VAR_INPUT
   slMode: SERIAL_LINE_MODE;
   udiPort: UDINT;
   udiBaudrate: UDINT;
   sbStopBits: COM.STOPBIT:= COM.STOPBIT.ONESTOPBIT;
   paParity: COM.PARITY:= COM.PARITY.EVEN;
   sWriteText: STRING:= 'AROR 0, 50';
   udiByteSize: UDINT;
END_VAR
VAR_OUTPUT
   sReadText: STRING;
   errError: COM.ERROR;
   xReadSuccess: BOOL;
   xWriteSuccess: BOOL;
   xClosed: BOOL:= TRUE;
END_VAR
VAR
   iState: INT;
   tTimer: TON;
   comOpen: COM.Open; (* Instance of the function block for opening a port *)
   hCom: CAA.HANDLE; (* handle of the port*)
   aParameter: ARRAY [1..7] OF COM.PARAMETER;
   comWrite: COM.Write;   (* Instance of the Write function  block *)
   bWriteBuffer: ARRAY [1..80] OF BYTE; (*Used to write data to the serial port*)
   szWrite: CAA.SIZE;
   comRead: COM.Read; (* Instance of the Read function block *)
   bReadBuffer: ARRAY [1..80] OF BYTE; (*Used to read data from the serial port*)
   szRead: CAA.SIZE;
   comClose: COM.Close; (* Instance of the function block for closing a port *)
END_VAR

CASE iState OF
   
   0:   // The parameter for the COM Ports are set
      aParameter[1].udiParameterId:= COM.CAA_Parameter_Constants.udiPort;
      aParameter[1].udiValue:= udiPort;
      aParameter[2].udiParameterId:= COM.CAA_Parameter_Constants.udiBaudrate;
      aParameter[2].udiValue:= udiBaudrate;      
      aParameter[3].udiParameterId:= COM.CAA_Parameter_Constants.udiStopBits;
      aParameter[3].udiValue:= sbStopBits;
      aParameter[4].udiParameterId:= COM.CAA_Parameter_Constants.udiParity;
      aParameter[4].udiValue:= paParity;
      aParameter[5].udiParameterId:= COM.CAA_Parameter_Constants.udiTimeout;
      aParameter[5].udiValue:= 0;
      aParameter[6].udiParameterId:= COM.CAA_Parameter_Constants.udiBinary;
      aParameter[6].udiValue:= 0;
      aParameter[7].udiParameterId:= COM.CAA_Parameter_Constants.udiByteSize;
      aParameter[7].udiValue:= udiByteSize;
      
      iState:= 1;
      
   1:   //First the COM Port is opened
      comOpen(xExecute:= TRUE, usiListLength:= SIZEOF(aParameter) / SIZEOF(COM.PARAMETER), pParameterList:= ADR(aParameter), hCom=> hCom);
      xClosed:= FALSE;
      IF comOpen.xDone THEN
         comOpen(xExecute:= FALSE);
         //depending on the mode the state for reading or writing is set
         IF slMode = SL_READ OR slMode = SL_READWRITE THEN
            iState:= 2;
         ELSIF slMode = SL_WRITE THEN
            iState:= 4;
         END_IF
      ELSIF comOpen.xError THEN
         errError:= comOpen.eError;
         comOpen(xExecute:= FALSE);
         iState:= 32767;
      END_IF
      
   2: //The reading process is started
      comRead(xExecute:= TRUE, hCom:= hCom, pBuffer:= ADR(bReadBuffer), szBuffer:= SIZEOF(bReadBuffer));
      IF comRead.xDone THEN
         szRead:= comRead.szSize;
         //check if the Port has send something
         IF szRead > 0 THEN
            //the text from the read buffer is saved in the sReadText variable
            MEM.MemMove(ADR(bReadBuffer), ADR(sReadText), UDINT_TO_UINT(szRead));
            MEM.MemFill(ADR(sReadText) + UDINT_TO_UINT(szRead), 1, 0);
            xReadSuccess:= TRUE;
         END_IF
         // the flag has to be set to false, that in the next cylce, the read task will start again, by setting it to true
         comRead(xExecute:= FALSE);
         iState:= 3;
      ELSIF comRead.xError THEN
         errError:= comRead.eError;
         comRead(xExecute:= FALSE);
         iState:= 32767;
      END_IF
      
   3: //After the reading process is finished, a timer is started for waiting 250 milliseconds
      tTimer(IN:= TRUE, PT:= T#250MS);
      IF tTimer.Q THEN
         tTimer(IN:= FALSE);
         xReadSuccess:= FALSE;
         IF slMode = SL_READWRITE THEN
            iState:= 4;
         ELSE
            iState:= 2;
         END_IF
      END_IF
      
   4: // the writing process is started
      IF NOT comWrite.xExecute THEN
         szWrite:= INT_TO_UDINT(LEN(sWriteText));
         //write the string to the buffer for the COM.WRITE Interface
         MEM.MemMove(ADR(sWriteText), ADR(bWriteBuffer), UDINT_TO_UINT(szWrite));
      END_IF
      comWrite(xExecute:= TRUE, hCom:= hCom, pBuffer:= ADR(bWriteBuffer), szSize:= szWrite);
      IF comWrite.xDone THEN
         // the flag is set to false, that in the next cyle this process is started again, by setting it to true 
         comWrite(xExecute:= FALSE);   
         xWriteSuccess:= TRUE;
         iState:= 5;
      ELSIF comWrite.xError THEN
         errError:= comWrite.eError;
         comWrite(xExecute:= FALSE);   
         iState:= 32767;
      END_IF 
      
   5: //After the writing process is finished, a timer is started for waiting 250 milliseconds
      tTimer(IN:= TRUE, PT:= T#250MS);
      IF tTimer.Q THEN
         tTimer(IN:= FALSE);
         xWriteSuccess:= FALSE;
         IF slMode = SL_READWRITE THEN
            iState:= 2;
         ELSE
            iState:= 4;
         END_IF
      END_IF
      
   6: //Closing the ports
      IF hCom <> 0 THEN
         comClose(xExecute:= TRUE, hCom:= hCom);
         IF comClose.xDone THEN
            comClose(xExecute:= FALSE);
            Fb_Init(FALSE, FALSE);
         ELSIF comClose.xError THEN
            errError:= comClose.eError;
            comClose(xExecute:= FALSE);   
            iState:= 32767;
         END_IF
      ELSE
         Fb_Init(FALSE, FALSE);
      END_IF 
   32767:
      ;
END_CASE

   FirstSerialLine(
      slMode:= SL_READWRITE, 
      udiPort:= 1, 
      udiBaudrate:= 9600,
      paParity:= COM.PARITY.NONE,
      sbStopBits:= COM.STOPBIT.ONESTOPBIT,
      udiByteSize := 8);