Purchase requisitions in MRP run

Hi ,

When MRP is run for the total plant , MD01,what should be the control parameter for create pur req ?.

I checked by altering the control parameters for MRP run(MD01). When MRP is run with option 1 (in create pur. req) it creates pur requistion and when run with option 3, it creates planned order.

In the plant there are raw material as well as semi finished products. So when MRP is run for the total plant what control parameter should be used ?

Regards

ShankarR