Both constant-rate sampling and edge-detection based sampling would need ownership of the timing engine for the DI subsystem of the card. There's only one such engine available however, so you won't be able to do both at the same time.
Can your app be reworked to use just one of those sampling methods? For example, you can post-process your DI data from constant-rate sampling to do software-based change detection. Alternatively, you could rely primarily on change detection for sampling and perhaps add a counter task that can keep track of timestamps for those change detection events.
-Kevin P
CAUTION! New LabVIEW adopters -- it's too late for me, but you *can* save yourself. The new subscription policy for LabVIEW puts NI's hand in your wallet for the rest of your working life. Are you sure you're *that* dedicated to LabVIEW? (Summary of my reasons in this post, part of a voluminous thread of mostly complaints starting here).
