about FB

If I call FUNCTION BLOCK multiple times, do I have to create each different instance DB?

 For each FB that is called, you intended a different ,unique and specific task.This is the reason that you need to assign a unique instance DB(IDB) for each instance of calling that DB.

Consider you use an FB to control some valves and you assigned DB700 to control XV5001, you need to use a different DB (e.g DB701) to control XV5002. The reason is to avoid mixing up tasks and avoid chaos in control algorithm.

I hope it helps,

hdhosseini