Hello Amyfp,
You can use the DAQmx Connect Terminals VI to connect the 80 MHz Timebase to one PFI lines to which it is directly routed. These direct routes are listed in Measurement and Automation Explorer, by selecting the PCI-6602 under Devices and Interfaces >> NI-DAQmx Devices and then selecting the Device Routes tab (the bottom tab in the right-hand window), it looks like the 80 MHz Timebase can be routed to either PFI 2 or 6.
Let us know if you have any other questions.
Regards,
Micaela N
National Instruments