Answer: It is recommended that the driver software for the USB to serial debugging tool is correctly installed under the operating systems XP and WIN7. If the host computer prompts that there is no available serial port, you need to check whether the USB debugging tool has installed the matching driver software and whether the communication cable is well connected. You can also plug and unplug the USB port again and open the serial port manually to test, if the scroll bar below the upper computer scrolls normally, it means the communication is good.