Your small caps have power supply holdup times in the order of a few
milliseconds. If no spikes that drop out the supply completely are longer
than this you may be getting noise induced by other means. But without a
more detailed look I'd not be at all surprised if direct supply dropout was
the poblem. At that stage your PIC may be surviving brownout internally
with its reset and disable mechanisms, but if you cannot guarantee the
voltage-time profiles on the external eeprom pins it is on its own.

For a controller's internal brownout mechanism to protect externally
connected parts it must guarantee the relative state of all interconnected
pins on the potentially affected device, AND the device itself must
guarantee that it can survive  a multi transition brownout on the power
rails and any other pin that is not guaranteed by the PIC.

If the EEPROM spec says it will survive random violence on its supply lines
and any other non-PIC-connected pins, if the PIC connected pins are managed
well, AND if the PIC guarantess that it will not only survive said violence
but guarantee the state of the interconnected pins during that period, then
all may be OK. If both of those guarantees are not specifically given then
you have no reason to be certain that corruption should not occur.
Should-not and will-not are variably well correlated in reality :-).



    Russell
--=20
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