用S7-200PLC的自由口模式和VB中的MSComm控件方便地实现了计算机与S7-200（CPU224）PLC的通讯。计算机作为主站,用户通过计算机可以方便地设置房间的控制指令并向PLC发出控制或监测命令， PLC作为从站来响应计算机发送的指令并采取相应的动作并将房间的电、水、热信息发回到计算机。用户可以通过电脑屏幕实时地监视到房间的电、水、热信息并进行相应的处理。-with S7-200PLC the Free Port Mode and the VB MSComm to realize a trap Computer and S7-200 (CPU224) PLC communications. Computer as a master station, Computer users can easily set up control rooms PLC issued directives to control or monitoring orders, PLC as from the station to respond to orders sent by the computer and take corresponding action will be room for electricity, water, Heat fat information to the computer. The user can screen real-time surveillance of the room electricity, water and heat information and handled accordingly.