Newbie needs help with Modbus


Thread Starter


I have two Sullair air compressors with supervisor controllers. I've been asked to archive all sensor data from them. I found a box sold by Millie Research that converts the supervisor controller protocol to Modbus. Where do I go from here? I know a few languages (C, Java, RPGIV/LE). I'm guessing that C will be the most useful, but I don't even know where to start! Can I download a Modbus header file somewhere and maybe a PDF tutorial? Any help will be greatly appreciated.

Fred Loveless

Depending upon what you need to get the data into you could just use and exisitng OPC/DDE Server to connect to the converter and serve the data to a client application.

Kepware's KEPServerEx OPCDDE Server ( and its Modbus Driver Suite can do this connectivity. You can try the full functioning demo for free. Any questions? Contact Kepware Technical Support ([email protected])

If you still wish to develop the interface your self you can download the Modbus protocol from

Fred Loveless
Support Manager
Kepware Technologies
The simplest way is to collect with a prewritten application that is already written with Modbus protocol. Kepware produces an OPC Modbus server (Kepserver) that is very simple to use it comes with C and VB sample code. Once you are using OPC, you can easily connect to the OPC server software from other remote PCs. They will provide a demo on request that you can try before you buy.


Curt Wuollet

You can download sample code at Or at least you could last time I looked.



Darrin Hansen

You could also check out Sullair's eConnect embedded web server product. It supports Modbus/TCP for accessing all connected supervisor data, logs all supervisor and physical IO data for 7 days, and nightly sends out XML report emails among other things. You can also import log file data directly from the unit into Microsoft Excel, where there is a standard .XLS file that lets you plot the data as a 3D surface chart, etc.

Sullair has a ASCII port where the data can be colected without additional hardware. Allthough the compressor will be required, to be set in the broadcast mode.

Then use an ASCII server like Omni Server, to colect data. Altough the ascii server will require some insight on how the protocall works Sullair has a sequencing manual that explains this.
Automated Solutions offers several off-the-shelf Modbus products that can be used to build your data logging app.

Modbus Class Library for use in c++.

Modbus ActiveX Control for use in most ActiveX Control containers (VB, .NET, VC++, MSOffice, etc.)

Modbus OPC Server for use with any OPC Client application including off-the-shelf data loggers.