SITOP USV , USB in Delphi

Dear Sirs,
it's my first time working with create-, write- and readfile, and I'm not able to contact the SITOP USV via the USB.
I'm using Delphi 6 under WinXP.
Is there anyone who can correct this source?

var
Form1: TForm1;
usv:THandle;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
usv:=CreateFile(PChar('USB\VID_0403&PID_E0E0.DeviceDesc="SITOP DC-USV 6"'),GENERIC_READ or GENERIC_WRITE,FILE_SHARE_READ or FILE_SHARE_WRITE,NIL,OPEN_EXISTING , FILE_ATTRIBUTE_NORMAL, NULL);

end;

procedure TForm1.Button2Click(Sender: TObject);
var
Freceivetext : String[20];
Fread : DWORD;
Fover : POverlapped;
begin
ReadFile(usv , Freceivetext , 20 , Fread , FOver );
Memo1.Lines.Add(Freceivetext);
end;

procedure TForm1.Button3Click(Sender: TObject);
var
schicken:string;
Fwritten:DWORD;
Fover:POverlapped;
begin
schicken:='R';
WriteFile(usv,schicken,1,Fwritten,Fover);
end;


Is it necessary to close the handle?

Thank you.
Jens Jung