How can log the communication between my PC application and a COM port / RS232 device? How can I use Docklight to capture the communication to a Windows COM port (“COM port sniffer”)?

How can log the communication between my PC application and a COM port / RS232 device? How can I use Docklight to capture the communication to a Windows COM port (“COM port sniffer”)?

Applies to: Docklight and Docklight Scripting (all versions), Article ID: dl_faq049

Docklight does not have the ability to monitor serial port activity directly, like the classic “Microsoft Portmon” used to provide for Windows XP and earlier.

But here is how you can use a so-called Virtual Null Modem driver to re-route serial COM data through Docklight:

– Let’s assume your PC application is currently using COM1 to communicate with a RS32 device.
– Download and install the com0com v3.0.0.0 signed version software package from the link below.
– use the com0com “Setup” tool to add a new COM port pair, e.g. COM30 / COM 31.
– Configure your PC application to use COM30 (instead of COM1).
– In Docklight Project Settings… | Communication, set Communication Mode = Monitoring and use:
Docklight Channel 2 = COM1
Docklight Channel 1 = COM31 (2nd side of virtual null modem pair)
– Set other Docklight communication settings, e.g. baud rate, as required by your RS232 device.
– Start Docklight communication (F5).
– Start your PC application.
Now all serial communication from your application runs through Docklight and you can see both
data directions, you PC application side and the device’s responses.

NOTE: This approach by design will result in slightly different timing compared to the original direct communication.
In case timing is critical, you need to resort to hardware-based monitoring e.g. using our Docklight Tap Pro.

Null-modem emulator / com0com-3.0.0.0-i386-and-x64-signed.zip

Docklight Glossary – Virtual Null Modem

Docklight Project Settings – Communication