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When a Modbus COM port device is inserted in the tree, only static assignment of the parameters is possible.

If it is necessary for the assignment to be dynamic, then the complete handling must be implemented in the IEC code

Please note that the I/O Manager does not synchronize the different processes in the dynamic configuration.

This can cause the update behavior of the variables to differ from the static configuration, especially if it is accessed from several tasks.


  • Create a "Standard project" and select CODESYS Control Win V3 as the device.
  • Define the target system by means of the Network scan.



  • Open the Library Manager and add the Netzwork library.
    • IoDrvModbus
    • SysCom
    • SysTypes2 Interfaces



  • Adapt the POU PLC_PRG as follows:


    Declaration

    VAR
        xComPortOpen         : BOOL;
        xComPortError        : BOOL;
        rtsResult            : RTS_IEC_RESULT;
        stComPortSettings    : SysCom.ComSettings; 
        hComPort             : RTS_IEC_HANDLE;
    
        awReadBuffer         : ARRAY[0..31] OF WORD;        //note: adjsut to your requirements, max. is 128 Modbus Registers
        awWriteBuffer        : ARRAY[0..31] OF WORD;
        
        xExec                : BOOL;
        fbModbusRequest      : IoDrvModbus.ModbusRequest2;
        eComError            : IoDrvModbus.MB_ErrorCodes;
    END_VAR

    Implementierung

    IF(NOT xComPortOpen AND NOT xComPortError) THEN
        stComPortSettings.sPort := 3;
        stComPortSettings.byStopBits := 1;
        stComPortSettings.byParity := 0;            //EVEN:=2, ODD:=1 or NONE:=0*
        stComPortSettings.ulBaudRate := 19200;    //1200, 2400, 4800, ..., 115000 bps
        stComPortSettings.ulTimeout := 0;
        stComPortSettings.ulBufferSize := 256;    //Equals max size of Modbus packet
         
        hComPort := SysCom.SysComOpen2( pSettings := ADR(stComPortSettings), pSettingsEx := 0, pResult := ADR(rtsResult)); 
        
        xComPortError := (hComPort = RTS_INVALID_HANDLE OR rtsResult <> 0);
        xComPortOpen := NOT xComPortError;
    END_IF
    
    IF(xComPortOpen) THEN
        //apply new command
        fbModbusRequest.modbusCommand.uiFunctionCode := 23;        //Reda/Write Multiple Register
        fbModbusRequest.modbusCommand.uiReadOffset := 0;
        fbModbusRequest.modbusCommand.uiReadLen := 2;
        fbModbusRequest.modbusCommand.uiWriteOffset := 0;
        fbModbusRequest.modbusCommand.uiWriteLen := 2;
        
        fbModbusRequest.pRecvData := ADR(awReadBuffer);
        fbModbusRequest.pSendData := ADR(awWriteBuffer);    
        
        fbModbusRequest.tResponseTimeout := T#500MS;
    
        //note: if different tasks access the IO-Buffers then use some intermediate buffers 
        //      that are thread safe (use e.g mutex or semaphore) before calling the FB
        fbModbusRequest(
            hComPort := hComPort,
            xExecute := xExec,
            usiSlaveAddr := 2, 
            byModbusError => eComError);
    
        IF(fbModbusRequest.xDone) THEN
            //here you get valid data
            IF(awWriteBuffer[0] = awReadBuffer[0]) THEN
                ;
            END_IF
        ELSIF(fbModbusRequest.xError) THEN
            IF(eComError = MB_ErrorCodes.RESPONSE_TIMEOUT) THEN        //no cable plugged, wrong Com-Port settings ?
                ;
            END_IF
        END_IF
    END_IF


  • Start the project and test the functionality.

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