I'm developing an USB driver for an embedded device, which appears to Windows as a CDC (virtual COM) device. I'm using Free Serial Port Monitor and Realterm to interact with the device.

Whenever I reset the device the COM port effectively disappears from the system, even though it may be "open" by these utilities. When the device is restarted the COM port re-appears in Device Manager, as expected. However, neither Free Serial Port Monitor or Realterm can find it. My suspicion is that the port is somehow locked.

I need a tool for observing any locks on COM ports and a way of unlocking the port, short of rebooting the computer, which I've been doing (very time consuming). Does such a utility exist?


Disabling the device in Device Manager, and then re-enabling it, freed the device for use.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.