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

From:

"ja" <josndrsn@yahoo.com>

Newsgroups:

microsoft.public.vc.language

Date:

Wed, 21 Feb 2007 22:07:42 +0800

Message-ID:

<u6XdpGcVHHA.5068@TK2MSFTNGP03.phx.gbl>

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