工業控制領域(如DCS系統),經常涉及到串列通信問題。為了實現微機和單片機之間的數據交換,人們用各種不同方法實現串列通信,如DOS下採用彙編語言或C語言,但在Windows 環境下卻存在一些困難和不足。在Windows操作系統已經佔據統治地位的情況下(何況有些系統根本不支持DOS如Windows2000)開發Windows 環境下串列通信技術就顯得日益重要。 VC++6.0是微軟公司於1998年推出的一種開發環境,以其強大的功能,友好的界面,32位面向對象的程序設計及Active X的靈活性而受廣大軟體開發者的青睞,被廣泛應用於各個領域。應用VC++開發串列通信目前通常有如下幾種方法:一是利用Windows API通信函數;二是利用VC的標準通信函數_inp、_inpw、_inpd、_outp、_outpw、_outpd等直接對串口進行操作;三是使用Microsoft Visual C++的通信控制項(MSComm);四是利用第三方編寫的通信類。以上幾種方法中第一種使用面較廣,但由於比較複雜,專業化程度較高,使用較困難;第二種需要了解硬體電路結構原理;第三種方法看來較簡單,只需要對串口進行簡單配置,但是由於使用令人費解的VARIANT 類,使用也不是很容易;第四種方法是利用一種用於串列通信的CSerial類(這種類是由第三方提供),只要理解這種類的幾個成員函數,就能方便的使用。筆者利用CSerial類很方便地實現了在固定式EBM氣溶膠滅火系統分區啟動器(單片機系統)與上位機的通信。以下將結合實例,給出實現串列通信的幾種方法。 1 Windows API通信函數方法 與通信有關的Windows API函數共有26個,但主要有關的有: CreateFile() 用 “comn”(n為串口號)作為文件名就可以打開串口。 ReadFile() 讀串口。 WriteFile() 寫串口。 CloseHandle() 關閉串口句柄。初始化時應注意CreateFile()函數中串口共享方式應設為0,串口為不可共享設備,其它與一般文件讀寫類似。以下給出API實現的源代碼。
1.1 發送的常式 //聲明全局變數 HANDLE m_hIDComDev; OVERLAPPED m_OverlappedRead, m_Over lappedWrite; //初始化串口 void CSerialAPIView::OnInitialUpdate() { CView::OnInitialUpdate(); Char szComParams[50]; DCB dcb; Memset(&m_OverlappedRead, 0, sizeof (OVERLAPPED)); Memset(&m_OverlappedWrite, 0, sizeof (OVERLAPPED)); m_hIDComDev = NULL; m_hIDComDev = CreateFile(“COM2”, GENERIC_READ│GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL│FILE_FLAG_OVERLAPPED, NULL); if (m_hIDComDev == NULL) { AfxMessageBox(“Can not open serial port!”); goto endd; } memset(&m_OverlappedRead, 0, sizeof (OVERLAPPED)); memset(&m_OverlappedWrite, 0, sizeof (OVERLAPPED)); COMMTIMEOUTS CommTimeOuts; CommTimeOuts. ReadIntervalTimeout=0×FFFFFFFF; CommTimeOuts. ReadTotalTimeoutMultiplier = 0; CommTimeOuts. ReadTotalTimeoutConstant = 0; CommTimeOuts. WriteTotalTimeoutMultiplier = 0; CommTimeOuts. WriteTotalTimeoutConstant = 5000; SetCommTimeouts(m_hIDComDev, &CommTimeOuts); Wsprintf(szComparams, “COM2:9600, n, 8, 1”); m_OverlappedRead. hEvent = CreateEvent(NULL, TRUE, FALSE, NULL); m_OverlappedWrite. hEvent = CreateEvent(NULL, TRUE, FALSE, NULL); dcb. DCBlength = sizeof(DCB); GetCommState(m_hIDComDev, &dcb); dcb. BaudRate = 9600; dcb. ByteSize= 8; unsigned char ucSet; ucSet = (unsigned char) ((FC_RTSCTS&FC_DTRDSR) != 0); ucSet = (unsigned char) ((FC_RTSCTS&FC_RTSCTS) ! = 0); ucSet = (unsigned char) ((FC_RTSCTS&FC_XONXOFF) ! = 0); if (!SetCommState(m_hIDComDev, &dcb)‖ !SetupComm(m_hIDComDev,10000,10000)‖ m_OverlappedRead. hEvent ==NULL‖ m_OverlappedWrite. hEvent ==NULL) { DWORD dwError = GetLastError(); if (m_OverlappedRead. hEvent != NULL) CloseHandle(m_OverlappedRead. hEvent); if (m_OverlappedWrite. hEvent != NULL) CloseHandle(m_OverlappedWrite. hEvent); CloseHandle(m_hIDComDev); } endd: ; } //發送數據 void CSerialAPIView::OnSend() { char szMessage[20] = “thank you very much”; DWORD dwBytesWritten; for (int i=0; i<sizeof(szMessage); i++) { WriteFile(m_hIDComDev, (LPSTR)&szMessage[i], 1, &dwBytesWritten, &m_OverlappedWrite); if (WaitForSingleObject(m_OverlapperWrite, hEvent, 1000))dwBytesWritten = 0; else{ GentOverlappedResult(m_hIDComDev, &m_OverlappedWrite, &dwBytesWritten, FALSE); m_OverlappedWrite. Offset += dwBytesWritten; } dwBytesWritten++; } }
1.2 接收常式 DCB ComDcb; //設備控制塊 HANDLE hCom; //global handle hCom = CreateFile ("COM1",GENERIC_READ| GENERIC_WRITE,0, NULL,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,NULL); if (hCom==INVALID_HANDLE_VALUE) { AfxMessageBox("無法打開串列口"); } else { COMMTIMEOUTS CommTimeOuts ; SetCommMask(hCom, EV_RXCHAR ) ; SetupComm(hCom, 4096, 4096 ) ; /*設置收發緩衝區 尺寸為4K */ PurgeComm(hCom, PURGE_TXABORT| PURGE_RXABORT | PURGE_TXCLEAR| PURGE_RXCLEAR ) ; //清收發緩衝區 |
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