说明：  PLC程序根据定义的通信协议(即 PLC接收信息 帧的格式和定义 )识别其信息 内容,通过PC 的 COM1与S7-200
(The PLC program identifies the content of the information according to the defined communication protocol (that is, the format and definition of the PLC receive information frame), and through the COM1 of PC and the S7x200)