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'[PIC]: EEPROM Corruption'
2002\08\01@053721 by sbryden

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I just had a weird case of EEPROM corruption on a 16F84. The first 14 words
were overwritten to the value 0xAE during a thunderstorm which tripped the
power.

The thunderstorm is probably a red herring, and the power loss may be more
likely to be a contender, but I have cut the power using the same breaker
before without incident.

My thinking is this - either the EEPROM just "corrupted itself" which seems
unlikely, despite possible brownout, since there was definitely no write
happening, and the fact that the corrupt data was 14 times 0xAE.

Second possibility - I have a routine in the code which copies a block of RAM
to EEPROM. It takes the RAM address in FSR, EEPROM address in EEADR and length
in w. If my program counter went awol and hit this code with random values,
anything could have happened, although that would suggest that there was a
block of ram with the same 0xAE bytes, which also seems unlikely.

I have since decided to modify the routine so that the calling code sets WREN
or something to minimise the effect of this code being run when it shouldn't.

Does anyone have any thoughts on what could have caused this? BTW code memory
was untouched, and once I had written sensible values back to the EEPROM, all
was ok.

Thanks for any ideas,
Simon.
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2002\08\01@142726 by Roman Black

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Simon Bryden wrote:
>
> I just had a weird case of EEPROM corruption on a 16F84. The first 14 words
> were overwritten to the value 0xAE during a thunderstorm which tripped the
> power.
>
> The thunderstorm is probably a red herring, and the power loss may be more
> likely to be a contender,

> Does anyone have any thoughts on what could have caused this? BTW code memory
> was untouched, and once I had written sensible values back to the EEPROM, all
> was ok.


Yes. :o) When the micro gets a BAD spike, ie current
through the die in either direction, it can corrupt
all registers including stack and program counter.
The little flip flops in the registers get flipped
and flopped, often towards the direction of the spike,
(which can be used to "force" ram in some cases)

If registers and PC etc could maybe contain trash or
even just a few trash bits, it could have jumped to
or otherwise entered your eeprom write routine. When
it go there with unknown crud in all the registers
it performed as well as it could and wrote *stuff* to
*somewhere* in eeprom.

Some of the micros can have bits set to 1's by hitting
them with a voltage spike. When we were teenagers I saw
a piezo spark igniter (reliably) clock up games on a
Galaga arcade machine, by zapping the main coin entry
plate it spiked the micro and instantly jumped the
"coins" variable from 0 to 99. I assume the spike set
the variable to all 1's (0xFF) and safety code trimmed
it to 99 for the 2 digit display. Sometimes the video
ram to the Z80 micro got hit and most of the screen
would go white. I was employed part time fixing these
machines and saw the results of deliberate spike attacks
regularly. :o)
-Roman

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2002\08\01@160321 by Josh Koffman

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Is this the basis behind the "glitch" removal of code protection?

Josh
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Roman Black wrote:

> Yes. :o) When the micro gets a BAD spike, ie current
> through the die in either direction, it can corrupt
> all registers including stack and program counter.
> The little flip flops in the registers get flipped
> and flopped, often towards the direction of the spike,
> (which can be used to "force" ram in some cases)

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2002\08\01@192136 by Lyle Hazelwood

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> Some of the micros can have bits set to 1's by hitting
> them with a voltage spike. When we were teenagers I saw
> a piezo spark igniter (reliably) clock up games on a
> Galaga arcade machine, by zapping the main coin entry
> plate it spiked the micro and instantly jumped the
> "coins" variable from 0 to 99. I assume the spike set
> the variable to all 1's (0xFF) and safety code trimmed
> it to 99 for the 2 digit display. Sometimes the video
> ram to the Z80 micro got hit and most of the screen
> would go white. I was employed part time fixing these
> machines and saw the results of deliberate spike attacks
> regularly. :o)
> -Roman

I remember this well.. There was an entire line of games
built with a similar motherboard. Simply rubbing your
feet on the carpet and touching the coin door was enough
to get you a free game. It also registered on the coin meter,
so the operator was left wondering where the quarters went.

Many fixes were tried. Sattellite boards were built to absorb
spikes at the main edge connector on the motherboard. They
were useless.
The "real fix" came by mixing a 50/50 solution of Downy fabric
softener and water. Spray the carpets once a month. No more
static, problem solved at the source.

I still use this trick to reduce static in the home and car. The only
change is that now it's "Ultra Downy", so the mix is more water
and less downy.

Lyle
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2002\08\01@234219 by Matt Pobursky

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On Thu, 1 Aug 2002 18:39:26 -0700, Lyle Hazelwood wrote: ...snip...
>Many fixes were tried. Sattellite boards were built to absorb spikes
>at the main edge connector on the motherboard. They were useless.
>The "real fix" came by mixing a 50/50 solution of Downy fabric
>softener and water. Spray the carpets once a month. No more static,
>problem solved at the source.
>
>I still use this trick to reduce static in the home and car. The only
>change is that now it's "Ultra Downy", so the mix is more water and
>less downy.

Great tip! I'm going to have to try that this fall/winter here as
static gets to be a big problem, even with a humidifier running full
time. It sure makes sense though, and should even make my house smell
nice... ;-)

Matt Pobursky
Maximum Performance Systems

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2002\08\02@010149 by Dale Botkin

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During fifteen-plus years as a field service engineer (IBM mainframes,
midrange, on down to PCs) I and every other FE used a LOT of this stuff.
Generally only used about 2-3 tablespoons of Downy liquid to a quart spray
bottle of water, though, it really doesn't take much.

Dale
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On Thu, 1 Aug 2002, Matt Pobursky wrote:

{Quote hidden}

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2002\08\02@055627 by Alan B. Pearce

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>During fifteen-plus years as a field service engineer (IBM mainframes,
>midrange, on down to PCs) I and every other FE used a LOT of this stuff.
>Generally only used about 2-3 tablespoons of Downy liquid to a quart spray
>bottle of water, though, it really doesn't take much.
>
>Dale

....

{Quote hidden}

I guess that is really what you have to do where there is a static
generating carpet present.

The other trick I have heard of is to have a pot plant put in the computer
room to act as a humidifier when the humidity was getting real low and
allowing static to cause corruption. But the example I heard of did not seem
to have carpet or some other floor covering as a specific generator of
static.

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2002\08\02@091608 by Olin Lathrop

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> The other trick I have heard of is to have a pot plant put in the computer
> room

Um, you might get into trouble if someone recognizes it.


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2002\08\02@093543 by Alan B. Pearce

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>> The other trick I have heard of is to have a pot plant put in the
computer
>> room

>Um, you might get into trouble if someone recognizes it.

yeah, that too, I was just telling some colleagues about a story related to
me by a previous colleague who had worked on an army base. One day they had
some police trainees around, so someone put a cannabis plant among some
other plants in the dining room. None of the police picked up on it, but it
disappeared before the "proper" authority came to remove it :)

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2002\08\02@101235 by Hazelwood Lyle

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> The other trick I have heard of is to have a pot plant put in the
computer
> room

This method may not lower static levels, but will certainly make problems like EEPROM corruption much easier to deal with.

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2002\08\02@110527 by Dale Botkin

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On Fri, 2 Aug 2002, Olin Lathrop wrote:

> > The other trick I have heard of is to have a pot plant put in the computer
> > room
>
> Um, you might get into trouble if someone recognizes it.

It will probably get defoliated occasionally too...

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