The most straightforward way I'd recommend is to share a sample clock from a master DIO task that all the other tasks use, *and* make sure the master task is started last.
Configure (but don't start) the master task with it's "normal" sample clock, and let's just say the master task is on "Dev1". To let DAQmx handle all the routing, drop down a DAQmx Timing property node and read the property Sample Clock-->Terminal. Wire that to the all the other tasks' DAQmx Timing.vi as the sample clock "source" signal. (I generally also query and wire up the sample rate). You can start the other tasks right away and they won't do any sampling until they get sample clock signals after you start the master task.
There are ways to route the sample clock signal explicitly to a specific PXI backplane trigger line, but it's usually simplest to let DAQmx manage such things automatically behind the scenes.
-Kevin P
ALERT! LabVIEW's subscription-only policy came to an end (finally!). Unfortunately, pricing favors the captured and committed over new adopters -- so tread carefully.
