I would like to control & monitor Plant operations directly from different field IOs to a common modbus TCP/IP common gateway. I want to implement ladder logic/control logic as real time java program and communicate to the field using this modbus tcp/ip gateway. Please suggest the best method and application protocol.

 

I have an open source software project called MBLogic.
http://sourceforge.net/projects/mblogic/

That can give you the following features built in:

1) Modbus/TCP server (slave).
2) Modbus/TCP client (master) connections that lets you open up simultaneous client connections to multiple field devices.
3) Web based graphical HMI.
4) Soft logic (PLC) system.
5) Web based system monitoring and control.
6) Web based on line help.

It uses Python rather than Java, but if you don't need to know anything about Python in order to use it. You program the logic control in instruction list (a ladder editor is currently under development). If you aren't interested in the soft logic or HMI features, you can ignore them and use the system as just a Modbus/TCP gateway.

Your Java program could communicate with MBLogic by two means.

1) Your Java program could act as a Modbus/TCP client (master) and talk to the Modbus/TCP server (slave) in MBLogic. There are a number of Modbus/TCP libraries available for Java. Here are a few (I don't know enough about any individual one to make a recommendation):

http://sourceforge.net/projects/jamod/
http://sourceforge.net/projects/modbus4j/
http://sourceforge.net/projects/jmodbus/

2) Your Java program could talk to MBLogic by using the HMI server protocol. This is a web service protocol using JSON. The protocol is quite simple and is fully documented.

MBLogic would act as an I/O server gateway which scans the field devices using Modbus/TCP. Your program could then read and write the data to MBLogic using one of the two methods outlined above. If you have any more questions, let me know and I will be happy to answer them.