[EricH]

Have you read the manual? Sorry to be so blunt, but that's the first thing you need to do if you haven't done so already. It sounds like you haven't.

As for whether you can use the NXT, I've traced the flowchart to the question, Is it an Additional Electronics component? If yes, and the cost is fine, you're good. If not, then you're not.

The next question is, what are you using it for? If you're using it to monitor battery voltage, I believe the cRIO has something that can do that for you. The answer to the "what are you using it for" can help figure out where to find the answers.

If you are using it for voltage/current monitoring, see <R44>. Also see all rules about custom circuits; the NXT would count as one.