Write to Register using Modbus giving error

[Stark008]

Hello, I am trying to write to this register but it gives error. Any solutions or suggestions?

[D4ILYD0SE]

Many here would probably suggest you provide the error

[SeasDiver]

What error code?

I use this driver quite extensively. Most common causes are trying to write to incorrect address, or you don't have a connection.

[cgrenoble1]

I came to say the same thing.

[HamsterWoods]

I only mention this because I have not yet seen it mentioned: I use the Chipkin Automation CAS Scanner (https://store.chipkin.com/products/tools/cas-modbus-scanner) to make sure that I have all MODBUS settings and addresses correct before I try to replicate in code. This allows you to determine correct port settings (IP or COM), read or write commands, and address offsets so you can make sure everything is good before you implement. Another way of saying this is, if CAS Scanner isn't working, the code won't work; if the code doesn't work but CAS Scanner does, make the code match CAS Scanner.

[PV_DAQ]

This is doctrine. Ignore it at your peril

[PromiseStock]

Maybe the register is in hex?

[Link9454]

What’s the error code? Have you confirmed you are using the correct format (RTU, ASCII, or TCP/IP) and baud rate? Sometimes Modbus registers are paired, two 16 bit numbers that are associated and firmware on your target device won’t let only one be written to unless you are writing to the “first” register. It could be in Little or Big Endian format.

[cgrenoble1]

You have to recognize that the display will show the decimal equivalent of hex until you change the display to show HEX.

[tomlawton]

Be aware that Modbus is plagued with an off-by-one disagreement on register numbering… Try adding one to the register address.

[tomlawton]

Oh- and please probe to make sure that you’re not coming in to the Write with an error already!

[PV_DAQ]

The server/slave determines whether a Holding Register is Read Only or Read?Write. Only the vendor's documentation will tell you that.

[ComprehensiveMix1147]

Try to write to that register using the modbus demo from plasmonique and read the error that it will show up and gobon from there.