I'm speculating a bit based on what I remember from the product data sheet and from the documentation on the VIs in the driver. The 77xx is static digital. It goes high when you tell it to go high and stays high until you tell it to go low. If the pulse width option you're trying is the Configure Limit Output VI, then as the hlpe says, this is for the separate digital I/O port on the back of the instrument. I believe this works in conjuction with the Configure Limits function. If that's true, then the limit outputs will go active when the limit conditions are met. I don't have the instrument so you might want to double check the manual to see whether I'm correct.