According to my actual application (win7 system environment), after installing the driver correctly, only USB serial port is displayed, not com. It should be that the value of the virtual com port is already the maximum, and the system will not automatically clear it and start numbering again.

The solution is to clear the data of com slogans. Run win+r, enter "regedit" and enter the registry. Then enter HKEY _ local _ machine \ system \ current control set \ control \ communication name arbiter. At this time, we can find the numerical item: ComDB, whose value represents the serial number currently used. At this point, you should be able to see that the value is fffffff ... directly select this ComDB and delete it. Reconnect the device and a com slogan should be displayed.