Hi Fernando,
DAQ R2012a prerelease has added new functions that you can use to start your acquisition using an external trigger (digital pulse). If you have a valid licence you can download R2012a here.
You can modify the below code to suit your requirements:
s = daq.createSession('ni');
s.addAnalogInputChannel('Dev4', 0, 'Voltage');
The below command will add a external start trigger connection from an external source( i.e. your digital pulse) to the PFI0 terminal on Dev4.
s.addTriggerConnection('External','Dev4/PFI0','StartTrigger');
Your acquisition will now start when the device receives a digital rising edge at PFI0 terminal
s.startForeground();
Hope that helps,
Manisha
