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'Code Protect Bit (info)'
1995\06\30@143115 by stle.cudenver.edu>

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> Date: Fri, 30 Jun 1995 07:42:58 -0600
> From: Harrison Cooper <spam_OUThcooperTakeThisOuTspamDS9.SIM.ES.COM>
> Subject: Code Protect Bit (info)
>
> While at the seminar, they were talking about code protection.  They said
> that on the windowed parts, the masked to code protect location such that
> if you set the code protect bit and burned it, it would not erase this
> location, thus rendering the part useless.

I think this is something on newer parts; I have two 17C44 engineering
samples that are now doorstops, or paperweights (depending whether they're
resting legs-up or legs-down, I guess).

I have programmed and erased 17C42/JW parts dozens or hundreds of times, and
it made me very comfortable to know that the last, exact .HEX file I tried
in the windowed part was exactly the same, embedded fuses and all down to
the exact checksum, as the .HEX file handed over to manufacturing.

The 17C44 has an added ``feature'' that the definition of code protection
includes a fuse area that is unerasable.  And since OTP and windowed parts
are built from a common die pool, the mechanism intended to prevent prying
open and selectively erasing plastic DIP parts also prohibits use of code
protect on windowed parts.  Yes, you can erase everything ``else'', but then
you have an erased, windowed part that refuses programming.  It can't tell,
and doesn't care, that the code it is protecting is blank.

Peter F. Klammer, Racom Systems Inc.                   .....PKlammerKILLspamspam@spam@ACM.Org
6080 Greenwood Plaza Boulevard                            (303)773-7411
Englewood, CO  80111                                  FAX:(303)771-4708

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