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'[EE]: 16F876 EEPROM Problems ** FIXED **'
2000\12\18@183224 by David Duffy

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Hi Richard,
Yahoo! You pinned it exactly. Now that you've pointed it out,
it all makes sense. I was setting EEDATA & EEADR for the
next byte while the EE was still busy doing its erase/pgm cycle.
I still pass the address in w but added a temp to put the data
into and I only update EEADR & EEDATA **after** my busy flag
goes low again. That little drama cost me a lot of time and the
simulator could not have showed it up either. Hey James, maybe
this is something to add somewhere on the piclist.com site?
Do you already have a page of gotcha's ?

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2000\12\18@185317 by David VanHorn

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At 09:35 AM 12/19/00 +1000, David Duffy wrote:
>Hi Richard,
>Yahoo! You pinned it exactly. Now that you've pointed it out,
>it all makes sense. I was setting EEDATA & EEADR for the
>next byte while the EE was still busy doing its erase/pgm cycle.
>I still pass the address in w but added a temp to put the data
>into and I only update EEADR & EEDATA **after** my busy flag
>goes low again. That little drama cost me a lot of time and the
>simulator could not have showed it up either. Hey James, maybe
>this is something to add somewhere on the piclist.com site?
>Do you already have a page of gotcha's ?


Remember also to have enough power to last you through a write cycle, and
to avoid being reset during one.  (Not sure in the pic, but a reset during
EEwrite is fatal in the AVR)


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2000\12\18@203221 by Bob Ammerman

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> Remember also to have enough power to last you through a write cycle, and
> to avoid being reset during one.  (Not sure in the pic, but a reset during
> EEwrite is fatal in the AVR)

What does "fatal" mean in this context?

Does the chip go up in smoke?

Is the location being programmed permanently damaged?

Is it indeterminate if the write completes?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2000\12\18@205338 by David VanHorn

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>What does "fatal" mean in this context?

Fatal to the write in progress.

>Does the chip go up in smoke?

No.

>Is the location being programmed permanently damaged?

No.

>Is it indeterminate if the write completes?

As far as power, not answerable. It would depend on when the lights go out,
and the previous contents vs the new contents.

Reset, I haven't tested. I suppose it would be simple enough.


There were big rumours about "eeprom corruption" in the AVR a while back.
Testing on my old silicon, it appears that the only real source for EEPROM
corruption was reset during write, or powerdown during write.

I did get it to corrupt once, by glitching the crystal, but I was never
able to replicate that. (glitching xtal while running code that was not
supposed to write to the eeprom)

I've been running one for over a month now, reading it's EEPROM, checking
for errors, through random powerdowns, resets, and even pulling the chip
from the socket while running.

I'm convinced that the AVR eeprom is as good as it ever gets for such devices.


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