How to trigger selected rows changed in one Drop Down to other Drop Down and reverse without looping

i need to block selected rows changed trigger. i have four Drop Downs, on first DD selection its selected value is passed to next DD on selected rows changed trigger, likewise it works for all four DD. now i want to do the same in reverse way i.e if last DD is called then its parent should automatically get populated. but here even if i populate its parent then the parent DD is row is getting changed and it automatically triggers selected rows changed for its child. goes in a loop. is there any way to block or stop selected rows changed trigger.