Well, there is a need for the communication between M340 PLCs. Because of that, I use NOE module. It has I/O scanning. M340 doesn't need to communicate with S7-300. SCADA on both PCs has to read/write them all. I still don't have type of Citec, this is just block scheme for a project I work on. First I need to know my equipment demands and than will somebody connect everything together.