实现STC12系列双串口单片机的串口转发。其实现了串口转发后如果另一边设备因为忙而没有收到，可以再继续发送，直到发送收到应答为止。此程序转发次数门限为20次。-Achieve STC12 Series Dual serial microcontroller serial port forwarding. After the realization of the serial port forwarding as if the other side of the device is busy an