在VB中利用API进行串口通信

    一般来说，在VB中编写串口通讯程序，首先考虑到是使用MSComm控件，可是该控件不能设置超时，而且对许多内部的参数进行了隐藏，从而不能满足有些具体的工作。而使用API进行串口通信，大多是使用VC，很少见到完整的VB代码，为此，我编写了这个模块。

    同时，由于串口通信是基于字节流的，为方便程序设计，我还编写了三个简单的辅助函数，并写了一个详细的测试代码。

    如果读者有好的建议，欢迎留言告知。具体代码如下：

 '* ******************************************************* * '* 程序名称：basComm.bas '* 程序功能：在VB中利用API进行串口通信 '* 作者：lyserver '* 联系方式：http://blog.csdn.net/lyserver '* ******************************************************* * Option Explicit Option Base 0 Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, ByVal lpSecurityAttributes As Long, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long Private Declare Function ReadFile Lib "kernel32" (ByVal hFile As Long, lpBuffer As Any, ByVal nNumberOfBytesToRead As Long, lpNumberOfBytesRead As Long, ByVal lpOverlapped As Long) As Long Private Declare Function WriteFile Lib "kernel32" (ByVal hFile As Long, lpBuffer As Any, ByVal nNumberOfBytesToWrite As Long, lpNumberOfBytesWritten As Long, ByVal lpOverlapped As Long) As Long Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long Private Const GENERIC_READ = &H80000000 Private Const GENERIC_WRITE = &H40000000 Private Const OPEN_EXISTING = 3 Private Const INVALID_HANDLE_VALUE = -1 Private Declare Function GetCommState Lib "kernel32" (ByVal nCid As Long, lpDCB As DCB) As Long Private Declare Function SetCommState Lib "kernel32" (ByVal hCommDev As Long, lpDCB As DCB) As Long Private Declare Function SetCommTimeouts Lib "kernel32" (ByVal hFile As Long, lpCommTimeouts As COMMTIMEOUTS) As Long Private Declare Function SetupComm Lib "kernel32" (ByVal hFile As Long, ByVal dwInQueue As Long, ByVal dwOutQueue As Long) As Long Private Declare Function PurgeComm Lib "kernel32" (ByVal hFile As Long, ByVal dwFlags As Long) As Long Private Const PURGE_TXABORT = &H1 ' Kill the pending/current writes to the comm port. Private Const PURGE_RXABORT = &H2 ' Kill the pending/current reads to the comm port. Private Const PURGE_TXCLEAR = &H4 ' Kill the transmit queue if there. Private Const PURGE_RXCLEAR = &H8 ' Kill the typeahead buffer if there. Private Type DCB DCBlength As Long BaudRate As Long fBitFields As Long 'See Comments in Win32API.Txt wReserved As Integer XonLim As Integer XoffLim As Integer ByteSize As Byte Parity As Byte StopBits As Byte XonChar As Byte XoffChar As Byte ErrorChar As Byte EOFChar As Byte EvtChar As Byte wReserved1 As Integer 'Reserved; Do Not Use End Type Private Type COMMTIMEOUTS ReadIntervalTimeout As Long ReadTotalTimeoutMultiplier As Long ReadTotalTimeoutConstant As Long WriteTotalTimeoutMultiplier As Long WriteTotalTimeoutConstant As Long End Type Private Declare Function SafeArrayGetDim Lib "oleaut32.dll" (ByRef saArray() As Any) As Long '串口操作演示 Sub Main() Dim hComm As Long Dim szTest As String '打开串口1 hComm = OpenComm(1) If hComm <> 0 Then '设置串口通讯参数 SetCommParam hComm '设置串口超时 SetCommTimeOut hComm, 2, 3 '向串口写入字符串123 szTest = "123" WriteComm hComm, StringToBytes(szTest) '读串口 szTest = BytesToString(ReadComm(hComm)) Debug.Print szTest '关闭串口 CloseComm hComm End If End Sub '打开串口 Function OpenComm(ByVal lComPort As Long) As Long Dim hComm As Long hComm = CreateFile("COM" & lComPort, GENERIC_READ Or GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0) If hComm = INVALID_HANDLE_VALUE Then OpenComm = 0 Else OpenComm = hComm End If End Function '关闭串口 Sub CloseComm(hComm As Long) CloseHandle hComm hComm = 0 End Sub '读串口 Function ReadComm(ByVal hComm As Long) As Byte() Dim dwBytesRead As Long Dim BytesBuffer() As Byte ReDim BytesBuffer(4095) ReadFile hComm, BytesBuffer(0), UBound(BytesBuffer) + 1, dwBytesRead, 0 If dwBytesRead > 0 Then ReDim Preserve BytesBuffer(dwBytesRead) ReadComm = BytesBuffer End If End Function '写串口 Function WriteComm(ByVal hComm As Long, BytesBuffer() As Byte) As Long Dim dwBytesWrite If SafeArrayGetDim(BytesBuffer) = 0 Then Exit Function WriteFile hComm, BytesBuffer(0), UBound(BytesBuffer) + 1, dwBytesWrite, 0 WriteComm = dwBytesWrite End Function '设置串口通讯参数 Function SetCommParam(ByVal hComm As Long, Optional ByVal lBaudRate As Long = 9600, _ Optional ByVal cByteSize As Byte = 8, Optional ByVal cStopBits As Byte = 0, _ Optional ByVal cParity As Byte = 0, Optional ByVal cEOFChar As Long = 26) As Boolean Dim dc As DCB If hComm = 0 Then Exit Function If GetCommState(hComm, dc) Then dc.BaudRate = lBaudRate dc.ByteSize = cByteSize dc.StopBits = cStopBits dc.Parity = cParity dc.EOFChar = cEOFChar SetCommParam = CBool(SetCommState(hComm, dc)) End If End Function '设置串口超时 Function SetCommTimeOut(ByVal hComm As Long, Optional ByVal dwReadTimeOut As Long = 2, _ Optional ByVal dwWriteTimeOut As Long = 3) As Boolean Dim ct As COMMTIMEOUTS If hComm = 0 Then Exit Function ct.ReadIntervalTimeout = dwReadTimeOut '读操作时，字符间超时 ct.ReadTotalTimeoutMultiplier = dwReadTimeOut '读操作时，每字节超时 ct.ReadTotalTimeoutConstant = dwReadTimeOut '读操作时，固定超时（总超时=每字节超时*字节数+固定超时） ct.WriteTotalTimeoutMultiplier = dwWriteTimeOut '写操作时，每字节超时 ct.WriteTotalTimeoutConstant = dwWriteTimeOut '写操作时，固定超时（总超时=每字节超时*字节数+固定超时） SetCommTimeOut = CBool(SetCommTimeouts(hComm, ct)) End Function '设置串口读写缓冲区大小 Function SetCommBuffer(ByVal hComm As Long, Optional ByVal dwBytesRead As Long = 1024, _ Optional ByVal dwBytesWrite As Long = 512) As Boolean If hComm = 0 Then Exit Function SetCommBuffer = CBool(SetupComm(hComm, dwBytesRead, dwBytesWrite)) End Function '清空串口缓冲区 Sub ClearComm(ByVal hComm As Long, Optional ByVal InBuffer As Boolean = True, Optional ByVal OutBuffer As Boolean = True) If hComm = 0 Then Exit Sub If InBuffer And OutBuffer Then '清空输入输出缓冲区 PurgeComm hComm, PURGE_TXABORT Or PURGE_RXABORT Or PURGE_TXCLEAR Or PURGE_RXCLEAR ElseIf InBuffer Then '清空输入缓冲区 PurgeComm hComm, PURGE_RXABORT Or PURGE_RXCLEAR ElseIf OutBuffer Then '清空输出缓冲区 PurgeComm hComm, PURGE_TXABORT Or PURGE_TXCLEAR End If End Sub '辅助函数：BSTR字符串转换为CHAR字符串 Function StringToBytes(ByVal szText As String) As Byte() If Len(szText) > 0 Then StringToBytes = StrConv(szText, vbFromUnicode) End If End Function '辅助函数：CHAR字符串转换为BSTR字符串 Function BytesToString(bytesText() As Byte) As String If SafeArrayGetDim(bytesText) <> 0 Then BytesToString = StrConv(bytesText, vbUnicode) End If End Function '辅助函数：获得CHAR字符串长度 Function Byteslen(bytesText() As Byte) As Long If SafeArrayGetDim(bytesText) <> 0 Then Byteslen = UBound(bytesText) + 1 End If End Function