工控上位机如何和西门子PLC通信

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S7协议是西门子私有协议。基于OSI模型

因为平时对S7协议研究不多，所以直接使用第三方的DLL， Snap7

这次用的第一个，win32的dll，需要声明引入

    public class Snap7
    {

        [DllImport("Snap7.dll")]
        public static extern int Cli_Create();
        [DllImport("Snap7.dll")]
        public static extern void Cli_Destroy(int Client);
        [DllImport("Snap7.dll")]
        public static extern int Cli_ConnectTo(int Client, string Address,int Rack,int Slot);
        [DllImport("Snap7.dll")]
        public static extern int Cli_SetConnectionParams(int Client, string Address, int LocalTSAP, int RemoteTSAP);

        [DllImport("Snap7.dll")]
        public static extern int Cli_Connect(int Client);
        [DllImport("Snap7.dll")]
        public static extern int Cli_Disconnect(int Client);

        [DllImport("Snap7.dll")]
        public static extern int Cli_DBRead(int Client,int DBNumber,int Start,int Size,int Buffer);
        [DllImport("Snap7.dll")]
        public static extern int Cli_DBWrite(int Client, int DBNumber, int Start, int Size, int Buffer);

        [DllImport("Snap7.dll")]
        public static extern int Cli_ErrorText(int Error, string Text, int TextLen);
    }

使用方法也特别简单, 第1步，启动程序时先创建一个对象

int Client = Cli_Create()

第2步，连接到西门子plc的IP

int Result = Cli_ConnectTo(Client, "192.168.0.1", 0, 1)  //插槽1if(Result ==0)  //连接成功{cmdConnect.Enabled = False；cmdClose.Enabled = True；} ShowResult (Result)

第3步，读写PLC， 例如DB220.DBB10读1位

Result = Cli_DBRead(Client, 220, 10, 1, Buffer)

Result = Cli_DBWrite(Client, 220, 10, 1, Buffer）

第4步，退出程序时，销毁对象

Cli_Destroy (Client)