40+ ARE protected (more or less);
when you read from them, you get 0x00n, where "n" is the 4-bit sum of
the three nibbles in the memory location.

-Andrew


=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - San Diego, California
=== http://www.geocities.com/SiliconValley/2499

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