串口异步收发的有关问题

串口异步收发的问题
PC机和单片机通过串口通讯，PC机发送一个字符时，单片机会返回2个BYTE，手动点发送按纽
启动OnCommTXD时，PC机会收到数据，但自动调用WriteComm()函数时，却不能自动收到数据。
单片机没问题，收到一个字符，会立即发送数据。

DWORD WINAPI CC51Dlg::CommThread(LPVOID lpParam)

{

	CC51Dlg* dlg = (CC51Dlg*)lpParam;

	::SetCommMask(dlg->m_hCom, 0x05FF);

	DWORD dwReadBytes = 0;

	OVERLAPPED ol = {0};

	ol.hEvent = CreateEvent(NULL,TRUE,TRUE,NULL);

	DWORD dwEventMask = 0;

	while(1)

	{

		::WaitCommEvent(dlg->m_hCom, &dwEventMask, &ol);

		if (::WaitForSingleObject(ol.hEvent, INFINITE) == 0)

		{

			if (::GetOverlappedResult(dlg->m_hCom, &ol, &dwReadBytes, FALSE))

			{

				if (dwEventMask & EV_TXEMPTY)

				{

					dlg->m_bTX = TRUE;

				}

				if (dlg->m_bTX && (dwEventMask & EV_RXCHAR))

				{

					dlg->ReadComm();

				}

			}

		}


	}

	return 1;

}


BOOL CC51Dlg::WriteComm(char *pBuf, int nBytes)

{

	OVERLAPPED ol = {0};

	HANDLE hEvent = CreateEvent(NULL,TRUE,TRUE,NULL);

	ol.hEvent = hEvent;

	DWORD dwNumberOfWritten = 0;

	::WriteFile(m_hCom, pBuf, nBytes, &dwNumberOfWritten, &ol);

	if (!::WriteFile(m_hCom, pBuf, nBytes, &dwNumberOfWritten, &ol))

	{

		if (::WaitForSingleObject(hEvent, INFINITE) == 0)

		{

			if (::GetOverlappedResult(m_hCom, &ol, &dwNumberOfWritten, FALSE))

			{

				m_bTX = FALSE;

			}

		}

	}

	m_bTX = FALSE;/**/

	::CloseHandle(hEvent);

	return TRUE;

}


void CC51Dlg::OnCommTXD() 

{

	char str[8] = {0};

	::GetDlgItemText(m_hWnd, IDC_TXD, str, sizeof(str));

	WriteComm(str, 1);

}


BOOL CC51Dlg::ReadComm()

{

	OVERLAPPED ol = {0};

	HANDLE hEvent = CreateEvent(NULL,TRUE,TRUE,NULL);

	ol.hEvent = hEvent;

	DWORD dwNumberOfReaded = 0;

	WORD wBuf = 0;

	if (!::ReadFile(m_hCom, &wBuf, 2, &dwNumberOfReaded, &ol))

	{

		if (::WaitForSingleObject(hEvent, INFINITE) == 0)

		{

			if (::GetOverlappedResult(m_hCom, &ol, &dwNumberOfReaded, FALSE))

			{

				float fVoltage = 5 * (float)wBuf / 1024;

				char str[8] = {0};

				sprintf(str, "%0.2f", fVoltage);

				::SetDlgItemText(m_hWnd, IDC_VOLTAGE, str);

				char buf = 'A';

				WriteComm(&buf, 1);//这句好象不起作用

			}

		}

	}

	::CloseHandle(hEvent);

	return TRUE;

}

------解决方案--------------------
自动调用的地方估计有问题
------解决方案--------------------
串口线程调用WriteFile,一个字符瞬间发出,之后串口线程再调用WaitCommEvent,此时EV_TXEMPTY已经丢失了,你的m_bTX永远成不了真.

不用太严谨,发送一般不会出问题.EV_TXEMPTY只会把程序搞得更复杂,不用管它.