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'Aghhh Code Protection Bit Problem .... (fwd)'
1997\02\12@113839 by David Nicholls

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part 0 26415 bytes content-type:TEXT/PLAIN; CHARSET=US-ASCII

hi there,

       Yesterday my worst nightmare occured, I think I may have
inadvertently programmed the code protection bit on my PIC16C74JW. I'm not
sure exactly how this happened. I have been using a home made programmer
very succesfully up until now, but this time something strange happened
the pic blankchecked ok programmed ok and then failed the verify.. At
first I wasn't too worried but then I read back the code with a different
package and this told me that the code protect bit had been set.
Needless to say I was pretty disturbed that my 40 IRpounds chip
had been effectively ruined.
       What I would like to find out from the list is
1. Is there anyway of undoing the code protect ?? (I assume not !)
2. If I cant undo the code protect is there any way I can reprogram the
  chip, even if I can't verify the code I write ?
3. If I buy a new chip what are the chances of me doing this again.
4. Am I correct in assuming that it only takes a one bit error when
reprogramming the PIC to actually wreck your PIC.
5. Where are the fuses stored in memory are they part of the hex code you
read back or is there a special bus instruction to access the fuses area
of the pics. Is there any way I can be sure If I get another PIC that I
don't do this again. Even if there is a hardware error in my programming.
What I mean is for example
If the download method is as follows
1. Send start signal
2. Download bit stream of CODE to PIC
3. Follow directly with bit stream of FUSES 010010.. etc
4. END
If the above assumption is correct then I would be worried that a single
bit error in the fuses stream could destroy my second PIC.
However if on the other hand it follows the pattern of
1. Send Start Signal
2. Download bit stream of CODE to PIC
3. Send "Prepare to recieve FUSES code" (If fuses are to be set)
4. Now send Fuses bit stream.
5. END
With the latter arrangement It could be possible to only program the code
area and never send the "Prepare to recieve FUSES". This way I could be
quite sure not to accidently set a CP FUSE. Assuming my spurious error
doesn't send the correct byte to prepare for fuses.. (Fairly safe.)
However I just realised I probably need to set my crystal fuse.. Aghhh is
there any way to be safe.. One bit really isn't a big error for the price
of the chip..
       Anyway sorry for such a long posting. Any help or comments
appreciated..

                               Thanks.
                                       David.

P.S. I've included my original hex and readback code in case anyone can
magically look at such cryptic figures and go " Ahh I know what happend"
(Not likely I'd say) Everyone else delete at will !.



Http://http://www.csn.ul.ie/~david


Content-Type: TEXT/PLAIN; CHARSET=US-ASCII; NAME="RS232.HEX"
Content-ID: <spam_OUTPine.LNX.3.95.970212162652.20083BTakeThisOuTspamskynet.csn.ul.ie>> Content-Description: original hex

:020000000528D1

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Content-Type: TEXT/PLAIN; CHARSET=US-ASCII; NAME="READBACK.HEX"
Content-ID: <
.....Pine.LNX.3.95.970212162652.20083CKILLspamspam@spam@skynet.csn.ul.ie>> Content-Description: read back code.

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:00000001FF

1997\02\12@124416 by Bob Fehrenbach

picon face
David Nicholls <davidspamKILLspamSKYNET.CSN.UL.IE> wrote:
>        Yesterday my worst nightmare occured, I think I may have
>inadvertently programmed the code protection bit on my PIC16C74JW.

David,

  Not that it is any consolation but I am looking at 3 PIC16C62A/JWs
  out of a group of 5 that I had been using.  These 3 all mysteriously
  got code protected.  Even though I have been especially careful and
  am using a Microchip Promate programmer, it still happened.



--
Bob Fehrenbach    Wauwatosa, WI     .....bfehrenbKILLspamspam.....execpc.com

1997\02\12@125936 by Mike

flavicon
face
>David,
>
>   Not that it is any consolation but I am looking at 3 PIC16C62A/JWs
>   out of a group of 5 that I had been using.  These 3 all mysteriously
>   got code protected.  Even though I have been especially careful and
>   am using a Microchip Promate programmer, it still happened.

I understand that on HC705 series any code protection is via EPROM bit,
I infer that code protection on PIC is via a fuse and therefore cannot
be erased by UV ?

Does this also apply to the flash parts - wouldn't it be more efficient
that the code protection be via EPROM type bit anyway ?

Are there any moves by microchip (hi guys) to change to EPROM bit ?

And in any case since I hear that all code protected PIC parts are just
as easy to read as the code protected motorola parts - wouldn't it be
logical that a code protect chip could be erased and reused ?

Rgds


Mike

1997\02\12@134229 by David Nicholls

flavicon
face
On Thu, 13 Feb 1997, Mike wrote:

> >David,
> >
> >   Not that it is any consolation but I am looking at 3 PIC16C62A/JWs
> >   out of a group of 5 that I had been using.  These 3 all mysteriously
> >   got code protected.  Even though I have been especially careful and
> >   am using a Microchip Promate programmer, it still happened.
>
> I understand that on HC705 series any code protection is via EPROM bit,
> I infer that code protection on PIC is via a fuse and therefore cannot
> be erased by UV ?

Yeah I'd imagine so !

>
> Does this also apply to the flash parts - wouldn't it be more efficient
> that the code protection be via EPROM type bit anyway ?
>
> Are there any moves by microchip (hi guys) to change to EPROM bit ?
>
       I hate to say it but  I recon judging by previous discussions I
have heard that the move was actually in the other direction. I reckon
that it may have been due to a worry by microchip that one may be able to
selectively erase parts of the windowed chip using perhaps a fine laser
beam or something. And by doing so only wipe the CP bit.. I.e. exposing
the protected code..
       I am no expert on the subject so all I have just said is purely
hearsay. Please correct me if I'm wrong in those assumptions.
       However on the note of Microchip doing something about the problem
I would suggest and hope I'm taken seriously that a variant of the
windowed chip be produced that has no code protect bit.. Surely this
wouldn't be difficult (I realise Chip changes incur fabrication costs )
but I believe there would definately be a large market for such chips as
most developers have no need to code protect their windowed versions..
It's easier to lock them in your drawer ! Could anyone who agrees with
this suggestion please voice your support to confrim such a market.





> And in any case since I hear that all code protected PIC parts are just
> as easy to read as the code protected motorola parts - wouldn't it be
> logical that a code protect chip could be erased and reused ?
>

       Hmmmm, Are you sure on that one ? I'm sure microchip wouldn't be
impressed !

> Rgds
>
>
> Mike
>


                                       Dave.



http://www.csn.ul.ie/~david

1997\02\12@140138 by Norm Cramer
flavicon
face
Seems like they could have added a bit "code protect disable".  When this
fuze gets blown, you can nolonger code protect.  This would allow us to
make the chip "un-protectable" for development and still be able to protect
them for production.  If the code protect is enabled before code protect
disable, then the chip would forever be code protected.  If the code
protect disable was "enabled" before the code protect, the chip would be
un-protected forever.  Both bits should be un eraseable.

Any thoughts.

Norm

At 06:34 PM 2/12/97 +0000, you wrote:
{Quote hidden}

1997\02\12@141609 by Tim Kerby

picon face
Hey, is it a 74 or 74A?
I think the 74 can be uv erased.  If you have been using the 74 and this
chip is a 74a then some config bits are inverted possibly including code
protect.


Tim


------------------------------------------------------------------
If you can read this, it is the end of the message!
My web pages are at http://web.ukonline.co.uk/members/tim.kerby/
My PIC site is at web.ukonline.co.uk/members/tim.kerby/pic/
It needs your projects!
------------------------------------------------------------------

1997\02\12@141614 by Tim Kerby

picon face
I agree
We are planning to introduce the PIC to the Scottish Education system as my
teacher now has a job involving this.  We sure could do with this as
pupils, code protect and chip prices don't go well together.


Tim

At 12:58 12/02/97 -0600, you wrote:
{Quote hidden}

------------------------------------------------------------------
If you can read this, it is the end of the message!
My web pages are at http://web.ukonline.co.uk/members/tim.kerby/
My PIC site is at web.ukonline.co.uk/members/tim.kerby/pic/
It needs your projects!
------------------------------------------------------------------

1997\02\12@143850 by David Nicholls

flavicon
face
On Wed, 12 Feb 1997, Tim Kerby wrote:

> Hey, is it a 74 or 74A?
> I think the 74 can be uv erased.  If you have been using the 74 and this
> chip is a 74a then some config bits are inverted possibly including code
> protect.
>
>
> Tim

       Actually I'm using the 16C74. And I haven't tried UV erasing it
yet. Actually I was afraid to erase it in case someone came back and said
... " Well you can actually undo the code protect bit as long as you don't
attempt to UV erase it first ! ". Not likely to happen at this stage.
       I don't have access to an eraser until tommorow so I'll let you
know if it works. I had been under the impression though that the policy
was that all new PICs would have fuse CP's thus only the older 74's in
stock would be UV erasable.
       Also can someone confirm what Tim mentioned about the CP bits
being inverted on 74A. My programmer software is supposed to support 74A.
I'm not sure yet how it knows what chip it is ?? Although I had programmed
before using same software...

                               Dave.


http://www.csn.ul.ie/~david




>
>
> ------------------------------------------------------------------
> If you can read this, it is the end of the message!
> My web pages are at http://web.ukonline.co.uk/members/tim.kerby/
> My PIC site is at web.ukonline.co.uk/members/tim.kerby/pic/
> It needs your projects!
> ------------------------------------------------------------------
>

1997\02\12@143854 by David Nicholls

flavicon
face
Absolutely..
       This sounds like the best idea yet !!


On Wed, 12 Feb 1997, Norm Cramer wrote:

{Quote hidden}

1997\02\12@233300 by John Payson

picon face
> On Wed, 12 Feb 1997, Norm Cramer wrote:
> > Seems like they could have added a bit "code protect disable".  When this
> > fuze gets blown, you can nolonger code protect.  This would allow us to
> > make the chip "un-protectable" for development and still be able to protect
> > them for production.  If the code protect is enabled before code protect
> > disable, then the chip would forever be code protected.  If the code
> > protect disable was "enabled" before the code protect, the chip would be
> > un-protected forever.  Both bits should be un eraseable.
> >
> > Any thoughts.

> Absolutely..
>         This sounds like the best idea yet !!

I prefer a slightly different variant: the device incorporates a code-protect
bit and a code-protect-write-enable bit.  When an OTP is shipped from the
factory, the latter bit is set; for a UV device it is not set.  While it would
be possible for a programmer to--with enough trouble--burn the protect-enable
pin and then burn the protect bits themselves, this would not happen without
deliberate action.

As a simpler alternative, Microchip could simply document the behavior of one
of their "test" locations sufficiently to say that it will be blank on all
UV devices and non-blank on OTP's.  A programmer could then simply decline to
code-protect any device whose test area was blank.  This alternative may be
the best because it could be accomplished with no change to the die whatso-
ever; only a slight change in handling (to erase the window parts before ship-
ping them) and in the documentation.

On a related note: is there any reliable (blessed by Microchip) method of
identifying a part to be programmed?  Programming a 16C622 as though it's
a 16C84 seems to damage the poor thing rather severely...

1997\02\12@233525 by John Payson

picon face
> Hey, is it a 74 or 74A?
> I think the 74 can be uv erased.  If you have been using the 74 and this
> chip is a 74a then some config bits are inverted possibly including code
> protect.

If memory serves, the problem is not that bits are inverted, but rather that
Microchip wrote that "reserved" bits should be written as zero.  As a
consequence of this, any programmer which expects the old device and honors
the "reserved" designation will write zeros in all the additional code-prot-
ect fuses on the 16Cxx.  Boing!

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