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 and did not receive, you can continue to send, receive a response until the send date. Forward this program is 20 times the number of threshold.