The best professional soft in this direction is Serial Port Tester by Eltima(
rs232 tester). It benefits are:
1)Collect and record data. Can connect even to a COM port already open by any application to start sniffing it right away.
2) Has a unique functionality of monitoring several COM-ports simultaneously.
3) Read captured data in different ways. There are 4 view modes to present recorded serial data – table, line, dump and terminal.
4) Terminal mode feature enables simulate sending data to serial ports.
5) Full support for Modbus RTU and Modbus ASCII protocols.
6) Unique session playback possibility - you can send data received from the app to the serial port again. This way you can review port’s behavior on receipt of the same data for more precise monitoring results. Also you can compare sessions with automatic display of differences between them.
https://www.youtube.com/watch?v=yaLb5XyYTLM