用控件spcomm写的上位机程序

我先用上位机给单片机发数据，单片机接收到数据后在发给上位机并显示出来．问什么上位机接收不到单片机发给的数据，怎么知道上位机已经给单片机发数据了．我的单片机程序好用我已经用串口助手调试过了，谢谢
unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, SPComm;type
  TForm1 = class(TForm)
    Memo1: TMemo;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    Button5: TButton;
    ComboBox1: TComboBox;
    Label1: TLabel;
    Button6: TButton;
    Comm1: TComm;
    Edit1: TEdit;
    procedure Button3Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure Comm1ReceiveData(Sender: TObject;Buffer:pointer;BufferLength:Word);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;
implementation{$R *.dfm}procedure TForm1.Comm1ReceiveData(Sender: TObject;Buffer:pointer;BufferLength:Word);
var
data:string;
begin         //接收数据
SetLength(data,BufferLength);
move(Buffer^,pchar(data)^,Bufferlength);
Memo1.lines.Add(data);
Memo1.Invalidate;end;
procedure TForm1.Button3Click(Sender: TObject);
begin
Form1.Close;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
comm1.StopComm ;
button1.Enabled:=true ;
end;procedure TForm1.Button1Click(Sender: TObject);
begin
try
//comm1.CommName:='com'+inttostr(combobox1.ItemIndex);  //选择端口号
comm1.CommName=com1;
comm1.BaudRate:=9600;
comm1.StartComm;
button1.Enabled:=false;
button2.Enabled:=true;
button3.Enabled:=true;
button4.Enabled:=true;
button5.Enabled:=true;
   except
      ShowMessage('打开串口错误!');
end;
end;procedure TForm1.Button4Click(Sender: TObject);
var
str:string;
begin             //发送数据
str:= Edit1.Text;
form1.comm1.writecommdata(pchar(str),length(str));
end;
end.