Thanks a lot for replying. I do have the DSC module. I 'm a bit confused as regards how it all fits together.
What I have done previously was to use the 'Modbus library' functions & write out an app for conencting to the PLC's. This works fine though I have the task ( cumbersome ) of defining the Modbus commands, length of registers to be read etc & then use a shift register approach to switch between the MOdbus commands.
What I was hoping for in the Modbus I/O server was to be able to define all this during the creation of the I/O server & be absolved of it all later