At 03:08 PM 8/13/97 -0400, Martin R. Green wrote:
>You might not have fried them after all.  I have heard that one of the ways
>MicroChip increased the security of their devices is to increase the UV
>exposure needed to erase the configuration bits.  This is because some
>enterprising souls figured out how to manipulate the chip voltage and
>erasure techniques to clear the code protect bit while still leaving the
>code itself intact.  By making the configuration bits much harder to erase,
>the contents of the program memory will be gone by the time the protect bit
>is cleared.
>
>Anyway, it could be that you just need to increase your erase time over
>what you had been using, since your programmer might report that device is
>not blank even if only the configuration byte is non-blank.
>
>If you are using old (pre-used) chips that you KNOW don't have the new
>security features, your chips might still be OK.  UV light sources weaken
>with age, and it is possible that all you need to do is increase the erase
>duration to compensate.  If you find it take a lot longer to erase chips
>now, you might want to replace your UV tube.
>
>Finally, check for dirty quartz windows on the chips themselves, and maybe
>(this one is a stretch) the chips are just getting harder to erase with
>age.
>
>
>CIAO - Martin R. Green
>elimar@bigfoot.com

I've got 8 chips exhibiting this behaviour, and I tried erasing for 20 min.
without success.  I'm using relatively old chips, I believe, but even with
the code protection, would 20 min. be reasonable?

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