Hi TedWagner!
I've been looking into how we can do some sort of interupt in the DAQmx driver and from what I've found there are two methods of doing it. The majority of the functionality is contained in the specific hardware, Change Detection is only available on certain pieces of hardware, i.e. we can only enable change detection on a card that supports it at a hardware level, we cannot force a card that doesn't support it to do it at a driver level.
As your current device doesn't support change detection, you will have to set it up to poll the input whilst your other code runs. Then once it triggers it will run whatever code you include in that loop, so an emergency stop for example. This will take up resources on the host running this code, so mulithreadig would be ideal but like you said this could be overkill for this application. Unfortunately polling does seem to be the only option with the current hardware setup due to the nature in which the DAQmx driver works.
To sum up, we cannot force the driver to detect a change on the line unless the hardware specifically supports change detection (like the NI 6509). The only option available to you with your current hardware is to continuously poll one of the hardware lines in a loop (and perhaps in another thread) and then act with an if statement when a certain value is returned. Aplogies that it seems the driver cannot sepcifically act in the way in whihc you require, but the polling option is available as a solution to this.
If you have any more questions on this then let me know, hopefully the information above is sufficient.
Kind Regards,
Carlos O
Applications Engineer
National Instruments
