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Modbus TCP through WR11

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I have been trying to connect a SCADA system to an Automation Direct PLC through a WR11 cellular modem using Modbus TCP. This same physical system was used previously with an OPC server that used a native protocol to connect to the PLC without issues. I had a port forwarded using the native PLC programming port (28784) and have now added a port forward using the default Modbus TCP port (502). What is interesting is if I initiate a connection from my local subnet to the PLC using the 28784 connection, then the Modbus connection works. It will stay working as long as I am connecting through 28784. If I stop using this connection method then the Modbus connection will work for exactly 40 minutes before dropping out. I suspect that it has nothing to do with the ports, but more the method. I have spent an unbelievable amount of time trying to make this work. Any thoughts would be appreciated.
asked Sep 12 in Digi TransPort Cellular by scwiebe New to the Community (0 points)

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