Attempting to connect to multiple Modbus TCP devices (From S300)

Hi Folks,

I am attempting to use the Modbus TCP library on a S300 to cyclically talk to 3 different Modbus TCP devices - with very little luck.  I've been able to talk to one device at a time (1 or 3), but not all three cyclically.  My understanding is I need to call upon the modbuspn block and with updated parameters each query, but I can't quite get it right.  To make matters worse I have limited Siemens experience - I think I'm close but missing something minor (misunderstanding of the unit parameter? correct block interrogation?).  If someone could take a peak at my code and advise where I'm going wrong I would be forever great-full.

Code is in Step7 5.5 SP2

Thank you Wüstenräuber! With your guidance I was able to get it working correctly.