How to see modbus seril data coming from field devices to moxa CN2650I-16-2AC/EU terminal server by using wireshark ..thanks

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I haven't used the Moxa devices, but on most of the other similar devices I've used the device has an Ethernet port usually on the same network as the Scada system that can be used to capture traffic.

Usually, each physical serial port is mapped to its own TCP port so I've captured on the specific TCP port and obtained the required info.

Some other systems aren't so simple and require the installation of drivers on the Scada system to create virtual COM ports that map to the physical COM ports on the device. The network traffic then may not be plain TCP so you would then need a method of capturing serial traffic on the virtual COM ports which Wireshark doesn't handle out of the box. There may be an extcap plugin for Wireshark that could handle this, but I'm unaware of anything at the moment.