说明：  实时通讯方法的研究。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 PLC的 RS一232端口的串行硬件连接，然后通过对 S7—200系列 PLC进行通信编程 ，就可实现与上位机通信 。
(Real-time means of communication studies. PLC program in accordance with the definition of communication protocols (ie, PLC-frame format to receive information and definitions) to identify its information content. Through the PC s COM1 and S7-200 PLC s RS 1 232 serial port hardware connection, and then through the S7-200 series PLC to communicate programming, you can achieve with the host computer communications.)