说明：  hdlc协议指导,HDLC链路控制协议来源于IBM,目前广泛应用于嵌入式仪器仪表中,是最实用的通信规程.你或许还不知道你已经使用其中的方法.
(hdlc protocol guide, HDLC link control protocol from IBM, now widely used in embedded instrumentation is the most practical communications protocols. you may not know that you have to use one method.)