2 dropdowns dependent on each other

I am trying to create 2 dropdowns that are dependent upon each other. 1 is department (so they can look up by dept number) another is department description (can look up by dept desc).

What I need:  [LIST=1]
[*]With SuiteScript 2.0 I need to create the dept description dropdown.[LIST=1]
[*]It doesn't need to show any options until a subsidiary has been selected.
[*]The first option should always be blank until dept or dept description is selected.
[*]I need to put it right after or below the department.
[/LIST]
[*]With both being dependent upon each other, I need to not get in an infinite loop in the fieldChanged. So if dept changes desc I don't need desc to try and change dept, and then dept to change dept desc again (infinite loop of fieldChanged).