After plugging in the USB to serial port, first check whether the serial port device appears in the device manager of the computer.

If there is no driver, there will be a question mark device. At this point, install the corresponding driver.

If the USB-to-serial device can be detected normally, then check whether the serial port is COM, and be careful that it is not necessarily COM 1.

Then select the corresponding COM number at the device port.

In addition, if the debugger uses COM port, then you can't use the serial debugging assistant to open COM.

A hardware serial port can only be used by one program at a time.