I'm sure you've all at least had some interaction with Modbus, working in the automation industry. It's one of the most widely used protocols (if not the most widely used) in the world. Which is both its blessing and its curse, to some extent.
Given how long Modbus has been around and in use as an "open" protocol (starting in 1979), there have been many different interpretations of Modbus throughout the years. And with those different Modbus interpretations, much confusion about the different terminology for accessing data.
In this blog post, I will step through the basics of Modbus addressing including how offsets come into play, and how they affect what addresses to use in TOP Server for Wonderware applications.