基于电话网的PLC与计算机远程通信

用电话网构成的分布式实时监控系统，上位机为工控机，下位机为S7—200系列PLC，采用PLC自由口通信．上位机利用VB 6．0MSComm通信控件，在Text中输入电话号码，调用ATD语句，通过Modem拔号，实现音频和脉冲上网，并接受其物理连接和数据持输的通信流程管理．PLC通信遵循MODBUS协议，支持RTU格式，数据交换类型由功能号控制，采用模块化结构．其通信调度模块判定通信出借，初始化模块进行工作区复位，寄存器刷新模块对寄存器实时刷新，控制命令接收模块接收上位机命令。

Remote Communication for PLC and Computer Based on Telephone Network

The real-time distributed supervision and control system based on telephone network is composed of industrial control Computer and PLC in S7-200 series, it adopts PLC free port communication. MSComm in VB6.0 was used in upper PC, as long as telephone number is input in Text, network browsing is realized with calling ATD sentence and modem dialing. The host can connect to PLC and transmit data to it and realize remote communication management. MODBUS protocol and RTU format is adopted in PLC communication, function numbers control the type of data switching. The modularization programming is used in PLC network, scheduler module determines whether communication make a mistake. Work area reposition is made with initialization module, refurbishing module real-time refurbish register, and command module receives command from upper PC.