serial interface

i write a monitoring program and i need to read permanent the rs232 port i must receive 4 byte data
on com1. I write fallowing code fragment for initialisation the com1 and send and receive function
but when i send 4 byte data sometimes its ok sometimes not and when i will receive data i receive
everytime 2 byte or 3 byte, what can be wrong with my code,
i send a command message packet to a targetsystem and must wait for answer, how can i synchronize
send and receive sequence, the target system need time to execute the command(about 400 ms).

                 thank you

void MainFrame::OnDeviceSerial()  /*initialisation the serial interface*/
{
 
   
        COMMCONFIG com;
      COMMTIMEOUTS cto;
     
      int ans;
      CString cst;
    CString dw_par;
      CString cw_par;
      CString si_par;
      HANDLE hdl;
      ans=0;
      DCB dcbp;
       MONITORINGApp*  mainapp;
       mainapp=(MONITORINGApp*)AfxGetApp();
     hdl=mainapp->hcomm;
      
       lk = CommConfigDialog( "COM1",GetSafeHwnd( ),&com);/* show the Serial interface dialog for COM2*/
       if(hdl==0){
       hdl=CreateFile("COM1",GENERIC_READ|GENERIC_WRITE,0,NULL,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0);/*open com2 for read and write*/
       }
       if(GetLastError()==ERROR_INVALID_HANDLE) AfxMessageBox("INVALIDE HANDLE");
       memset(&cto,0,sizeof(cto));/* init timeout structur for com2*/

      // cto.ReadTotalTimeoutMultiplier=1; /****125*4=500 ms time for read operation*/
      
       cto.WriteTotalTimeoutMultiplier=1;
       SetCommTimeouts(hdl,&cto);/*set timeouts */
       com.dcb.DCBlength=sizeof(com.dcb);
       DCB dcb3=com.dcb;
       GetCommState(hdl,&dcb3);
       SetCommState(hdl,&com.dcb);/*set the com parameter*/
     GetCommState(hdl,&dcbp);/*get the com parameter*/
     comok=1;
      }

================================================
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BOOL transfer::send_msg()
{
BOOL mark;
BOOL send_ok;      
int byte_count;
byte_count=0;
send_ok=false;      
//fwritestat=WriteFile(APPT()->hcomm,&write_buffer,bytes_to_write,&bytes_writen,&oswrite);
      for(int m=0; m<4; m++){
            ::Sleep(50);
            fwritestat=WriteFile(APPT()->hcomm,&write_buffer[m],1,&bytes_writen,&oswrite);
            if(bytes_writen) byte_count++;}
      if(bytes_to_write==(DWORD)byte_count) send_ok=true;
      if(!fwritestat)
      {
            if(GetLastError()== ERROR_IO_PENDING)
            {
                  while(!GetOverlappedResult(APPT()->hcomm,&oswrite,&bytes_writen,TRUE)){
                        dwError=GetLastError();
                        if(dwError==ERROR_IO_INCOMPLETE)
                        {
                              dw_bytes_sent+=bytes_writen;
                              continue;
                        }
                        else{
                              ClearCommError(APPT()->hcomm,&dwerrorflag,&comstat);
                              break;
                        }
                  }
          dw_bytes_sent+=bytes_writen;
              if(dw_bytes_sent!=bytes_to_write) return(FALSE);
            }else{
                  ClearCommError(APPT()->hcomm,&dwerrorflag,&comstat);
                  return(FALSE);
            }
      }
if(send_ok) mark=true;
if(!send_ok) mark=false;      
return(mark);
}



int transfer::receive_msg(LPSTR lpszBlock, int nMaxLength)
{
BOOL fReadStat;
COMSTAT ComStat;
DWORD dwErrorFlags;
DWORD dwLength;
DWORD dwError;
//char szError[10];
OVERLAPPED osRead;
ClearCommError(APPT()->hcomm,&dwErrorFlags,&ComStat);
dwLength=min((DWORD)nMaxLength,ComStat.cbInQue);
if(dwLength>0)
{
      fReadStat=ReadFile(APPT()->hcomm,&lpszBlock,dwLength,&dwLength,&osRead);
      if(!fReadStat)
      {
            if(GetLastError()==ERROR_IO_PENDING)
            {
                  while(!GetLastError()==(APPT()->hcomm,&osRead,&dwLength,TRUE))
                  {
                        dwError=GetLastError();
                        if(dwError==ERROR_IO_INCOMPLETE)
                              continue;
                        else
                        {
                              ClearCommError(APPT()->hcomm,&dwErrorFlags,&ComStat);
                              break;
                        }
                  }
            }
            else
                  dwLength=0;
            ClearCommError(APPT()->hcomm,&dwErrorFlags,&ComStat);
      }
}

rec_data=lpszBlock;

 return(dwLength);

}