Dave,
 Atmel had a problem with some of their AtMega chips. They recommended
that the first EEPROM location not be used. IIRC it could get
corrupted when the chip power supply died or glitched.

Have you tried using a different address?

RP


2009/9/30 David Duffy (AVD) <david@audiovisualdevices.com.au>:
> I have a design that uses a 16F88. The code is very similar to a few
> other products but they use a 16F628A or 16F648A.
>
> I'm having problems with this one design where in the field the EE is
> being erased. (I think) When I read the offending EE back (via MPLAB),
> the data is FF instead of its usual 00 .. 07 range.
>
> I've gone over the code numerous times and checked the write sequence. I
> can't even reproduce the fault back here. It can take days or months to
> show up in the field.
>
> I don't know if more than one location is being erased as I'm only
> storing and reading one byte. (the first one) Has anyone come across
> this before?
> David...
>
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