AVR accidentally erased?

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I received a product of ours from a customer, which was defective. After
investigation it turned out that the AVR( an AT90C8515) in the product was
erased. When I tried to read the signature of the micro, 0x00,0x01,0x02 was
returned, which is normal for a locked device.
However, after erasing the AVR, it returned a signatue of 0xff,0xff,0xff. I
could however reprogram and lock the AVR after which the device operated

This device has been sitting on a boat and the customer said they had
overvoltage on the 12V grid, resulting in more defective equipment on board.
I'd rather think that this is the result of a lighting strike nearby, but
the behaviour of the AVR seems strange to me. Any opinions out here?
It seems that the signature is also factory programmed and the entire chip
got erased, instead of the program memory only.


Re: AVR accidentally erased?
Is the reset pin clamped, so that it can't exceed Vcc? I've seen cases where
a short transient exceeding the 12V needed to enter parallel programming
mode caused complete or partly erasing of AVRs. I've never worked with the
AT90C8515, though.
You may also look into Atmel's app note "AVR040: EMC Design Considerations"
which explains more details about this and similiar problems.


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Re: AVR accidentally erased?
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Yes, the reset is clamped. I followed that app note very closely with
regards to the reset input.


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