Modbus and shared variable

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1

Hi everybody,

I’m using modbus for the first time with my cpu and I have a doubt.

My cpu is a modbus slave, I defined input registers where I mapped different variables and they are readable via modbus, everything is good.

I now need a “shared” variable, i.e. one value that can be read and write by both the cpu and the modbus remote server. I don’t understand if that’s possible or not, because if I map a variable to a holding register, the server is able to Read and Write, but my cpu is only able to Read it.

Is this normal?

Thanks

2

The dynamic channels option can’t be used as “shared” variables, you need to use the “Fixed buffer size” option to handle “shared” variables.

Automation Help: Modbus fixed buffer size

1 Like
3

ah ok I see. but in that case I can’t simply map variables from automation studio right?

4

You can’t map variables directly to the channels… but the channels themselves are already PLC variables.

5

ok i will look into it. thanks!