re: Code Protect Bit

   Byron (and others in this discussion), why is this an issue? Setting the
code protect bit is kind of like pulling a pin on a hand grenade and letting
go of the handle. Once you've done it, you're committed... I can't see any
R&D-related purpose in setting the bit. Asking Microchip to allow erasure of
the bit, or an alternative bit, in the "JW" parts, seems a bit ridiculous to
me considering the chip process issues. Byron, this is not directed to you
but the discussion in general.

   - Tom

At 12:50 PM 4/26/97 -0400, you wrote:
>>
>> At 09:23 AM 4/26/97 -0400, you wrote:
>> >>
>> >> Hi all!
>> >> Thanks  all for help.
>> >> To me was managed to erase the bit of protection UV eraser
>> >> during 3 hours and to record the new program.
>> >
>> >So it seems to me that this is the best way to do it. The code protect
>> >bit can be erased, but there is absolutely no way any part of the program
>> >will still be there (after 3 hours) once it is erased.
>> >
>> >This is good to know.
>> >
>> >
>> >
>> >BAJ
>> >
>> Maybe I'm old and I missed it but I have been lurking for the last few days
>> and I don't believe I saw anyone drop the magical reference "A" to the
>> discussion on the 16C74 protection bits.
>
>I was presuming that this discussion was about the supposedly "non-erasable"
>parts: i.e. 'A' suffix parts and new parts with no 'A' suffix equivalents.
>
>>
>> It goes like this, the 16C74 (without the "A" suffix) can be erased and
>> reused after code protection BUT eraseure time for a protected device can
>> be 2 to 3 hours! Normally it is 10-20 minutes ball park without protection.
>>
>> If the part is a 16C74"A" then it is "sudden death." If you write a "0" to
>> anyone of the multiple code protect bits then protection is enable and is
>> not UV erasable. Rather an expensive OTP!
>
>I thought this part was the point of contention. From what I was reading
>that shining high intensity UV light for extended periods of time would
>eventually provide enough UV through the metallization over the fuse to
>erase it. It would take a long long time, but the part could be erased.
>
>Since this has now been pointed out can we get a clarification?
>
>Bottom line: a totally unerasable code protect bit is quite useless for
>JW parts. The OTP parts already have the plastic cover as the first line
>of defense against code protect erasure. It seems that the supposed
>semi-opaque metallization layer is a good idea. Totallay opaque though,
>just doesn't make any sense.
>
>BAJ
>
>