Hi Vijayganesh (I promise I'll never make fun of Raghunathan again),

Unless you're using a special case, such as a derivative with a built in ADC, and particularly if you are putting a signal into a port pin, your signal should only be one of the two logic levels (lo or hi) appropriate for your derivative. The data sheet will specify the particular logic levels your derivative will handle, but I'd be surprised if it won't handle a hi of 5V (and lo will be 0V). While these input signals switch between these two levels, they are still DC voltages (the current doesn't change directions and the voltage doesn't go negative except within the limits of overshoot toleration).

It sounds like you are new to µ-controlers. If so, I recommend that you read the tutorials found on the left hand menu bar. Also, read the Bible from Philips. Erik will post the links for you, or you can do a search for "Bible" and you'll find them in about a buh'jillion posts (that's a whole lot, as opposed to just a half lot).