The corresponding serial port number could not be found. The USB virtual serial port realized by the national MCUSDK can be recognized under WIN 10, but not under WIN7, so the corresponding serial number cannot be found, and an accessory driver can be installed to solve it. USB virtual serial port belongs to the category of USB communication equipment. In the physical layer, a physical serial port is provided for the host through a USB bus in the form of a virtual serial port. IN the system, the USB controller provides an in endpoint and an OUT endpoint for batch transmission, which are used to receive and send data, and simulate the RX and TX lines of the serial port.