I don't understand why people trash AN521 so much. It simply shows a PIC 
interfacing to line voltage. It does not advocate human contact with the PIC when line 
connected. 

There are plenty of electronic devices in your world that are line connected. Compact 
fluorescent lights are electronic and line connected.

There are also methods to protect devices and humans if component failure 
happens. Two resistors in series is a widely used and accepted practice.

Moving to a second topic, in the United States and in all countries I know of, a certain 
amount of line current is allowed to flow through human beings. A VCR, for instance, 
although isolated, has a resistor and capacitor from neutral to case. Neutral and hot 
frequently get reversed, but the amount of current that would flow into a grounded 
human when this happens is small, acceptable, and legal.

I'm all for safety, don't get me wrong. But if someone is building something that 
controls line power, such as the triac control mentioned in AN521, he/she needs to 
take precautions building it and fiddling around with it. It doesn't matter whether 
there's a PIC in it or not. You don't need to stop designing it when you decide to put a 
PIC in it.

Thirdly, as far as applying higher than supply voltages to inputs of a PIC, there are 
PICs and there are PICs. The amount of current you inject, and what polarity it is, will 
affect operation at different levels depending which PIC you choose. The 16C54 
allows 500uA without affecting operation. As new PICs have been introduced, that 
value has decreased but is still nonzero, especially if you are not using analog 
features in the PIC.

I hope I have made this clear enough that readers will not think I am starting a flame 
or religious war.

Cheerful regards,

Bob

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