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Problems with multiple masters accessing a V130 via Modbus TCP

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I have two redundant OPC servers that will need to access my V130 PLC simultaneously. I have setup two Modbus IP config and two Modbus IP SCAN_EX block with different Network ID and different ports (502 on socket 2 to Network ID 255 and 503 on socket 3 to Network ID 254).

Looks like it will only work when only one of the master is active. When both of the masters are active the last one to connect will not be able to connect.

Does anyone have a work around this? Do I need to only activate one SCAN_EX per scan cycle?

Thanks in advance


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  • MVP 2014

I haven't done this before (two simultaneous slaves) but I don't see why it wouldn't work. The following should be eliminated as possible problems.

When you say "connect" do you mean the TCP Socket Connect or the Modbus polling/acknowledgement?

I would say the Network ID fields on both configurations need to be 255.

Also double-check that your two SCAN_EX blocks are attached to different configurations.

You could try enabling them each on their own, as well as together and see what happens.

Also post your code, as that will help us find the most likely issues.

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  • 5 months later...
  • MVP 2023

I routinely code for systems with simultaneous multiple masters using MODBUS IP over Ethernet and Vision products. I've never had any issue even when the slaves are also masters to different PLCs. My systems get a bit complex due to the 4 socket limitation and I've created all kinds of crazy situations to shuffle data around to all parts of the system. One difference is that all my PLCs are always on the same subnet - I don't have any experience connecting across different subnets or across the internet.

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