In measurement and control electronic products,it is often necessary for the main controller to provide multiple asynchronous serial port docking peripheral units.However,the on-chip serial port resources of the main controller are very limited,resulting in the scenario demand for serial port extenders.In this paper,WK2114 chip is used to design a four channel UART interface asynchronous serial port expander.The expander uses a standard 3-wire asynchronous serial port of the main controller to expand to obtain four enhanced sub serial ports.The chip has 256 level FIFO inside,and the baud rate,data bit length,and verification format of the sub serial port can be set separately.The maximum communication rate can reach 2 Mb/s.The functional verification and prototype test results prove that this extender has certain practical value.