Don’t forget there’s an issue involving Big Endian and Little Endian conversion of floating point numbers. I seem to recall posting about that issue with some feedback on using unions that helped me solve the problem. And yes, there is some confusion regarding register addressing. I found a modbus simulator that helped me debug my code since I did not have an actual modbus device handy for testing. It also allowed me to specify my own numbers in registers so I absolutely knew what data was expected.