It isn't clear what exact role you intend those 2 signals to play in your measurement. Do you just want to count edges of one while using the other to set the timing for when you capture *samples* of those counts?
If so, check out the shipping example for "Counter - Count Edges (Finite Clock)". Or possibly the "Continuous" variety, depending on the answer below.
As to "Finite Mode", that will be defined by a specific # of samples, not a specific period of time. And the default behavior of a Read will be to *wait* for all those samples to accumulate before returning with them.
If you want 8 seconds worth of samples, regardless of how many that is:
1. Configure for Continuous Sampling, not Finite
2. In the call to DAQmx Timing, specify a "# samples per channel" that is easily at least 8 seconds worth. This will make your acquisition buffer big enough to hold all the data at once.
3. After starting the task and waiting 8 seconds, wire the special value -1 to DAQmx Read to specify "# samples to read". For a continuous sampling task, the -1 value means "give me all the samples available right now (that I haven't previously retrieved)".
Note that the same -1 value has a different special meaning for finite sampling tasks. There it means, "wait until the entire acquisition buffer fills up with samples, then return them to me."
I agree that some of this stuff is more confusing than it ought to be, hence this suggestion.
-Kevin P
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