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private void button1_Click(object sender, System.EventArgs e)
{
	this.richTextBox1.Focus();
	SendKeys.Send("{BACKSPACE}");
}

using System.Windows.Forms;

private void button1_Click(object sender, EventArgs e)
{
this.richTextBox1.Text = this.richTextBox1.Text.Remove(this.richTextBox1.TextLength - 1, 1);
}

const
  GUID_CLASS_COMPORT: TGUID = (
    D1:$86e0d1e0; D2:$8089; D3:$11d0; D4:($9c, $e4, $08, $00, $3e, $30, $1f, $73));

procedure EnumPortsWdm(AList: TStrings);
var
  LGuid: TGUID;
  LDeviceInfo: HDEVINFO;
  LDevice: TSPDevInfoData;
  LDeviceInterfaceData: TSPDeviceInterfaceData;
  LDeviceInterfaceDetailData: PSPDeviceInterfaceDetailData;
  LSuccess, LIsUsbDevice: Boolean;
  LDeviceInterfaceDetailDataSize,
  LRequiredSize: DWORD;
  LIndex: DWORD;
  LFriendlyName: array[0..255] of Char;
  LDesc: array[0..255] of Char;
  LLocInfo: array[0..255] of Char;
  LComPortInfo: TComPortInfo;
begin
  ClearPortsList(AList);

  LGuid := GUID_CLASS_COMPORT;
  LDeviceInfo := SetupDiGetClassDevs(@GUID_CLASS_COMPORT,
    nil, 0, DIGCF_PRESENT or DIGCF_DEVICEINTERFACE);
  if (Cardinal(LDeviceInfo) = INVALID_HANDLE_VALUE) then
  begin
    Exit;
  end;  
  SetupDiGetDeviceInterfaceDetail(LDeviceInfo,
    @LDeviceInterfaceData, nil, 0, @LRequiredSize, @LDevice);
  LDeviceInterfaceDetailDataSize := LRequiredSize;
  GetMem(LDeviceInterfaceDetailData, LRequiredSize);
  try
    // This is required, according to the documentation. Yes,
    // it's weird.
    LDeviceInterfaceData.cbSize := sizeof(TSPDeviceInterfaceData);
    LDeviceInterfaceDetailData.cbSize := sizeof(TSPDeviceInterfaceDetailData);
    // Enumerate the serial ports
    LIndex := 0;
    while True do
    begin
      if not SetupDiEnumDeviceInterfaces(LDeviceInfo,
        nil, LGuid, LIndex, LDeviceInterfaceData) then
      begin
        Break;
      end;
      LDevice.cbSize := sizeof(TSPDevInfoData);
      LDevice.ClassGuid := GUID_CLASS_COMPORT;
      // Got a device. Get the details.
      if not SetupDiGetDeviceInterfaceDetail(LDeviceInfo,
        @LDeviceInterfaceData,
        LDeviceInterfaceDetailData,
        LDeviceInterfaceDetailDataSize,
        @LRequiredSize, @LDevice) then
      begin
        Break;
      end;
      // Got a path to the device. Try to get some more info.
      LSuccess := SetupDiGetDeviceRegistryProperty(LDeviceInfo,
        LDevice, SPDRP_FRIENDLYNAME, nil,
        PByte(@LFriendlyName[0]), sizeof(LFriendlyName), nil);
      LSuccess := LSuccess and SetupDiGetDeviceRegistryProperty(
              LDeviceInfo, LDevice, SPDRP_DEVICEDESC, nil,
              PByte(@LDesc[0]), sizeof(LDesc), nil);
      LIsUsbDevice := FALSE;
      if SetupDiGetDeviceRegistryProperty(
              LDeviceInfo, LDevice, SPDRP_LOCATION_INFORMATION, nil,
              PByte(@LLocInfo[0]), sizeof(LLocInfo), nil) then
      begin
        // Just check the first three characters to determine
        // if the port is connected to the USB bus. This isn't
        // an infallible method; it would be better to use the
        // BUS GUID. Currently, Windows doesn't let you query
        // that though (SPDRP_BUSTYPEGUID seems to exist in
        // documentation only).
        LIsUsbDevice := (Pos('USB', LLocInfo) = 1);
      end;
      if LSuccess then
      begin
        LComPortInfo := TComPortInfo.Create;
        LComPortInfo.DevPath := PChar(@LDeviceInterfaceDetailData.DevicePath[0]);
        LComPortInfo.FriendlyName := LFriendlyName;
        LComPortInfo.PortDesc := LDesc;
        LComPortInfo.IsUsbDevice := LIsUsbDevice;
        AList.AddObject(LFriendlyName, LComPortInfo);
      end;
      LIndex := LIndex + 1;
    end;
  finally
    FreeMem(LDeviceInterfaceDetailData);
    SetupDiDestroyDeviceInfoList(LDeviceInfo);
  end;
end;