Inverter Connection via Profibus

I have a Siemens Simatic PLC 314C-2DP and I want to communicate this with two servo-inverters (LTi Drives) independently via Profibus connection. I have already used a routine (FC) that calls the appropiate System Functions of Step7 (SFC13, SFC14, SFC15) but unfortunately the servos moves with the same speed, same direction and same positioning as I have only one servo. If someone knows how can I solve this problem, please post me soon. Please note that is my first time that I use Profibus for such of this communication. Thank you in advance. Vasilis Papageorgiou.