此原代码为RS232串口扩展器的主程序，也是基于单片机51系列，可将一个串口扩展为4个口子，并可控制各个口子的打开和关闭-The original code for the RS232 serial port expander for the main program, is also based on single-chip microcomputer 51, a serial port can be extended to four sources, and control all of the open and close the hole