Hi,
I am trying to have an OperatorPanel with softPLC to communicate with external I/O. I want to use CoDeSys for det communications between OP and the external I/O.

I want to use Modbus. How is this possible? I just learned that ModBus TCP isn't for free - are ModBus RTP?

 

The Modbus spec is open and anyone can write a driver. However, the CoDeSys vendor is in business to make money and will likely charge money for drivers (and everything else).

I don't know what "RTP" is, so I can't answer that question.

Here is some information on Modbus/TCP.
http://mblogic.sourceforge.net/mbapps/ModbusBasics-en.html