I can’t read (or write to) my Modbus/TCP device OR the data I get from my Modbus/TCP device doesn’t make sense. What’s wrong?

Modbus/TCP devices, though based on a standard protocol, may be set up differently from one another. Some use zero-based addressing and some use one-based addressing. Some devices don’t support all Modbus functions. Modbus/TCP devices also vary in the way they present float data. And device documentation sometimes doesn’t specify how the device is set up.

If you’re having trouble reading or writing to your device, or if the data is clearly wrong, start by reading the sections "Modbus Protocol Settings" and "Data Interpretation Settings" in the groov Build and View User's Guide. Consult your device’s documentation for help, and change the settings for your Modbus device in Configure > Devices and Tags. You may need to try different combinations of settings to see what works.

If data from the Modbus device doesn’t make any sense (looks like garbage or is completely abnormal), change the "Use base one addressing" setting. Or change the combination of Data Interpretation Settings.

Probably the best way to figure out how to connect with any Modbus/TCP device and get the data presented in the right format is to use a Modbus/TCP test utility, like ModScan32 from www.Win-Tech.com. Our Product Support Group recommends this utility.

You can also use the utility Wireshark (www.wireshark.org) to see the Modbus/TCP traffic between your devices, so you know exactly what message was sent and what the specific reply was.

If you need help, be sure to contact Opto 22 Product Support. Product support is free.