With large numbers of different mbeds the com port number can grow too high over time on a Windows PC and USB serial dies

03 Oct 2017

Our lab PC's mbed USB virtual com port stopped working after about a year. The issue was more than 256 different mbeds had been plugged into it, and com port numbers that high do not work in many terminal applications that use an auto fill drop down combo box to select ports. Putty still works since you can type in a com port number (after finding the number in device manager under ports) and there is a way to clear out all of the old com port assignments from previous mbeds.

In device manager our mbed com port is up to over 300 now!

Deleting, rebooting, and re-installing the mbed windows serial driver did not work in Win 7.

I found a post on one way to fix it and clear out the old com port assignments, but you need full admin: https://mcuoneclipse.com/2015/08/02/removing-hidden-com-lpt-ports-and-devices-on-windows/

Someone said this issue might go away with Windows 10, but I have not confirmed it.