用MSComm串口通信，为什么第一次发不过去呢？发第二次的时候就正常了。初学VB，求解释！！！

[zxl_cekong]

void __fastcall TForm1::Button7Click(TObject *Sender) //send
{
if(MSComm1->PortOpen==true)
{
MSComm1->Output=OleVariant(Edit4->Text);
//MSComm1->Output=OleVariant(Edit4->Text);
}

else
ShowMessage("请打开串口");

}
//---------------------------------------------------------------------------

void __fastcall TForm1::MSComm1Comm(TObject *Sender)
{
if(MSComm1->CommEvent==1)
{
OleVariant vRecStr=MSComm1->Input;
Edit5->Text=Edit5->Text+AnsiString(WideString(vRecStr));
//Edit5->Text=AnsiString(WideString(vRecStr));
}

}