在VB中利用API进行串口通信
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。
同时，由于串口通信是基于字节流的，为方便程序设计，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。
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
