AB系列的PLC一般都有专用的驱动程序用于实现PLC和计算机之间的通讯，如RSLINX就是专门用于做这项工作的，但使用RSLINX也具有一定的局限性，这里提供一个使用VB编程实现PLC和计算机之间的通讯程序，使用的协议是DF1，可以支持Micrologix、SLC500等系列的PLC。使用的代码如下：
Option Explicit
Dim tns%, comunicating
Private Sub Command1_Click()
ReDim tb%(10)
Dim st
If ReadTable(0, tb%()) Then
For st = 0 To 9 '显示结果
字串2
Text1.SelText = Str(tb%(st)) + Chr(32)
Next st
Text1.SelText = Chr(13) + Chr(10)
End If
End Sub
Private Sub Command2_Click()
ReDim tm%(5)
tm%(0) = Rnd * 32768
tm%(1) = Rnd * 32768
tm%(2) = Rnd * 32768
tm%(3) = Rnd * 32768
tm%(4) = Rnd * 32768
If Not WriteTable(4, tm%()) Then Text1.SelText = "写入错误！！"
End Sub
Private Sub Exit_Click()
Unload Me
End
End Sub
Private Sub Form_Load()
字串9
Comm1.PortOpen = True
End Sub
Private Sub Form_Unload(Cancel As Integer)
Comm1.PortOpen = False
End Sub
Private Sub CalcCRC(mes$)
Dim byt%, res&
'对消息进行crc校验，然后将结果添加到消息的结尾。
byt% = 3
Do
res& = res& Xor Asc(Mid(mes$, byt%, 1))
rotate res&
If Asc(Mid(mes$, byt%, 1)) = 16 Then
mes$ = Left$(mes$, byt%) + Chr(16) + Right$(mes$, Len(mes$) - byt%)
byt% = byt% + 1
End If
byt% = byt% + 1 字串4
Loop While (byt% <= Len(mes$) - 2)
res& = res& Xor 3
rotate res&
mes$ = mes$ + Chr(res& Mod 256) + Chr(Int(res& / 256))
End Sub
Function ReadTable(start, n%())
Dim st, com$
'从PLC CIF数据表中读取数据, Micrologix=N7 SLC500=N9
If comunicating Then Exit Function
comunicating = True
Form1.Comm1.InputLen = 0 '清缓冲区
com$ = Form1.Comm1.Input
'构建消息
com$ = Chr(16) + Chr(2) + Chr(0) + Chr(0)
com$ = com$ + Chr(1) + Chr(0) + Chr(tns%) + Chr(0)
字串8
com$ = com$ + Chr(start) + Chr(0) + Chr(UBound(n%) * 2)
com$ = com$ + Chr(16) + Chr(3)
'进行crc计算并附加到结尾。
CalcCRC com$
tns% = tns% + 1
If tns% = 256 Then tns% = 0
'发送命令
Form1.Comm1.Output = com$
'等待确认
st = Timer
Do
DoEvents
Loop While st + 3 > Timer And Form1.Comm1.InBufferCount < 2
'从缓冲中移除确认
Form1.Comm1.InputLen = 2
com$ = Form1.Comm1.Input
If com$ <> Chr(16) + Chr(6) Then 字串7
comunicating = False
Exit Function
End If
st = Timer '等待应答
Do
DoEvents
Loop While st + 3 > Timer And Form1.Comm1.InBufferCount < 12 + (UBound(n%)
* 2)
'超时则退出
If Form1.Comm1.InBufferCount < 12 + (UBound(n%) * 2) Then
comunicating = False
Exit Function
End If
'发送确认
Form1.Comm1.Output = Chr(16) + Chr(6)
'得到应答
Form1.Comm1.InputLen = 0
com$ = Form1.Comm1.Input 字串6
st = 3
Do
If Mid(com$, st, 1) = Chr(16) Then
com$ = Left(com$, st) + Right(com$, Len(com$) - 1 - st)
End If
st = st + 1
Loop While st < Len(com$) - 4
'保存结果
For st = 0 To UBound(n%) - 1
n%(st) = 256 * Asc(Mid(com$, 2 * st + 10, 1)) + Asc(Mid(com$, 2 * st + 9,
1))
Next st
ReadTable = True
comunicating = False
End Function
Private Sub rotate(res&)
Dim bitout%, shift%
For shift% = 1 To 8 字串9
bitout% = res& Mod 2
res& = Int(res& / 2)
If bitout% Then
res& = res& Xor &H1000A001
res& = res& - &H10000000
End If
Next shift%
End Sub
Function WriteTable(start, n%())
Dim st, com$
'写到 PLC CIF数据表, Micrologix=N7 SLC500=N9
If comunicating Then Exit Function
comunicating = True
Form1.Comm1.InputLen = 0
com$ = Form1.Comm1.Input
com$ = Chr(16) + Chr(2) + Chr(0) + Chr(0) 字串6
com$ = com$ + Chr(8) + Chr(0) + Chr(tns%) + Chr(0)
com$ = com$ + Chr(start) + Chr(0)
For st = 0 To UBound(n%)
com$ = com$ + Chr(n%(st) Mod 256) + Chr(Int(n%(st) / 256))
Next st
com$ = com$ + Chr(16) + Chr(3)
tns% = tns% + 1
If tns% = 256 Then tns% = 0
CalcCRC com$
Form1.Comm1.Output = com$
st = Timer
Do
DoEvents
Loop While st + 3 > Timer And Form1.Comm1.InBufferCount < 2
Form1.Comm1.InputLen = 2
com$ = Form1.Comm1.Input
If com$ <> Chr(16) + Chr(6) Then
字串7
comunicating = False
Exit Function
End If
st = Timer
Do
DoEvents
Loop While st + 3 > Timer And Form1.Comm1.InBufferCount < 12
Form1.Comm1.Output = Chr(16) + Chr(6)
If Form1.Comm1.InBufferCount < 12 Then
comunicating = False
Exit Function
End If
Form1.Comm1.Output = Chr(16) + Chr(6)
WriteTable = True
comunicating = False
End Function
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