PCIe-6602 measure edge separation between two square waves

Hello,

I have a PCIe-6602 and I wish to measure the edge speration of two quadrature wave forms from an rotary encoder.  Example: I watch for a transition of channel A. This transistion is can be either positive or negitive going edge. On the transistion the timer starts and then stops when the other channel, channel B sees a positive or negative transition.  This delta is the time that I am interestined in and that needs top be captured.

Thanks for help,

Mike Walczak