Hi,
after discussion with a engineer from NI I understood the meaning of the tirgger in this kind of board.
Actually the trigger just waits that a signal comes on the analogic port after a clock front. If it arrives after the front it waits until the next one.
My purpose was to do somthing else. As my signal arrives randomly on the analogic port I need to say to the card to do the acquisition at the right moment with a defined delay.
This is possible actually with the external clock and the trigger. The external clock will allow to change the internal clock and allows with the right delay to do acquisition.
Now I understand why nobody was able to answer because the question was not pertinent and I did not use the right vocabulary.
Does the moderator can close this disscussion, because my pb is now reseolved.
best
Anouchah