用51单片机I/O口模拟串口通信，在较低的比特率下能有较好的通信效果，尤其在单片机串口不够用时，模拟串口是很好的解决方法。-With 51 single-chip I/O port simulation of serial communications, at a lower bit rate to have better communication effects, especially in single-chip serial port when not enough to simulat