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.