Advantage of the ZCD special PIC?

[hmmpic]

I can not see what the ZCD module can do better then a normal PIC with AD and OpAMP.

Anyone there can give a simple explanation on the advantage of using a pic with ZCD as 12f1612 have.

(Setup: ZCD signal is feed directly from AC-line to a CAP and a resistor, and two diode to clamp over end under voltage...)

[Ttelmah]

Nothing.

Point is it saves parts. The chip is being designed for simple applications that may well have to detect the mains phase, and every extra part costs space and money. Since most such applications will require a zero crossing detector, they include one. It's exactly the same answer as what the advantage is of the internal comparator. Answer, nothing, except removing the need to add a comparator to your circuit.

Beware of adding external diodes. Provided your series resistor is correctly chosen (so that even on the largest signals you expect, the current rating of the input pin current sink/source is not exceeded), the internal diodes do the job (they can withstand over 80* the current that is meant to be being delivered to the pin). Adding your own external diodes may skew the result, since the internal ZCD relies on the current all arriving at the input pin to correctly bias the voltage to the required point....
The diode (particularly on the 0v rail), can act to slightly bias the detection point.

[hmmpic]

Thanks for that:-)