Modbus TCP


I 've readen some post but no response. I try to develop a soft to command an logic controler

The communication protocol is modbus TCP

Is somebody have class to communicate in modbus TCP or tips to make it

thanks in advance



I have used a C library on Github that provides support for Modbus TCP and EtherNet/IP. I have not used the Modbus TCP portion but the EtherNet/IP works very well with Rockwell ControlLogix PLCs. The Github URL is:

I’ve written a Xojo wrapper module for the library. You can get it at:
The wrapper is written for version 2.3 but it should work for the current 2.4 version. I usually put the dll file in the same folder as the executable.



Hello @Noel_Wetischek !

You’ll notice that whenever someone posts about Industrial Automation there are only a small handful of us that work in this industry, so the replies aren’t as rapid as on other topics.

I’ve done a great amount of programming for Modbus RTU, and it’s my understanding that Modbus TCP/IP is basically “Modbus RTU over IP”… or so I hear.

I’m overdue to look into this topic so I’ll start digging now and see if there isn’t some help I can offer.

Welcome to the Forum by the way!


Hi Noel,

I’m taking a look at the official spec on this (Modbus_Messaging_Implementation_Guide_V1_0b.pdf) and it’ll take me several reads to absorb and not fall asleep. I’ll also likely find some software that emulates a Modbus TCP/IP “Client” (formerly referred to as “Master”) that’s intended for use debugging “Server” nodes. And I’m headed out for a week holiday with family, so it’s unlikely I’ll have more to contribute to this thread till after the 29th of the month. However, I really do hope I can be of help. My company has a need to fully understand and work with this protocol - so it’s something I plan on sticking to. Best of luck for now!


This page, has a good listing of Modbus simulators. Worth checking out.

By the way, I confirmed my Xojo wrapper for the libplctag library (see my earlier post) does work with version 2.4 of the library. If you are on Windows, the 2.4 version is worthwhile since Windows performance has been improved.


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Thanks a lot Dennis and William

I’ll try your wrapper soon.

I have first to understand how to call/load the external library