ModBus協(xié)議

Modbus協(xié)議是一種標(biāo)準(zhǔn)的工業(yè)控制通訊協(xié)議，無論是串口通訊癣漆，以太網(wǎng)通訊還是CAN通訊驾胆，在數(shù)據(jù)層都可以使用Modbus協(xié)議封裝數(shù)據(jù)幀，Modbus協(xié)議支持一對多通信跛锌，采用一問一答的方式保證了通訊數(shù)據(jù)的可靠性和安全性弃秆。

功能碼0x03表示查詢指令，0x06表示寫單個(gè)寄存器指令髓帽，0x10表示寫多個(gè)寄存器指令菠赚。通常情況下，這三個(gè)功能碼就能滿足大多數(shù)實(shí)際場合下的應(yīng)用郑藏。

Modbus協(xié)議單個(gè)收發(fā)指令的字節(jié)數(shù)都是由程序員事先設(shè)計(jì)好的衡查，所以當(dāng)發(fā)送一條指令后，接收指令的字節(jié)長度是確定的必盖，利用這個(gè)規(guī)則筆者設(shè)計(jì)了一個(gè)CSerialPort類來實(shí)現(xiàn)Modbus協(xié)議下的串口編程峡捡。

ModBus協(xié)議詳解

CSerialPort

首先，CSerialPort完成了如下功能筑悴，
1）InitPort()函數(shù)為打開串口们拙，設(shè)定波特率，校驗(yàn)位阁吝，數(shù)據(jù)位砚婆，停止位信息
2）LaunchCommand()函數(shù)完成了指令發(fā)送和接收功能，該函數(shù)在接收代碼部分設(shè)定了代碼保護(hù)區(qū)CRITICAL_SECTION突勇，防止多線程編程時(shí)串口緩沖區(qū)出現(xiàn)異常装盯。

CSerialPort.h如下代碼所示

#ifndef __SERIALPORT_H__
#define __SERIALPORT_H__
 
typedef struct
{
    int type;
    int len;
    char buff[32];
    int timeout;
    int retry;
}LCFLAG;

#define WM_COMM_BREAK_DETECTED      WM_USER+1   // A break was detected on input.
#define WM_COMM_CTS_DETECTED        WM_USER+2   // The CTS (clear-to-send) signal changed state. 
#define WM_COMM_DSR_DETECTED        WM_USER+3   // The DSR (data-set-ready) signal changed state. 
#define WM_COMM_ERR_DETECTED        WM_USER+4   // A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY. 
#define WM_COMM_RING_DETECTED       WM_USER+5   // A ring indicator was detected. 
#define WM_COMM_RLSD_DETECTED       WM_USER+6   // The RLSD (receive-line-signal-detect) signal changed state. 
#define WM_COMM_RXCHAR              WM_USER+7   // A character was received and placed in the input buffer. 
#define WM_COMM_RXFLAG_DETECTED     WM_USER+8   // The event character was received and placed in the input buffer.  
#define WM_COMM_TXEMPTY_DETECTED    WM_USER+9   // The last character in the output buffer was sent.  

class CSerialPort
{                                                        
public:
    // contruction and destruction
    CSerialPort();
    virtual     ~CSerialPort();

    // port initialisation                                          
    BOOL        InitPort(CWnd* pPortOwner, UINT portnr = 1, UINT baud = 57600, char parity = 'N', UINT databits = 8, UINT stopsbits = 1, UINT timeout=80,DWORD dwCommEvents = EV_RXCHAR | EV_CTS, UINT nBufferSize = 512);

    // start/stop comm watching
    BOOL        StartMonitoring();
    BOOL        RestartMonitoring();
    BOOL        StopMonitoring();

    DWORD       GetWriteBufferSize();
    DWORD       GetCommEvents();
    DCB         GetDCB();

    void        WriteToPort(char* string);
    BOOL        OpenPort(CWnd* pPortOwner, UINT portnr = 1, UINT baud = 57600, char parity = 'N', UINT databits = 8, UINT stopsbits = 1, UINT timeout = 80, DWORD dwCommEvents = EV_RXCHAR | EV_CTS, UINT nBufferSize = 512);

protected:
    // protected memberfunctions
    void        ProcessErrorMessage(char* ErrorText);
    static UINT CommThread(LPVOID pParam);
    static void ReceiveChar(CSerialPort* port, COMSTAT comstat);
    static void WriteChar(CSerialPort* port);

    // thread
    CWinThread*         m_Thread;

    // synchronisation objects
    CRITICAL_SECTION    m_csCommunicationSync;
    CRITICAL_SECTION m_csIFSync;

    BOOL                m_bThreadAlive;

    // handles
    HANDLE              m_hShutdownEvent;
    HANDLE              m_hComm;
    HANDLE              m_hWriteEvent;
    HANDLE              m_hRecvEvent;

    // Event array. 
    // One element is used for each event. There are two event handles for each port.
    // A Write event and a receive character event which is located in the overlapped structure (m_ov.hEvent).
    // There is a general shutdown when the port is closed. 
    HANDLE              m_hEventArray[3];

    // structures
    OVERLAPPED          m_ov;
    COMMTIMEOUTS        m_CommTimeouts;
    DCB                 m_dcb;

    // owner window
    CWnd*               m_pOwner;

    // misc
    UINT                m_nPortNr;
    char                m_szWriteBuffer[4096];
    DWORD               m_dwCommEvents;
    DWORD               m_nWriteBufferSize;
public:
    int m_nBufferLen;
    void WriteBin2Port(unsigned char* szBuffer, int nLen);
public:
    void ClosePort(void);
    BOOL ReConfigComPort(int nBaudrate, BYTE nDataBits, int nStopBits, int nParity, int nTimeOut);
    void SetPortOwner(CWnd* pWnd);
    int m_nPort;
    int GetPort(void);
    int LanuchCommand(unsigned char* cmd, int len, unsigned char* recbuff, LCFLAG *pFlag);
    unsigned char m_pRecvBuff[1024];
    int m_RecvLen;
};

#endif __SERIALPORT_H__

CSerialPort.cpp如下代碼所示

/*
**  FILENAME            CSerialPort.cpp
**
**  PURPOSE             This class can read, write and watch one serial port.
**                      It sends messages to its owner when something happends on the port
**                      The class creates a thread for reading and writing so the main
**                      program is not blocked.
*/

#include "stdafx.h"
#include "SerialPort.h"


#include <assert.h>
#include ".\serialport.h"

//
// Constructor
//


CSerialPort::CSerialPort()
: m_nBufferLen(0)
, m_nPort(0)
 , m_RecvLen(0)
{
    m_pOwner = NULL;
    m_hComm = NULL;

    // initialize overlapped structure members to zero
    m_ov.Offset = 0;
    m_ov.OffsetHigh = 0;

    // create events
    m_ov.hEvent = NULL;
    m_hWriteEvent = NULL;
    m_hShutdownEvent = NULL;
    m_hRecvEvent = NULL;

//  m_szWriteBuffer = NULL;

    m_bThreadAlive = FALSE;
}

//
// Delete dynamic memory
//
CSerialPort::~CSerialPort()
{
    do
    {
        SetEvent(m_hShutdownEvent);
    } while (m_bThreadAlive);

    TRACE("Thread ended\n");
    if (m_hComm != NULL)
    {
        CloseHandle(m_hComm);
        m_hComm = NULL;
    }

//  delete [] m_szWriteBuffer;
}

//
// Initialize the port. This can be port 1 to 255.
//
BOOL CSerialPort::InitPort(CWnd* pPortOwner,    // the owner (CWnd) of the port (receives message)
                           UINT  portnr,        // portnumber 
                           UINT  baud,          // baudrate
                           char  parity,        // parity 
                           UINT  databits,      // databits 
                           UINT  stopbits,      // stopbits 
                           UINT  timeout,
                           DWORD dwCommEvents,  // EV_RXCHAR, EV_CTS etc
                           UINT  writebuffersize)   // size to the writebuffer
{
    assert(portnr > 0 && portnr <= 255);
//  assert(pPortOwner != NULL);

    m_nPort=-1;
    // if the thread is alive: Kill
    if (m_bThreadAlive)
    {
        do
        {
            SetEvent(m_hShutdownEvent);
        } while (m_bThreadAlive);
        TRACE("Thread ended\n");
    }

    // create events
    if (m_ov.hEvent != NULL)
        ResetEvent(m_ov.hEvent);
    m_ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

    if (m_hWriteEvent != NULL)
        ResetEvent(m_hWriteEvent);
    m_hWriteEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

    if (m_hRecvEvent != NULL)
        ResetEvent(m_hRecvEvent);
    m_hRecvEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

    if (m_hShutdownEvent != NULL)
        ResetEvent(m_hShutdownEvent);
    m_hShutdownEvent = CreateEvent(NULL, TRUE, FALSE, NULL);


    // initialize the event objects
    m_hEventArray[0] = m_hShutdownEvent;    // highest priority
    m_hEventArray[1] = m_ov.hEvent;
    m_hEventArray[2] = m_hWriteEvent;

    // initialize critical section
    InitializeCriticalSection(&m_csCommunicationSync);
    InitializeCriticalSection(&m_csIFSync);

    // set buffersize for writing and save the owner
    m_pOwner = pPortOwner;

//  if (m_szWriteBuffer != NULL)
//      delete [] m_szWriteBuffer;
    //m_szWriteBuffer = new char[4096];//writebuffersize];
    ////////////////k
//  memset(m_szWriteBuffer,0,sizeof(m_szWriteBuffer));
    //////////////k
    m_nPortNr = portnr;

    m_nWriteBufferSize = 4096;//writebuffersize;
    m_dwCommEvents = dwCommEvents;

    BOOL bResult = FALSE;
    char *szPort = new char[50];
    char *szBaud = new char[50];

    // now it critical!
    EnterCriticalSection(&m_csCommunicationSync);

    // if the port is already opened: close it
    if (m_hComm != NULL)
    {
        CloseHandle(m_hComm);
        m_hComm = NULL;
    }

    // prepare port strings
    sprintf_s(szPort,50, "\\\\.\\COM%d", portnr);
    sprintf_s(szBaud, 50,"baud=%d parity=%c data=%d stop=%d", baud, parity, databits, stopbits);

    // get a handle to the port
    m_hComm = CreateFile(szPort,                        // communication port string (COMX)
                         GENERIC_READ | GENERIC_WRITE,  // read/write types
                         0,                             // comm devices must be opened with exclusive access
                         NULL,                          // no security attributes
                         OPEN_EXISTING,                 // comm devices must use OPEN_EXISTING
                         FILE_FLAG_OVERLAPPED,          // Async I/O
                         0);                            // template must be 0 for comm devices

    if (m_hComm == INVALID_HANDLE_VALUE)
    {
        // port not found
        delete [] szPort;
        delete [] szBaud;
        return FALSE;
    }

    // set the timeout values
    m_CommTimeouts.ReadIntervalTimeout = 
    m_CommTimeouts.ReadTotalTimeoutMultiplier = 
    m_CommTimeouts.ReadTotalTimeoutConstant = 
    m_CommTimeouts.WriteTotalTimeoutMultiplier = 
    m_CommTimeouts.WriteTotalTimeoutConstant = 80;

    // configure
    if (SetCommTimeouts(m_hComm, &m_CommTimeouts))
    {                          
        if (SetCommMask(m_hComm, dwCommEvents))
        {
            if (GetCommState(m_hComm, &m_dcb))
            {
                m_dcb.fRtsControl = RTS_CONTROL_ENABLE;     // set RTS bit high!
                m_dcb.fDtrControl = DTR_CONTROL_ENABLE;     // set RTS bit high!
                if (BuildCommDCB(szBaud, &m_dcb))
                {
                    if (SetCommState(m_hComm, &m_dcb))
                        ; // normal operation... continue
                    else
                        ProcessErrorMessage("SetCommState()");
                }
                else
                    ProcessErrorMessage("BuildCommDCB()");
            }
            else
                ProcessErrorMessage("GetCommState()");
        }
        else
            ProcessErrorMessage("SetCommMask()");
    }
    else
        ProcessErrorMessage("SetCommTimeouts()");

    delete [] szPort;
    delete [] szBaud;

    // flush the port
    PurgeComm(m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);

    // release critical section
    LeaveCriticalSection(&m_csCommunicationSync);

    TRACE("Initialisation for communication port %d completed.\nUse Startmonitor to communicate.\n", portnr);

    m_nPort=portnr;
    return TRUE;
}

//
//  The CommThread Function.
//
UINT CSerialPort::CommThread(LPVOID pParam)
{
    // Cast the void pointer passed to the thread back to
    // a pointer of CSerialPort class
    CSerialPort *port = (CSerialPort*)pParam;
    
    // Set the status variable in the dialog class to
    // TRUE to indicate the thread is running.
    port->m_bThreadAlive = TRUE;    
        
    // Misc. variables
    DWORD BytesTransfered = 0; 
    DWORD Event = 0;
    DWORD CommEvent = 0;
    DWORD dwError = 0;
    COMSTAT comstat;
    BOOL  bResult = TRUE;
        
    // Clear comm buffers at startup
    if (port->m_hComm)      // check if the port is opened
    {
        PurgeComm(port->m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
        ClearCommError(port->m_hComm, &dwError, &comstat);
    }
    // begin forever loop.  This loop will run as long as the thread is alive.
    for (;;) 
    { 

        // Make a call to WaitCommEvent().  This call will return immediatly
        // because our port was created as an async port (FILE_FLAG_OVERLAPPED
        // and an m_OverlappedStructerlapped structure specified).  This call will cause the 
        // m_OverlappedStructerlapped element m_OverlappedStruct.hEvent, which is part of the m_hEventArray to 
        // be placed in a non-signeled state if there are no bytes available to be read,
        // or to a signeled state if there are bytes available.  If this event handle 
        // is set to the non-signeled state, it will be set to signeled when a 
        // character arrives at the port.

        // we do this for each port!

        bResult = WaitCommEvent(port->m_hComm, &Event, &port->m_ov);

        if (!bResult)  
        { 
            // If WaitCommEvent() returns FALSE, process the last error to determin
            // the reason..
            switch (dwError = GetLastError()) 
            { 
            case ERROR_IO_PENDING:  
                { 
                    // This is a normal return value if there are no bytes
                    // to read at the port.
                    // Do nothing and continue
                    break;
                }
            case 87:
                {
                    // Under Windows NT, this value is returned for some reason.
                    // I have not investigated why, but it is also a valid reply
                    // Also do nothing and continue.
                    break;
                }
            default:
                {
                    // All other error codes indicate a serious error has
                    // occured.  Process this error.
                    port->ProcessErrorMessage("WaitCommEvent()");
                    break;
                }
            }
        }
        else
        {
            // If WaitCommEvent() returns TRUE, check to be sure there are
            // actually bytes in the buffer to read.  
            //
            // If you are reading more than one byte at a time from the buffer 
            // (which this program does not do) you will have the situation occur 
            // where the first byte to arrive will cause the WaitForMultipleObjects() 
            // function to stop waiting.  The WaitForMultipleObjects() function 
            // resets the event handle in m_OverlappedStruct.hEvent to the non-signelead state
            // as it returns.  
            //
            // If in the time between the reset of this event and the call to 
            // ReadFile() more bytes arrive, the m_OverlappedStruct.hEvent handle will be set again
            // to the signeled state. When the call to ReadFile() occurs, it will 
            // read all of the bytes from the buffer, and the program will
            // loop back around to WaitCommEvent().
            // 
            // At this point you will be in the situation where m_OverlappedStruct.hEvent is set,
            // but there are no bytes available to read.  If you proceed and call
            // ReadFile(), it will return immediatly due to the async port setup, but
            // GetOverlappedResults() will not return until the next character arrives.
            //
            // It is not desirable for the GetOverlappedResults() function to be in 
            // this state.  The thread shutdown event (event 0) and the WriteFile()
            // event (Event2) will not work if the thread is blocked by GetOverlappedResults().
            //
            // The solution to this is to check the buffer with a call to ClearCommError().
            // This call will reset the event handle, and if there are no bytes to read
            // we can loop back through WaitCommEvent() again, then proceed.
            // If there are really bytes to read, do nothing and proceed.
        
            bResult = ClearCommError(port->m_hComm, &dwError, &comstat);

            if (comstat.cbInQue == 0)
                continue;
        }   // end if bResult

        // Main wait function.  This function will normally block the thread
        // until one of nine events occur that require action.
        Event = WaitForMultipleObjects(3, port->m_hEventArray, FALSE, INFINITE);

        switch (Event)
        {
        case 0:
            {
                // Shutdown event.  This is event zero so it will be
                // the higest priority and be serviced first.

                port->m_bThreadAlive = FALSE;
                
                // Kill this thread.  break is not needed, but makes me feel better.
                AfxEndThread(100);
                break;
            }
        case 1: // read event
            {
                GetCommMask(port->m_hComm, &CommEvent);
                //if (CommEvent & EV_CTS)
                //  ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_CTS_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
                //if (CommEvent & EV_RXFLAG)
                //  ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_RXFLAG_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
                //if (CommEvent & EV_BREAK)
                //  ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_BREAK_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
                //if (CommEvent & EV_ERR)
                //  ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_ERR_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
                //if (CommEvent & EV_RING)
                //  ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_RING_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
                
                if (CommEvent & EV_RXCHAR)
                    // Receive character event from port.
                    ReceiveChar(port, comstat);
                    
                break;
            }  
        case 2: // write event
            {
                // Write character event from port
                WriteChar(port);
                break;
            }

        } // end switch

    } // close forever loop

    return 0;
}

//
// start comm watching
//
BOOL CSerialPort::StartMonitoring()
{
    if (!(m_Thread = AfxBeginThread((AFX_THREADPROC)CommThread, this,THREAD_PRIORITY_HIGHEST)))
        return FALSE;
    TRACE("Thread started\n");
    return TRUE;    
}

//
// Restart the comm thread
//
BOOL CSerialPort::RestartMonitoring()
{
    TRACE("Thread resumed\n");
    m_Thread->ResumeThread();
    return TRUE;    
}


//
// Suspend the comm thread
//
BOOL CSerialPort::StopMonitoring()
{
    TRACE("Thread suspended\n");
    m_Thread->SuspendThread(); 
    return TRUE;    
}


//
// If there is a error, give the right message
//
void CSerialPort::ProcessErrorMessage(char* ErrorText)
{
    char *Temp = new char[200];
    
    LPVOID lpMsgBuf;

    FormatMessage( 
        FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
        NULL,
        GetLastError(),
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
        (LPTSTR) &lpMsgBuf,
        0,
        NULL 
    );

    sprintf_s(Temp,200, "WARNING:  %s Failed with the following error: \n%s\nPort: %d\n", (char*)ErrorText, lpMsgBuf, m_nPortNr); 
    MessageBox(NULL, Temp, "Application Error", MB_ICONSTOP);

    LocalFree(lpMsgBuf);
    delete[] Temp;
}

//
// Write a character.
//
void CSerialPort::WriteChar(CSerialPort* port)
{
    BOOL bWrite = TRUE;
    BOOL bResult = TRUE;

    DWORD BytesSent = 0;

    ResetEvent(port->m_hWriteEvent);

    // Gain ownership of the critical section
    EnterCriticalSection(&port->m_csCommunicationSync);

    if (bWrite)
    {
        // Initailize variables
        port->m_ov.Offset = 0;
        port->m_ov.OffsetHigh = 0;

        // Clear buffer
//      PurgeComm(port->m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);

        bResult = WriteFile(port->m_hComm,                          // Handle to COMM Port
                            port->m_szWriteBuffer,                  // Pointer to message buffer in calling finction
                            port->m_nWriteBufferSize,
                            //                          strlen((char*)port->m_szWriteBuffer),   // Length of message to send
                            &BytesSent,                             // Where to store the number of bytes sent
                            &port->m_ov);                           // Overlapped structure

        // deal with any error codes
        if (!bResult)  
        {
            DWORD dwError = GetLastError();
            switch (dwError)
            {
                case ERROR_IO_PENDING:
                    {
                        // continue to GetOverlappedResults()
                        BytesSent = 0;
                        bWrite = FALSE;
                        break;
                    }
                default:
                    {
                        // all other error codes
                        port->ProcessErrorMessage("WriteFile()");
                    }
            }
        } 
        else
        {
            LeaveCriticalSection(&port->m_csCommunicationSync);
        }
    } // end if(bWrite)

    if (!bWrite)
    {
        bWrite = TRUE;
    
        bResult = GetOverlappedResult(port->m_hComm,    // Handle to COMM port 
                                      &port->m_ov,      // Overlapped structure
                                      &BytesSent,       // Stores number of bytes sent
                                      TRUE);            // Wait flag

        LeaveCriticalSection(&port->m_csCommunicationSync);

        // deal with the error code 
        if (!bResult)  
        {
            port->ProcessErrorMessage("GetOverlappedResults() in WriteFile()");
        }   
    } // end if (!bWrite)

    // Verify that the data size send equals what we tried to send
    if (BytesSent != port->m_nWriteBufferSize)//strlen((char*)port->m_szWriteBuffer))
    {
//      CString str;
//      str.Format("WARNING: WriteFile() error.. Bytes Sent: %d; Message Length: %d\n", BytesSent, strlen((char*)port->m_szWriteBuffer));
//  AfxMessageBox(str);
    }
//  memset(port->m_szWriteBuffer,0,strlen((char*)port->m_szWriteBuffer));

//  ::PostMessage((port->m_pOwner)->m_hWnd, WM_COMM_RXCHAR, (WPARAM) 1, (LPARAM) 0);

}

//
// Character received. Inform the owner
//
void CSerialPort::ReceiveChar(CSerialPort* port, COMSTAT comstat)
{
    BOOL  bRead = TRUE; 
    BOOL  bResult = TRUE;
    DWORD dwError = 0;
    DWORD BytesRead = 0;
    unsigned char RXBuff;

    for (;;) 
    { 
        // Gain ownership of the comm port critical section.
        // This process guarantees no other part of this program 
        // is using the port object. 
        
        EnterCriticalSection(&port->m_csCommunicationSync);

        // ClearCommError() will update the COMSTAT structure and
        // clear any other errors.
        
        bResult = ClearCommError(port->m_hComm, &dwError, &comstat);

        LeaveCriticalSection(&port->m_csCommunicationSync);

        // start forever loop.  I use this type of loop because I
        // do not know at runtime how many loops this will have to
        // run. My solution is to start a forever loop and to
        // break out of it when I have processed all of the
        // data available.  Be careful with this approach and
        // be sure your loop will exit.
        // My reasons for this are not as clear in this sample 
        // as it is in my production code, but I have found this 
        // solutiion to be the most efficient way to do this.
        
        if (comstat.cbInQue == 0)
        {
            // break out when all bytes have been read
            break;
        }
                        
        EnterCriticalSection(&port->m_csCommunicationSync);

        if (bRead)
        {
            bResult = ReadFile(port->m_hComm,       // Handle to COMM port 
                               &RXBuff,             // RX Buffer Pointer
                               1,                   // Read one byte
                               &BytesRead,          // Stores number of bytes read
                               &port->m_ov);        // pointer to the m_ov structure
            // deal with the error code 
            if (!bResult)  
            { 
                switch (dwError = GetLastError()) 
                { 
                    case ERROR_IO_PENDING:  
                        { 
                            // asynchronous i/o is still in progress 
                            // Proceed on to GetOverlappedResults();
                            bRead = FALSE;
                            break;
                        }
                    default:
                        {
                            // Another error has occured.  Process this error.
                            port->ProcessErrorMessage("ReadFile()");
                            break;
                        } 
                }
            }
            else
            {
                // ReadFile() returned complete. It is not necessary to call GetOverlappedResults()
                bRead = TRUE;
            }
        }  // close if (bRead)

        if (!bRead)
        {
            bRead = TRUE;
            bResult = GetOverlappedResult(port->m_hComm,    // Handle to COMM port 
                                          &port->m_ov,      // Overlapped structure
                                          &BytesRead,       // Stores number of bytes read
                                          TRUE);            // Wait flag

            // deal with the error code 
            if (!bResult)  
            {
                port->ProcessErrorMessage("GetOverlappedResults() in ReadFile()");
            }   
        }  // close if (!bRead)
        
        if (port->m_RecvLen<1024)
        {
            port->m_pRecvBuff[port->m_RecvLen++] = RXBuff;
            //int len=port->
            //port->m_pRecvBuff[(*(port->m_pRecvLen))++] = RXBuff;
            SetEvent(port->m_hRecvEvent);
        }

        LeaveCriticalSection(&port->m_csCommunicationSync);

        // notify parent that a byte was received
        if(port->m_pOwner)
            ::PostMessage((port->m_pOwner)->m_hWnd, WM_COMM_RXCHAR, (WPARAM)RXBuff, (LPARAM)port->m_nPortNr);
    } // end forever loop

}

//
// Write a string to the port
//
void CSerialPort::WriteToPort(char* string)
{       
    assert(m_hComm != 0);

//  memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));
    strcpy_s(m_szWriteBuffer,4096, string);
//  strcat(m_szWriteBuffer, string);
    m_nWriteBufferSize=(DWORD)strlen(string);
    // set event for write
    SetEvent(m_hWriteEvent);
}

//
// Return the device control block
//
DCB CSerialPort::GetDCB()
{
    return m_dcb;
}

//
// Return the communication event masks
//
DWORD CSerialPort::GetCommEvents()
{
    return m_dwCommEvents;
}

//
// Return the output buffer size
//
DWORD CSerialPort::GetWriteBufferSize()
{
    return m_nWriteBufferSize;
}





void CSerialPort::WriteBin2Port(unsigned char* szBuffer, int nLen)
{
    memcpy(m_szWriteBuffer,szBuffer,nLen);
    m_nWriteBufferSize=nLen;
    SetEvent(m_hWriteEvent);
}

void CSerialPort::ClosePort(void)
{

    do
    {
        SetEvent(m_hShutdownEvent);
    } while (m_bThreadAlive);

    TRACE("Thread ended\n");
    if (m_hComm != NULL)
    {
        CloseHandle(m_hComm);
        m_hComm = NULL;
    }

}
//
//BOOL CSerialPort::ReConfigComPort(int nBaudrate, BYTE nDataBits, int nStopBits, int nParity, int nTimeOut)
//{
////    COMMTIMEOUTS        commTimeouts;
////    commTimeouts.ReadIntervalTimeout=
////    commTimeouts.ReadTotalTimeoutConstant=
////    commTimeouts.ReadTotalTimeoutMultiplier=
////    commTimeouts.WriteTotalTimeoutConstant=
////    commTimeouts.WriteTotalTimeoutMultiplier=nTimeOut;
////
////    /*  switch(nBaudrate)
////    {
////    case 0:
////        m_dcb.BaudRate=CBR_1200;
////        break;
////    case 1:
////        m_dcb.BaudRate=CBR_2400;
////        break;
////    case 2:
////        m_dcb.BaudRate=CBR_4800;
////        break;
////    case 3:
////        m_dcb.BaudRate=CBR_9600;
////        break;
////    case 3:
////        m_dcb.BaudRate=CBR_9600;
////        break;
////    m_dcb.BaudRate
////*/
////    m_dcb.BaudRate=BAUDRATES[nBaudrate];
////    m_dcb.ByteSize=nDataBits;
/////*  m_dcb.Parity=NOPARITY;
////    m_dcb.Parity=ODDPARITY;
////    m_dcb.Parity=EVENPARITY;
////*/
////    m_dcb.Parity=PARITY[nParity];
/////*  m_dcb.StopBits=ONESTOPBIT;
////    m_dcb.StopBits=ONE5STOPBITS;
////    m_dcb.StopBits=TWOSTOPBITS;
////*/
////    m_dcb.StopBits=STOPBITS[nStopBits];
////
////    return  SetCommTimeouts(m_hComm, &commTimeouts)&&SetCommState(m_hComm,&m_dcb);
////
//  return 0;
//}
//
void CSerialPort::SetPortOwner(CWnd* pWnd)
{
    m_pOwner=pWnd;
}

int CSerialPort::GetPort(void)
{
    return m_nPort;
}

BOOL CSerialPort::OpenPort(CWnd* pPortOwner, 
    UINT  portnr, 
    UINT  baud,  
    char  parity, 
    UINT  databits,  
    UINT  stopbits,   
    UINT  timeout,
    DWORD dwCommEvents, UINT  writebuffersize)  // size to the writebuffer
{
    if (m_hComm)
    {
        ClosePort();
        Sleep(1000);

    }
    if (InitPort(pPortOwner, portnr, baud, parity, databits, stopbits, timeout, dwCommEvents, writebuffersize))
    {
        StartMonitoring();
        return TRUE;
    }
    else return FALSE;
}

int CSerialPort::LanuchCommand(unsigned char* cmd, int len, unsigned char* pRecBuff, LCFLAG *pFlag)
{
    int recvlen = 0;

    if (m_hComm&&m_hComm != INVALID_HANDLE_VALUE)
    {
        EnterCriticalSection(&m_csIFSync);

        BOOL bSucc = FALSE;
        int retry = pFlag->retry;

        do
        {
            EnterCriticalSection(&m_csCommunicationSync);

            //  m_pRecvBuff = pRecBuff;
            m_RecvLen = 0;// &recvlen;
            LeaveCriticalSection(&m_csCommunicationSync);
            ResetEvent(m_hRecvEvent);
            WriteBin2Port(cmd, len);


            while (1)
            {
                if (retry) retry--;
                if (WAIT_OBJECT_0 == WaitForSingleObject(m_hRecvEvent, pFlag->timeout))
                {
                    EnterCriticalSection(&m_csCommunicationSync);
                    // 如果返回值長度等于設(shè)定的字節(jié)長度
                    if (m_RecvLen >= pFlag->len)
                    {
                        memcpy(pRecBuff, m_pRecvBuff, recvlen = m_RecvLen);
                        bSucc = TRUE;
                    }

                    LeaveCriticalSection(&m_csCommunicationSync);
                    ResetEvent(m_hRecvEvent);
                    if (bSucc)
                    {
                        retry = 0;
                        break;
                    }
                }
                else break;
            }

        } while (!bSucc && retry);
        LeaveCriticalSection(&m_csIFSync);
    }
    return recvlen;

}

使用方法

使用InitPort初始化串口，返回值為BOOL類型甲馋，TRUE表示初始化正常埂奈，串口打開成功，否則失敗定躏。

    CSerialEx* pEx = (CSerialEx*)pParam;
// 初始化串口
    if (pEx->m_Port.InitPort(NULL, pEx->m_serial.cfg.port,
        BAUDRATES[pEx->m_serial.cfg.baudrate],
        PARITY[pEx->m_serial.cfg.parity],
        DATABITS[pEx->m_serial.cfg.databits],
        STOPBITS[pEx->m_serial.cfg.stopbits]
        )
        )
    {
        pEx->m_Port.StartMonitoring(); //開啟串口接收線程
        pEx->m_bConnect = TRUE;
        while (1)
        {
            Sleep(50);
            Poll(pEx);
        }
    }

使用LaunchCommand函數(shù)實(shí)現(xiàn)發(fā)送與接收账磺，返回值為接收數(shù)據(jù)字節(jié)長度

BYTE buff[8]; // 發(fā)送指令數(shù)組
BYTE recvBuff[1024]; // 接收指令數(shù)組
LCFLAG flag; // 結(jié)構(gòu)體
int recvlen; // 接收字節(jié)長度
WORD wCrc; // crc校驗(yàn)位

int i = 0;
buff[i++] = pDevEx->Dev.addr;  // 從站地址
buff[i++] = 0x03;
buff[i++] = 0x00;
buff[i++] = 0x09;
buff[i++] = 0x00;
buff[i++] = 0x01;
wCrc = GetCrcCode((const char*)buff, i); // 獲取CRC校驗(yàn)
buff[i++] = LOBYTE(wCrc); // CRC低字節(jié)
buff[i++] = HIBYTE(wCrc); // CRC高字節(jié)

memset(&flag, 0, sizeof(LCFLAG));
memset(recvBuff, 0, 1024);
flag.len = 0x07; // 設(shè)定接收字節(jié)長度
flag.timeout = pEx->m_serial.cfg.timeout; // 設(shè)定接收超時(shí)時(shí)間，單位ms
flag.retry = 0x03;  // 設(shè)定重發(fā)次數(shù)
recvlen = pEx->m_Port.LanuchCommand(buff, sizeof(buff), recvBuff, &flag); // 發(fā)送數(shù)據(jù)痊远，返回值為接收數(shù)據(jù)的字節(jié)長度

// recvlen如果等于設(shè)定的接收字節(jié)長度且返回值的第一個(gè)字節(jié)等于從站地址垮抗，就認(rèn)為接收發(fā)送正確
if (recvlen == 0x07 && recvBuff[0] == pDevEx->Dev.addr)
{
    // 填寫接收數(shù)據(jù)解析代碼
    // recvBuff為接收數(shù)據(jù)數(shù)組
}

其中GetCrcCode()代碼如下所示

WORD GetCrcCode(const char* ptr, int len)
{
    WORD wCrc = WORD(0xFFFF);
    for (int i = 0; i<len; i++)
    {
        WORD wd = WORD(BYTE(ptr[i]));
        wCrc ^= wd; // 異或運(yùn)算符
        for (int j = 0; j<8; j++)
        {
            if (wCrc & 1)
            {
                wCrc >>= 1; // 右移一位
                wCrc ^= 0xA001;
            }
            else{
                wCrc >>= 1;
            }
        }
    }
    return wCrc;
}

結(jié)論

1）Modbus協(xié)議的在發(fā)送指令確定的前提下，接收數(shù)據(jù)的長度是可以確定的碧聪，等于0x05+讀寫寄存器個(gè)數(shù)*2冒版，所以可以利用這一點(diǎn)來確定串口接收字節(jié)的長度，在SerialPort.cpp的LaunchCommand函數(shù)中可以看到if (m_RecvLen >= pFlag->len)這樣一條判斷語句逞姿。
2）LCFLAG結(jié)構(gòu)體定義了發(fā)送和接收指令的一個(gè)附加屬性結(jié)構(gòu)體辞嗡，其中type表示協(xié)議捆等，len表示接收數(shù)據(jù)長度，buff[32]保留功能续室，timeout表示接收超時(shí)時(shí)間楚里，retry表示重發(fā)次數(shù)。在發(fā)送指令之前猎贴，必須初始化該結(jié)構(gòu)體，如果是Modbus協(xié)議蝴光，必須給結(jié)構(gòu)體的len賦值她渴，且該值必須等于接收數(shù)據(jù)的字節(jié)長度。
3）讀者可以嘗試自己改寫LaunchCommand函數(shù)蔑祟，實(shí)現(xiàn)諸如標(biāo)準(zhǔn)的SCPI協(xié)議或者各類自定義協(xié)議的串口編程趁耗，只要給LCFLAG的type指定一種協(xié)議，在LauncCommand函數(shù)中去根據(jù)type指定的協(xié)議添加適合的代碼去完成數(shù)據(jù)的接收疆虚。