Hi paulmw,
There isn't a function in the DAQmx API to query which terminals have already been connected. There are a couple of options to take into consideration here, although I won't jump to a conclusion as to which is best since I'm not too familiar with your application yet.
1.) You can disconnect all active routes by resetting your device, and this can be done programmatically. It may be a good idea to have this device reset occur at the beginning of your application's execution. At the bottom of this post, I've included a link to a KnowledgeBase article which shows how to do this programmatically.
2.) If the end user is specifying terminals to connect, you could implement some error handling to throw an error if the user tries to connect a terminal which is already part of an active route (i.e. return that error you've been receiving to the end user).
I'm guessing this is an application where either an end user or some automated process determines which terminals to connect? In general, I recommend disconnecting all of the connections you've made at the end of your application's execution--however, this could involve keeping a list of the active connections if there are going to be many of them which are determined programmatically.
How Can I Perform a Reset/Self-Test of My DAQmx Device Programmatically?: http://digital.ni.com/public.nsf/allkb/124D580AE300335E86256FDD006CE798
Tom D.
Staff Software Engineer
NI
