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Modbus Periodic Read and Write


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Good morning to all

I am using a USC-X5-TR22 PLC on unilogic version 1.32.98 (attached image shows core of the issue)

my question is how does the modbus read/write  is executed? Does it read the registers every 200 millisecond? Does it read sequentially or concurrently?

If so, is it safe for me to have so many registers that I am reading?

Also from the attached image you can see that I have a number of modbus devices from which I am reading the same amount of registers.

This system is currently running, all I want to know is if it will stay that way.

Thank you for your responses

Unitronics modbus register.png

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  • MVP 2023

If everything works and reading speed satisfies you - leave everything as it is.

To reduce the number of consecutive read / write commands, you should try to read not each address separately, but a lot of sequentially placed data by one command. In your screen you can see consecutive registers from one device 9-11, 20-28, 14-16. If you look closely at each device, it is possible to read all the data from it with one command and only in the PLC to extract the necessary data from the received packet. This recommendation has been successfully applied in this topic


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