串口读取数据不成功

打开串口函数成功
BOOL CSerial::OpenPort(LPTSTR lpszPortName)
{

DWORD dwError,dwThreadID;
if(hPort)
{
return FALSE;
}
//打开串口
hPort = CreateFile (L"COM2", GENERIC_READ | GENERIC_WRITE,
0, NULL, OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL|FILE_FLAG_OVERLAPPED,NULL);
//如果打开端口出错, 返回FALSE

if ( hPort == INVALID_HANDLE_VALUE )
{
//不能打开端口
CString strError;
strError.Format(_T("Unable to open %s, Error No.=%d"),
lpszPortName, GetLastError());
MessageBox (NULL, strError, TEXT("Error"), MB_OK);
return FALSE;
}
//指定端口监测的事件集
SetCommMask (hPort, EV_RXCHAR);
//分配设备缓冲区
SetupComm(hPort,1280,1280);
//初始化缓冲区中的信息
PurgeComm(hPort,PURGE_TXCLEAR|PURGE_RXCLEAR);
//配置串行端口
////////////////////////////////
DCB myDCB;
GetCommState(hPort,&myDCB);
myDCB.BaudRate = CBR_9600;
myDCB.fBinary = TRUE;
myDCB.fParity = TRUE;
myDCB.ByteSize = 8;
myDCB.Parity = ODDPARITY;
myDCB.StopBits = ONESTOPBIT;
SetCommState(hPort,&myDCB);
/////////////////////////////////
if(!InitDCB())
return FALSE;
//设置端口超时值
if(!InitCommTimeouts())
return FALSE;
//设置端口上指定信号的状态
// SETDTR: 发送DTR (data-terminal-ready)信号
// SETRTS: 发送RTS (request-to-send)信号
EscapeCommFunction (hPort, SETDTR);
EscapeCommFunction (hPort, SETRTS);

//创建一个从串口读取数据的线程

if (hReadThread = CreateThread (NULL, 0, ReadPortThread, this, 0,&dwThreadID))
{
}
else
{
//不能创建线程
MessageBox (NULL, TEXT("Unable to create the read thread"),
TEXT("Error"), MB_OK);
dwError = GetLastError ();
return FALSE;
}
m_bConnected=TRUE;
return TRUE;
}

读线程函数
DWORD WINAPI ReadPortThread(LPVOID lpvoid)
{

BOOL fReadState;
DWORD dwCommModemStatus;
DWORD dwLength;
COMSTAT ComStat;
DWORD dwErrorFlags;
CSerial *pOwner = (CSerial*)lpvoid;
char szBuf[1200];
memset(szBuf,0,1200);
OVERLAPPED Rol= {0};
while (hPort != INVALID_HANDLE_VALUE)
{
//等待串口的事件发生
WaitCommEvent (hPort, &dwCommModemStatus, 0);
if (dwCommModemStatus & EV_RXCHAR)
{
ClearCommError(hPort,&dwErrorFlags,&ComStat);
//cbInQue返回在串行驱动程序输入队列中的字符数
dwLength=ComStat.cbInQue;
n = dwLength;
if(dwLength>0)
{
//从串口读取数据
buf=szBuf;
ZeroMemory(buf,1200);
n = dwLength;
Rol.hEvent = CreateEvent(NULL,TRUE,FALSE,NULL);
if(Rol.hEvent == NULL)
{
AfxMessageBox(L"hEvent空",0,0);
return -1;
}
fReadState = ReadFile(hPort,buf,1200,&dwLength,&Rol);
n = fReadState;
n = dwLength;
if(!fReadState)
{
//不能从串口读取数据
MessageBox(NULL,TEXT("Error in read from serial port"),TEXT("Read Error"),MB_OK);
}
else
{
pOwner->DealData(szBuf,(int)dwLength);
}
}
}
GetCommModemStatus (hPort, &dwCommModemStatus);
}
return 0;
}

读线程函数在调用ReadFile返回值为0.
不知道错误在哪
查了很久了
忘大家竭力相助