I have used 2 x 510k in series and 1nF to ground into PIC pin from 220 V
mains. The PIC did not use AD. With AD I'd use my clamping circuit. This
configuration (with 1Meg and 1nF) should resist 2kV spikes if and only if
the resistors have proper voltage rating. This was not in a production
circuit and it violates input voltage specs (go below and above gnd and
vdd by more than 0.3V). Nominal protection diode current is 310uA (220V
country). There is a 5V1 zener across the PIC power pins, which is also
the only voltage regulator this circuit has got. The PIC was 16F84 for
prototyping then 12C508A.

Peter

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