Raghu,

You don't need to get a derivative with a PCA. Why on the Earth to use a steam-hammer to crack nuts?

All of you need is to take only ATmega8515 chip and use its t/c1 input capture register! It can continuousely measure 1500 kHz during 1 millisecond period with 100 Hz accuracy (0.01%) @10 MHz crystal rate w/o interrupts. The interrupt you can use for displaying the 7-segment LED digit.

Regards,
George