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procedure TForm1.Button1Click(Sender: TObject);
begin
OpenCOM(1);
SetBaudRate(9600);
SendString(PChar('#rme'+chr(1)));
CloseCOM;
end;					

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procedure TForm1.Button2Click(Sender: TObject);
begin
OpenCOM(1);
SetBaudRate(9600);
SendString(PChar('#rme'+chr(2)));
CloseCOM;
end;					

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procedure TForm1.Button3Click(Sender: TObject);
begin
OpenCOM(1);
SetBaudRate(9600);
SendString(PChar('#rme'+chr(0)));
CloseCOM;
end;					

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unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)

  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

  // Benutzte GlobaleVariablen
  PortTimeout : _COMMTIMEOUTS;
  PortHandle : Integer;
  PortDCB : TDCB;
  PortNr  : Integer;
  PortState : Cardinal;
  WriteOverlapped,ReadOverlapped,StatusOs: TOverlapped;

implementation

// Testen ob Schnittstelle verfügbar ist
function ComAvailable(ComNr: byte): boolean; stdcall;
var
  TestHandle : integer;
begin
  TestHandle :=
  CreateFile(PChar('\\.\COM'+IntToStr(ComNr)),GENERIC_READ or GENERIC_WRITE,0,
             nil,OPEN_EXISTING,FILE_FLAG_OVERLAPPED,LongInt(0));
  if (TestHandle <= 0) then
    Result := false
  else
  begin
    Result := true;
    CloseHandle(TestHandle);
  end;
end;

// Ini Funktion für die Overlapped Strukturen
procedure InitOverlapped(var Overlapped : TOverlapped);
begin
  Overlapped.Offset := 0;
  Overlapped.OffsetHigh := 0;
  Overlapped.Internal := 0;
  Overlapped.InternalHigh := 0;
  Overlapped.hEvent := CreateEvent(nil,True,False,'');
end;

// Die Schnittstelle öffnen / schließen / testen
function OpenCOM(Port: byte): boolean; stdcall;
begin
  PortHandle :=
  CreateFile(PChar('\\.\COM'+IntToStr(Port)),GENERIC_READ or GENERIC_WRITE,0,
             nil,OPEN_EXISTING,FILE_FLAG_OVERLAPPED,LongInt(0));

  if PortNr > 0 then
  begin                                     
    Result := true;
    InitOverlapped(WriteOverlapped);
    InitOverlapped(ReadOverlapped);
    InitOverlapped(StatusOs);
  end else Result := false;
end;

// Die Schnittstelle konfigurieren
function SetBaudRate(baud: cardinal): boolean; stdcall;
begin
  GetCommState(PortHandle,PortDCB);
  PortDCB.BaudRate := baud;
  Result := SetCommState(PortHandle,PortDCB);
end;

function SendString(Str: PChar): boolean; stdcall;
var
  written  : cardinal;
  tmpStr : string;
  i: LongBool;
begin
  if (PortHandle <> 0) then
  begin
    tmpStr := string(Str);
    Result := not WriteFile(PortHandle,tmpStr[1],Length(tmpStr),written,@WriteOverlapped);
  end;
end;

// COM Schließen
procedure CloseCOM; stdcall;
begin
  PurgeComm(PortHandle, PURGE_RXABORT or PURGE_RXCLEAR or PURGE_TXABORT or PURGE_TXCLEAR);
  SetCommMask(PortHandle,0); //unterbricht WaitCommEvent im Polling thread
  CloseHandle(PortHandle);
  PortHandle := 0;
end;

{$R *.dfm}					

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function SendString(const Str: String): boolean;
var
  written  : cardinal;
begin
  if (PortHandle <> 0) then
    Result := WriteFile(PortHandle,Str[1],Length(Str),written,@WriteOverlapped) else
    Result := False;
end;					

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SendString('#rme'+chr(0));