Decyphering Com Port Signals On Windows Xp

I have a legacy home automation system that is 17 years old. It is a Windows XP software program called Touchsoft and it controls all the devices in the house by way of signalling them through a RF dongle connected to com3 and transmitting on 868 Mhz. The devices are all switched by switches listening on RF 868. The people who wrote the software and suppled the hardware are all gone.
I have written a Python program to replace the Touchsoft software which runs on Windows 10 and I can connect the dongle to the computer that runs the Python program.
I have the Touchsoft program running and working properly ie switching the devices on and off on a XP computer.
The addresses of the devices are hidden in Touchsoft and I cannot find them. I know the command structure of the RF system from literature supplied 17 years ago.
My challenge now is to decypher the commands Touchsoft sends to com3 so that I can emulate them in the Python program. Please help.

 

https://docs.flipper.net/sub-ghz/read
Have you tried sniffing COM 3 when it is transmitting from the software to the dongle?
Is it a serial UART - 9 pin or USB to serial?

 

Thanks for the response. The dongle is plugged into a 9 pin serial port.
How would you sniff the port please.

 

I'm pretty sure I've seen software (Vovsoft & HHDsoft), but if you have another computer you can make something like a LAN tap but for serial. I can't find the wiring diagram I used, but look at this project here RS232 Serial Spy. If you want a device try Googling "Serial Ghost" - it is a tap with onboard memory. If you really have money to spend, the flipper will sniff the signals out of the air.