Hi Neil,

One of the ways people do to try to break code protection on PICs is
quickly glitch the power supply. It can make the program counter change
without the chip resetting. So I bet you have an EEPROM write in your
code somewhere, and since you have no bulk capacitance you can get quick
glitches in the power supply, and then the program counter changes to
your EEPROM write routine. But since all that changed was the program
counter, who knows where or what gets put into it.

Also you might consider doing all on-the-fly writes to EEPROM in
triplicate, and doing majority rule on reads from those locations. That
way if the chip resets when writing, at worst you have is old data. But
you still need to add some capacitors to your power supply.

Best regards, Bob


On Sun, Oct 26, 2014, at 05:17 PM, Neil wrote:
> Hi all,
>=20
> Have a product working very well for a long time on the bench, but in a=20
> truck I'm getting EEPROM data corruption.  Only real difference is the=20
> power source.  Is this possible?  I switched to an external EEPROM and=20
> haven't tested on the truck yet, but thought I'd ask in the mean while.
>=20
> My power supply is fairly basic --  reverse protection diode, small=20
> resistor, 8V regulator, then 5V regulator.  0.1uf caps on the input and=20
> output of the regulators.  Total current draw is 60mA.
>=20
> Cheers,
> -Neil

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