>
> 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