Private Function OpenThePort(cPort as String,cBaud as String,cParity
as String,cData as String,tStops asString)As Boolean ’ 打开串口的子过程
Dim lResult as Long
Dim lHandle as Long
Dim DCB_COMM as DCB
Dim cDCBConfig as String
lHandle = CreateFile(cPort,GENERIC_READ Or GENERIC_WRITE,
0&,0&,OPEN_EXISTING,0&,0&)
If lHandle = -1 Then ’打开串口失败
OpenThePort = False
MsgBox “串口可能正被其他应用程序占用!”
lResult = CloseHandle(lHandle) ’先关闭串口后再打开
If lResult = 0 Then
OpenThePort
Exit Function
End If
End If
cDCBConfig.band = 2400 ’设置DCB
cDCBConfig.parity = None
cDCBConfig.data = 8
cDCBConfig.stop = 1
lResult = BuildCommDCB(cDCBConfig,DCB_COMM) ’按用户设定配置一个DCB结构
If lResult = 0 Then
OpenThePort = False
MsgBox “无法建立DCB设备控制块”
Exit Function
End If
lResult = SetCommState(lHandle,DCB_Comm) ’实际设置一个串口的DCB
If lResult = 0 Then
OpenThePort = False
MsgBox “无法建立DCB设备控制块”
Exit Function
End If
OpenThePort = True
End Function
Private Sub SendHand ( ) ’发送握手信号的子过程
Dim Nchars As Long
Static Readbuff As String * 1
Static Writebuff As String * 1
Dim lpDCB As DCB
Dim lRet As Long
Dim lHandle As Long
Dim lpOverlapped As OVERLAPPED
Dim RNum As Integer
MsgBox “请把读卡器插在串口2上!”,
48,“提示窗口”
lHandle = OpenThePort(COMM1,2400,None,8,1)
lRet = PurgeComm( lHandle,1 ) ’清输出缓冲区
lRet = PurgeComm( lHandle,0 ) ’清输入缓冲区
lRet = GetCommState ( lHandle,lpDCB ) ’获得通讯口的状态
Shand:
Writebuff$= Chr$(&H8F)
lRet = WriteFile (lHandle,Writebuff$,1,Nchars,lpOverlapped )
’送握手信号入串口缓冲区
If lRet <= 0 Then
MsgBox “发送操作出错,卡握手信号未发送成功”, 16
GoTo Shand ’不成功则重发
Else
GoTo Qtest
End If
GoTo Shand
Qtest:
Readbuff$ =“ ” ’清除缓冲区为空
Do While lHandle ’循环查询串口
RNum = 0 ’设置读串口次数的指针为0
ReadAgain:
lRet = ReadFile( lHandle, Readbuff$,1,Nchars,lpOverlapped )
If lRet < 0 Then
MsgBox “读取应答信号时出错”, 16
End If
If lRet = 0 Then
If RNum > 1000 Then ’只读1000次串口,以免陷入死循环
MsgBox
"卡没有插接好或卡没有接在串口上!"
GoTo CloseP
End If
RNum = RNum + 1
GoTo ReadAgain
End If
If Hex$(Asc(Readbuff)) <> Hex$(&HFF) Then GoTo Shand
’回送码不正确则返回继续发送握手信号
Else
Label1.Caption = “握手信号是:”
+Hex$(Asc(Readbuff$))
Msgbox “握手信号正确,已正确联机”
GoTo CloseP
End If
Loop
CloseP:lRet = CloseHandle( lHandle )
If lRet = 0 Then
MsgBox “串行通讯口关闭成功”,
48,“提示窗口”
End If
End Sub
这里要注意的是:当PC机与单片机系统通信时,单片机数据存储区( RAM )内的数据是十六进制,在信号线上传输的是十六进制数的ASCII码的二进制形式;而Windows系统下使用的是ANSI码,ANSI码仅在前126个与ASCII码相同。即在Win95下接收到的是十六进制数的ASCII码的字符串,可先转换为ANSI码后再在Win95下还原为十六进制数。 具体为:Code$=Hex$(Asc ( Readbuff$ ) ) 另外,由于32位API函数参数的数据类型的变化,所有整形参数都被换为长整型(Long)以支持32位的处理,这一点在设置返回值时尤其如此。
6 结束语
以上的软硬件在我们的实践中达到了较为理想的效果。通过软件节省了硬件的开销,并通过在PIC16F84单片机系统和PC机双方的通信软件内增加握手信号,达到了软件数据校验的目的,获得了较高的通信可靠性。
参 考 文 献
1 MICROCHIP CO. PIC16/17 MICROCO-NTROLLER DATA BOOK. 1995/1996 2 李东星等. PIC16CXX系列单片机应用设计. 高奇电子科技公司,1996.10 3 美 Darwin Boyle等. Visual Basic 4 Developer’s Guide. 北京:机械工业出版社,1997. |