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PICList Thread
'Un-erasable memory in a 16C74A'
1998\03\10@023359 by Caisson

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Hello Pic-Listers,

 Just now something strange happened to me, or rather to both 16C74A Pic's
I've got here.  Before today they worked fine.  Programmed & erased them
some
times (about 2-3 times a day for 3 months, nothing special I think).  But
suddenly
my programmer (PicStart+) told me that my Pic's where not empty.  O.k I
tought,
lets erase them some more (50 minutes totally).  Nothing changed, they
still
where not totally erased.  O.k. , lets read and check them.  To my surprise
the
first 0400 hex bytes where fine, the rest (from 0400 up) were Zero's.

eehhmmm...  That could be the Code-protect !  Let's check it ... No, its
still Off,
even after read-out of the Pic's memory.   Now I'm baffeled,  No
Code-protect,
Nothing strange in my program, but _BOTH_ my pic's showing this strange
behavour.

Anyone there who knows what happened here ?

Greetz,
  Rudy Wieser

P.s.
My question allready found his way to MicroChip (Holland) and they asked me
toe send them the Pic's, cause the didn't know what could be wrong either
..

1998\03\10@042016 by Orin Eman

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>   Just now something strange happened to me, or rather to both 16C74A Pic's
> I've got here.  Before today they worked fine.  Programmed & erased them
> some
> times (about 2-3 times a day for 3 months, nothing special I think).  But
> suddenly
> my programmer (PicStart+) told me that my Pic's where not empty.  O.k I
> tought,

Wonder if it's the PicStart+.  Mine mostly refuses to work with
16C73s.  Sometimes claims they are programmed when they are blank.
Reads _note this_ all zeros sometimes, all ones other times.

ITU Tech PIC-1+ is perfectly happy with the same PIC and programs
it just fine.

Orin.

1998\03\10@070440 by Williamson

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[Charset ISO-8859-1 unsupported, filtering to ASCII...]
> Hello Pic-Listers,
>
>   Just now something strange happened to me, or rather to both 16C74A Pic's
> I've got here.  Before today they worked fine.  Programmed & erased them
> some
> times (about 2-3 times a day for 3 months, nothing special I think).  But

I read somewhere (but I cannot remember where) that the UV erasable 74A's
were only guaranteed to work for around 100 erasures.  I may be mis-
remembering, but if I am not, that may be the problem as you are definitely
approaching that limit.

Jason

PS  In the same place, I remember reading that the electrically programmed
84's could be programmed like 10000 times.  Neat-o.

1998\03\10@130204 by schupet

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Hi,
It happened to me also and it caused by ESD.
Peter

Caisson wrote:

{Quote hidden}

1998\03\11@025452 by Caisson

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> Van: Orin Eman <spam_OUTorinTakeThisOuTspamWOLFENET.COM>
> Aan: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Onderwerp: Re: Un-erasable memory in a 16C74A
> Datum: dinsdag 10 maart 1998 10:18

[Cut]

> Wonder if it's the PicStart+.

Don't wonder anymore, it is !

Greetz,
 Rudy Wieser

1998\03\11@201143 by schupet

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Hi

It is definetely not the PicStart+.
It caused by ESD damage.
Altough so many people in the PicList does not believe
ESD can cause that type of damage.

Peter

Caisson wrote:

{Quote hidden}

1998\03\11@204040 by schupet

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Hi,
Exactly as You stated, one of address line blown by ESD.
The strange thing is all the time the same lines blown, probably the
most sensitive and weaker as ESD goes.
I have 4 device with absolutely the same problem and same addresses not
deletable. So it can not be the circuit because it quaranteed I have
different one.

Peter

jimford wrote:

{Quote hidden}

Pic's
> > > I've got here.  Before today they worked fine.  Programmed & erased them
> > > some
> > > times (about 2-3 times a day for 3 months, nothing special I think).  But
> > > suddenly
> > > my programmer (PicStart+) told me that my Pic's where not empty.  O.k I
> > > tought,
> > > lets erase them some more (50 minutes totally).  Nothing changed, they
> > > still
> > > where not totally erased.  O.k. , lets read and check them.  To my
surprise
{Quote hidden}

me
> > > toe send them the Pic's, cause the didn't know what could be wrong either
> > > ..
>
> Sounds like one/more of the address lines on your devices has got blown.
> Could be something wrong with the target u are plugging them into, hence
> 2 failed in same way.    The fact that the EPROM data is bad from a
> round address (like 0400h) suggests an address problem to me.
>
> jim ford

1998\03\12@062724 by Andy Kunz

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>eehhmmm...  That could be the Code-protect !  Let's check it ... No, its
>still Off,
>even after read-out of the Pic's memory.   Now I'm baffeled,  No
>Code-protect,
>Nothing strange in my program, but _BOTH_ my pic's showing this strange
>behavour.

I have the same problem with a couple '73A's.  Perhaps the MCHP lurkers on
this list would like to present this to the factory?

I just bought 850 PIC16C73/JW chips, and it would really not be too popular
to find out that they are overly sensitive to ESD or something.  I plan on
buying 5,000-15,000 '77/JW chips late summer, and you can be sure we're
going to have to investigate this one before THAT order is given.

Andy

==================================================================
                    Andy Kunz - Montana Design
         Go fast, turn right, and keep the wet side down!
==================================================================

1998\03\12@063558 by Caisson

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> Van: Peter Schultz <EraseMEschupetspam_OUTspamTakeThisOuTdvp.com>
> Aan: PICLISTspamspam_OUTMITVMA.MIT.EDU
> Onderwerp: Re: Un-erasable memory in a 16C74A
> Datum: donderdag 12 maart 1998 0:36
>
> Hi
>
> It is definetely not the PicStart+.
> It caused by ESD damage.

It crossed my mind too, but ESD could not explain the fact that _TWO_ Pic's
developed an equal problem at the (for me) same moment.

Oh, before I forget to mention it, I've programmed 16C77 Pic's with the
same
PicStart+ and all things went O.K.  No problems.

So, I can cancel-out ESD damage to my Pic's and PicStart+ (unless its
intermittent ofcourse).

> Altough so many people in the PicList does not believe
> ESD can cause that type of damage.

Once fried a C64 disk-drive controller because of it, just when I remedied
the
problem it had.  Was not funny.  But a great example of ESD and
unforgettable.

> Peter
>
Greetz,
 Rudy Wieser

1998\03\12@063600 by Caisson

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> Van: Peter Schultz <@spam@schupetKILLspamspamdvp.com>
> Aan: KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
> Onderwerp: Re: Un-erasable memory in a 16C74A
> Datum: donderdag 12 maart 1998 2:33
>
> Hi,
> Exactly as You stated, one of address line blown by ESD.

Sorry to but in, but it couldn't be _a_ addressline, becouse of the fact
that to
get the effect i've mentioned you would need _two_ address-lines destroyed.
And, if you destroy an address-line you would (normally) see copies of your
first code-block, not Zero's.

But, to agree with you, it (the  ESD) could have affected the Code-protect
hardware, in such a manner that the code-protect was enabled _without_
regards to the fuses that normally steer that function.

> The strange thing is all the time the same lines blown, probably the
> most sensitive and weaker as ESD goes.
> I have 4 device with absolutely the same problem and same addresses not
> deletable. So it can not be the circuit because it quaranteed I have
> different one.
>
> Peter
>
[Cut]
Greetz,
  Rudy Wieser

1998\03\12@115125 by schupet

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Hi,

For me a similarly defective devices still a beliveble ESD.
Just think about lightning it will goes wherever the shortest and
easiest discharge path goes. My opinion is same with ESD.
If  the devices has one pin which can damaged by 1000V (because
of the chip layout) and rest of them only will damaged by 5000V
my understanding is all the time the 1000V pin will destroyed.
Altough I never did any tests in that matter, chips are to expensive
for that kind of game. Easier to follow some safety precaution.
Since I follow some basic rules I do not have any bad device.

Peter

Caisson wrote:

{Quote hidden}

1998\03\12@150139 by schupet

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Morgan Olsson wrote:

{Quote hidden}

That is true and those devices damaged exactly because of lack of
properhandeling.
( Kind of difficult to short Vcc and Vdd every time when you
program the chip and run to the unit to place in and make sure it is working
especially if your boss is behind you and kindly remind you this project was
due two weeks ago.)
/Peter

>
>
> So, an unconnected device can get damaged randomly (because of process
> variation) anywhere when handled unproperly.
> /Morgan

I desaggree on that one, if process would be so different we could not design
anythingunless measure every pieces and make sure what their parameters are.
The latest silicon processig technology is so good they manufacturing millions
of
pieces with a very low fallout and if you measured them they are pretty well the
same.
But I was talking about the layout inside of the chip, on the silicon. As you
know
they have  wires,
jumpers, gates .... processed from silicon. My understanding is, this layout has
weeknesses
as a usual layout has. If they have to wire to close or sharp corners... the ESD
going to
strike there, because looking for the easiest path to discharge.
I had MOS-Fet transistor ESD damage picture taken with electron microscope
and clearly shows ESD was strike where the gate insulation was the weakest.

/Peter

{Quote hidden}

1998\03\13@065050 by Caisson

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> Van: Peter Schultz <EraseMEschupetspamdvp.com>
> Aan: RemoveMEPICLISTEraseMEspamEraseMEMITVMA.MIT.EDU
> Onderwerp: Re: Un-erasable memory in a 16C74A
> Datum: donderdag 12 maart 1998 17:47
>
> Hi,
>
> For me a similarly defective devices still a beliveble ESD.

Yes, Two devices, twice a ESD discharge, two problems.

But think of it: Two devices, programmed about 5 to 15 minutes after each
other, developping the _same_ problem.  ESD could zap one of them, but
to zap _both_ of them at allmost (but not totally) the same time after 3
months of usage is to much for me.

> Just think about lightning it will goes wherever the shortest and
> easiest discharge path goes. My opinion is same with ESD.
> If  the devices has one pin which can damaged by 1000V (because
> of the chip layout) and rest of them only will damaged by 5000V
> my understanding is all the time the 1000V pin will destroyed.

You could be right _IF_ the ESD was introduced at the same pin(s)
every time.  If the ESD is provided on random pins (and the thingy has
40 of them) the results should change dramatically.  if they don't, we
could have found a 'weak spot' ...

> Altough I never did any tests in that matter, chips are to expensive
> for that kind of game. Easier to follow some safety precaution.
> Since I follow some basic rules I do not have any bad device.

Auch! that's a slap on the wrist :-)  But your'e right again. I could not
hurt to try to stay ahead of problems.

> Peter
>
Greetz,
 Rudy Wieser

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