We have a Serial device here connected to the one and only COM port on the computer. The COM port is part of the motherboard (not an PCIe expansion card). In Windows Device Manager this com port shows up as COM1.

We have a device connected to this COM port, the device itself works on another computer and is connected correctly. However, it doesn't work on this pc and we would like to know if the COM port is physically broken.

Unlike USB Device the OS doesn't detect when a device is connected/disconnected.
How is it possible to test if the COM port is actually working when a device is connected to it.
Bonus: Also is it possible to test this without knowing the speed of the connected device?

  • 2
    You can check the COM port itself using a loopback test. You would need to short the transmit pin to the receive pin. This will work at any baud rate. The connection to the device requires proper configuration and the proper cable. A breakout box or oscilloscope are tools to solve connection issues. – sawdust May 28 '18 at 19:40
  • @PimpJuiceIT Thank you for your response. I might have mistyped my question. The device in question doesn't really matter. It's more about knowing if the COM port works. This way we can determine if the COM port or the device is broken. The question has been updated to include your remark. – user2827958 May 29 '18 at 14:21
  • Loopback test guide: ni.com/tutorial/3450/en Loopback adapter to make shorting the right pins easy: amazon.com/LINDY-60254-Serial-LoopBack-Connector/dp/B001FYY6PA – jejorda2 May 29 '18 at 15:17
  • Okay, great.... see what others suggest for validating if a COM port on a PC is broken or working properly or not. I never do that personally as I've never had issues with COM ports on machines like that and usually communication issues has been due to settings but I don't use COM ports on machines very often though either. If you have a known working machine with a known working COM port rather than the adapters, etc. you could try it too I suppose. Good luck regardless!! – Pimp Juice IT May 29 '18 at 15:51

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