use WriteFile to send buffer to COMM port error! --Urgent help!!!!!!!!!!!!!!!!!!!!!!!!!

Hi,all
    I want to write a char buffer to COM1 port, I write the code as below:

  //Step1 : open & init COM1 port
  hCom=CreateFile("COM1", GENERIC_READ|GENERIC_WRITE, 0, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL|FILE_FLAG_OVERLAPPED, NULL);
 if(hCom==(HANDLE)-1)
 {
  AfxMessageBox("Failed To Open COM1!");
  return FALSE;
 }

 SetupComm(hCom,1024,512);
 COMMTIMEOUTS TimeOuts;

 TimeOuts.ReadIntervalTimeout=MAXDWORD;
 TimeOuts.ReadTotalTimeoutMultiplier=0;
 TimeOuts.ReadTotalTimeoutConstant=0;
 TimeOuts.WriteTotalTimeoutMultiplier=100;
 TimeOuts.WriteTotalTimeoutConstant=500;
 SetCommTimeouts(hCom,&TimeOuts);

 DCB dcb;
 GetCommState(hCom,&dcb);
 dcb.BaudRate=2400;
 dcb.ByteSize=8;
 dcb.Parity=NOPARITY;
 dcb.StopBits=1;
 SetCommState(hCom,&dcb);

 PurgeComm(hCom,PURGE_TXCLEAR|PURGE_RXCLEAR);

 //Step 2: Send buffer to COM1 port
 OVERLAPPED m_osWrite;
 memset(&m_osWrite,0,sizeof(OVERLAPPED));
 m_osWrite.hEvent=CreateEvent(NULL,TRUE,FALSE,NULL);

 char lpOutBuffer[12];
 memset(lpOutBuffer,'\0',16);
 lpOutBuffer[0]=0x00;
 lpOutBuffer[1]=0x00;
 lpOutBuffer[2]=0x00;
 lpOutBuffer[3]=0x00;
 lpOutBuffer[4]=0x5F;
 lpOutBuffer[5]=0x5F;
 lpOutBuffer[6]=0x50;
 lpOutBuffer[7]=0x50;
 lpOutBuffer[8]=0x01;
 lpOutBuffer[9]=0xA1;
 lpOutBuffer[10]=0x8F;
 lpOutBuffer[11]=0x8F;

 DWORD dwBytesToWrite=12;
 DWORD dwBytesWritten;
 COMSTAT ComStat;
 DWORD dwErrorFlags;
 BOOL bWriteStat;
 ClearCommError(hCom,&dwErrorFlags,&ComStat);
 bWriteStat=WriteFile(hCom,lpOutBuffer,dwBytesToWrite,&
dwBytesWritten,&m_osWrite);

 if(!bWriteStat)
 {
  if(GetLastError()==ERROR_IO_PENDING)
  {
   WaitForSingleObject(m_osWrite.hEvent,1000 );
  }
 }

I use COM1 to send buffer and COM2 to receive buffer, the COM1 & COM2
setting are the same, but after I sent the buffer , I receive 15 bytes from
COM2 and the bytes content are different from those I sent from COM1, could
anybody tell me why?

Any helpful ideas would be highly appreciated!

-ja