[kamocat]

I was experimenting with the output speed and jitter, because I was considering using it as a simple tone generator.

I was having a lot of trouble with jitter, and so I finally tried a test that would just modulate a digital output as fast as possible. (before I had been regulating it with RT wait functions, in micro-seconds)
I found that it had a limit at about 280 micro-seconds to switch between the ON and OFF states.

In looking at the NI 9403 Operating Instructions, it says the module has a propagation speed of 330 nanoseconds, at maximum.
So why might I be seeing a limit 1000 times slower than that?
Is there some huge overhead that is slowing the processor down?
I've been deploying it as a startup application, so I know it's not because of any communications on the network.