实现PC机与单片机间的串口数据通信修改的回调函数-Serial data communication between PC and MCU modify callback

unicom这个的protel的电气图，上位机与单片机的通讯电路图，很难得，大家可以参考下-unicom the electrical diagram of protel, PC and single-chip communication circuit, so hard, we can refer to the next! ! !