[Beginner] In my calling vi there is a sub vi which is basically a while loop with many loops and structures inside it. I want to start and stop the sub vi from the calling VI only. But the while loop in the sub vi only takes the first value from the control on main vi. essentially the first pic is a dummy of the sub vi ( with all the structures inside it removed) and of the calling vi. the sub vi should only start if the initial value of boolean is true. please help

Either pass the reference as mentioned, or transfer data through Events (in which case you pass the event register thread instead) or my favorite, an Action Engine (AE). In the last case your main vi writes data to an AE and the sub-vi reads from it. I think Ben has an excellent nugget on AEs. /Y