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MODBUS IP communication issue

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More than a question, this post is to share an workaround I found.

Visilogic 9.5.0

Modbus IP Master: V1210, using Socket 3, protocol UPD, port 502.

Modbus IP Slaves: Two V130, one V280.

Modbus IP time-out: #200 (2000 ms)

Modbus IP retries: 3

V1210 reads registers (Function 03) then write registers (Function 16) to each slave, waits a delay time to communicate (Read and write) with next slave (Delay between slaves=0.1 s).

After communicating with last slave, it waits a delay time (1.0 s) as a time between readings.

Everything works as it should only if all slaves are up and running. If any of the slaves is off (Off or disconnected from Ethernet network), V1210 lost communication with all slaves (Time-out(4) then no communication (5) in status message). It´s only possible to recover communications with connected slaves if delay between slaves is greater than 3 seconds. So, I set proper timer preset value based on communication status with each slave: 0.1 s if OK, 3.0 s if failed.

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Hi Gabriel,


Are you using UDP or TCP connection?

As you have only three slaves, you can use TCP connection. In the masster set three sockets as TCP master (Each socket will have its own MODBUS Config) and connect to the slaves.

In this configuration each slave is independent and if you will lose connection with one slave there will not be any delay with the others.

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