Thanks to everyone who replied. Sounds like this will be a "go" then. I didn't hear anyone hitting the brakes, so I'll give it a shot. Maybe I can even try out using Darrell's instant interrupts to get the quickest response.

Since the only purpose of the zero crossing detect is to turn on/off two sets of IGBTs, I intend to interface the mains directly to the PIC and let the internal clamping do its thing.

Now, I'll start looking for some code snippets to give me a place to start...

Should I use the "port change" feature in the PICs that offer that?

I was thinking that, simply, the first half "positive" side of the sine wave would be detected as "on" and the "negative half would be "off."

Now for the embarrassing newbie question: I understand how to detect an interrupt change, but how do I test whether voltage is swinging toward positive or toward negative (zero)? I assume capture/compare has something to do with it. I don't yet know how to do that, but it is time to jump in.

I hope that question makes sense.

Thank you all for your input.

Chris