用PC机与多个51单片机通过RS232进行通讯。在多机通讯中，要保证主机与所选择的从机实现可靠的通信，必须保证串口具有识别的功能。在串行口控制寄存器SCON中

有一位叫做SM2，就是为了多机通讯而设置的控制位-Using a PC and a number of 51 single-chip RS232 communication. In multi-machine communication, to ensure that the host and the selected slave to achieve reliable communication, must ensure that the serial port has a recognition function. In the serial port control register SCON

One is called SM2, is to set the control bit for multi-machine communication