Oops, my bad. I should have checked the module type first. In your case, the information in my other post applies that I posted just yesterday in this same forum. I have attached a test vi that generates 20,000 samples per second and updates the signal (duty cycle if you wish) every 500ms. I wrote it for a 9401 module in a 9184 chassis, but I think it'll work the same for the 9403 module.
The code isn't pretty (one of the loops doesn't even have a way to be stopped, ha), but you'll get the idea of how to do the digital write.
Douwe
