Modbus Conformance

Modbus_ConformanceIf you’re a device manufacturer and you’ve ever developed an EtherNet/IP Adapter, BACnet/IP Server or a ProfiNet IO Slave device, you are cognizant of conformance testing. These organizations are sticklers for making sure that products are not released to the market without validating that they have the minimal required functionality. This is very typical of most industrial protocols. Most trade organizations specify a protocol test that has to be successfully executed to get a certification statement or logo that a device vendor can use to indicate that the device conforms to the specification of the technology.

This is, of course, extremely important to a lot of very big, very important customers like automotive manufacturers. They don’t want to spend their time sorting out the whys and wherefores about why product X doesn’t work well with product Y. In fact, it’s absolutely the last thing in the world that they want to be doing. They want to buy a certified product specifically so they won’t be fighting that battle. They know that there is high probability that your certified product is going to perform correctly in their application.

Modbus has been a little late to this party. For a lot of years, there was no conformance test for Modbus products. A developer would create something, test it in some fashion, and ship it. It was left to the user to figure out what worked and what didn’t work.

In the time since, the Modbus Organization has remedied this problem. They not only established a test procedure, they contracted with the University of Michigan to implement it. You now have two options for certification of your Modbus Slave device or Modbus TCP Server device.
One, you can self-certify. That means that you download the test and execute it yourself. You pledge that your product meets the minimum functionality of a Modbus device as specified by the test.

Two, you can purchase testing from the Modbus Organization. The test lab at the University of Michigan will perform the test for you and validate your device. That, of course, is going to cost you some cash and some time. But you get a second set of eyes and third party testing.
You can find out all about testing, including what tests to perform and what options are available, by visiting the Modbus Organization certification web page at

If you visit that site, you will notice that only your Slave or Server device can be tested. There is no test for Master or Client devices. The Controller side of many programs cannot be certified through the trade organization’s test facility.

You will also note on that site that only Modbus TCP Server devices can be tested. The Modbus Conformance test is designed for Modbus TCP Ethernet devices, not Modbus Serial devices. To test a Modbus RTU Serial device, you must use a gateway that can connect your Modbus Serial device to a Modbus TCP Client. Any Modbus Router can be used for the test, but the Modbus Organization recommends a product from Schneider Electric. I recommend the BFR3000, the router from Real Time Automation. Yes, that’s a shameless plug, but what do you expect from me?


PS – A couple of cool links for you: Royalty Free Modbus TCP Server Source code and Royalty Free Modbus TCP Client Source code. You may also get a free copy of my book by sending me a message using the following link: