If you’re using TCP-Com to connect a physical RS232 Serial port (a COM port) to a TCP/IP Port and you receive an error saying “COM Port is Unavailable,” then there are a few possible causes.
It could be that the COM port you’re trying to connect to doesn’t exist on the PC, or it could be that it’s already open by another application or another instance of TCP-Com. Windows does not allow more than one application program to open a COM port at the same time.
Check your PC’s COM ports
To check which COM ports you have installed in your PC, open the Windows Device Manager and look in the section labeled “Ports COM & LPT”. If the port that you are trying to open does not appear in the Windows Device Manager, then the port does not exist (you may have the wrong port selected) or the driver for the port has not been installed.
If the COM port you’re trying to use is a USB to RS232 adapter, and you do not see it listed in the Device Manager, then the driver for the adapter has not been installed correctly or it is not functioning correctly. In this case, you would need to contact the manufacturer of the USB to RS232 adapter to obtain the necessary drivers for the adapter.
Check if other apps or instances of TCP-Com are already using the COM port
If another application program has the COM port open, the solution is to close the other application program and try again.
Customers sometimes encounter an issue where multiple instances of TCP-Com are running and attempting to open the same physical COM port. For example, if you run a second instance of TCP-Com while the first is still running, the second instance won’t be able to access the same COM port because the first already has it open. This problem may not appear obvious because when TCP-Com is minimized, it appears in the System Tray instead of the Windows taskbar. Additionally, if TCP-Com is installed as a Windows Service or set to run “At Startup” as a Scheduled Task, it will run in the background without appearing in the Windows Taskbar.
If you suspect you have multiple instances of TCP-Com running, you can check for and shut them down with the Windows Task Manager. If you have installed TCP-Com as a Windows Service or created a Scheduled Task to run it at startup, we recommend uninstalling the Service or stopping the Task first. Then you can run TCP-Com.exe, edit and activate your configuration, quit the executable, and then reinstall the TCP-Com Service or restart the TCP-Com Task.Note – If you want TCP-Com to run automatically at startup for all logged on users, we recommend using the Windows Task Scheduler to create a scheduled task instead of installing it as a Windows Service. This gives you more flexibility and control.