Moving into Modbus


Thread Starter


Hi experts,

I currently have a project that involves a Panasonic FP-x PLC and a Redlion G306 HMI to run a water treatment system. No problems there. What the client wants now is to have a number of these sites remote monitored through a website that they can login anywhere (mobile or at the office).

Due to the limitations of the internal webserver in the G306 we are now looking at using Modbus tcp to poll the data from the G306.

I think i understand the basics of Modbus tcp but would love for someone to explain the 'code' behind it and even if i'm on the right track choosing modbus. Appreciated much in advanced!
I have an open source / free software project that uses Modbus/TCP in a number of its programs. The web site for the project has a page which explains some of the basics behind Modbus/TCP.

This explains some other communications basics.

The Modbus spec can be downloaded from the Modbus organisation web site:

My software does (among other things) web based HMI. There is a soft logic control platform with integrated web based HMI:

There is also the same web based HMI in a stand alone version:

This section talks about the technology behind a web based HMI:

With any industrial web based HMI that I know of (including my own) you probably wouldn't want to put it directly on the Internet. You can have it on a VPN (virtual private network). Any competent IT specialist can set that up for you. If your own web site will be the Internet facing "front end" and handles all the security for this, then you might handle it that way as well.

I can't really go into any more detail than that however without knowing more about what the web application would do. People have used my software in similar applications (water treatment), but only as one component in a larger system. I'm not going to say at this point that it suits your application however since I don't know enough about what you are doing.

I am presently working on a new program that will convert between Modbus/TCP and a web service protocol that is meant to be used by typical PHP web applications. You would use conventional GET and POST from your PHP program to read or write field device values via Modbus/TCP. It's just a derivative of an existing program and I expect to have it done in a couple of days. If you are interested in that, let me know.

Also, if you want to discuss your application in more detail, then let me know and I will be happy to talk about it.