how to detect the zero crossing for an AC input signal

I want to determine time at every zero crossing for 5V AC input signal using the PIC micro-controller.in my search i found that I have to use interrupts to detect when the sine wave crosses zero. when interrupt will enable, timer will be start, it will run untill the interrupt become disable stop the timer and store time value in variable repeat this process continousely

I want measure the time taken the first crossing and store that value in variable then measure the time takan the...

how to detect the zero crossing for an AC input signal