单片机直接进行双机通讯程序；由于当发送中断发生的时候、接收中断发生的时候。中断号都是4，都会进入中断子程序，这里就通过if(RI===1)很巧妙的解决了这个问题。也就是说，只有接收中断发生后才会执行if内部的程序。(A single chip computer directly carries out a two machine communication program; because when the interrupt occurs, the receiving interruption occurs. The interrupts are all 4, and they all go into the interrupt subroutine, and this is a very clever solution to the problem by if (RI===1). In other words, only after the interrupt is received will the program within the if be executed.)