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OPC Server是一套利用微软的COM/DCOM技术实现工业自动化资料获取的架构。OPC Server提供OPC接口，它将与之相连的物理设备（PLC）的信息值通过接口返回到客户端应用程序。也就是说，客户端通过这些接口，可以获得与OPC Server连接的物理设备的信息。对于集成应用程序，只要支持OPC接口，就能轻易访问物理设备，而无需相关的技术信息。 程序设计者可以使用相同的程序代码，操作不同的硬件装置，充分达成软件复用的目的。

它使用OPC Server引入了简单的示例程序。此示例的代码使用OPC 如果从.NET访问OPC Server，则需要交换COM和.NET的包装器。 自动化包装器（OPCDAAUTO.DLL），因此它几乎等于VB6.0。

Declaration

Option Explicit
Public OpcServer As IOPCServerDisp
Public OpcItemMgt As IOPCItemMgtDisp
Public OpcItem As IOPCItemDisp
Private Const ItemMax = 8
Private Const OPC_DS_CACHE = 1
Private Const OPC_DS_DEVICE = 2
Dim ClientHandles(ItemMax) As Long
Dim ServerHandles As Variant
Dim bConnect As Boolean

连接到OPC服务器，创建OPCGroup和添加标签

Private Sub CONNECT_Click()
 On Error GoTo err_hd
 Dim i%
 If bConnect Then
 CONNECT.Caption = "Connect"
 Set OpcServer = Nothing
 Set OpcItemMgt = Nothing
 Set OpcItem = Nothing
 bConnect = False
 READ_Button.Enabled = False
 WRITE_Button.Enabled = False
 For i% = ItemName.lbound To ItemName.ubound
 ItemName(i%).Enabled = True
 Next i%
 Exit Sub
 End If
 '*** Connect to OPC Server ***
 Set OpcServer = CreateObject(Form1.ServerName.Text)
 If TypeName(OpcServer) = TypeName(Nothing) Then Return
 '*** Add OPCGroup ***
 Dim UpdateRate As Long
 Dim ServerHdl As Long
 UpdateRate = UpdateRateSet.Text
 Set OpcItemMgt = OpcServer.AddGroup("Group One", True, UpdateRate, 22, 1, 0, ServerHdl, UpdateRate)
 If TypeName(OpcItemMgt) = TypeName(Nothing) Then Return
 '*** Add OPCItems ***
 Dim ItemIDs(ItemMax) As String
 Dim AccessPaths(ItemMax) As String
 Dim Active(ItemMax) As Boolean
 Dim Errors As Variant
 Dim ItemObjects As Variant
 Dim DataType(ItemMax) As Variant
 For i% = 0 To ItemMax - 1
 Active(i%) = True
 ClientHandles(i%) = 22 + i%
 AccessPaths(i%) = ""
 ItemIDs(i%) = Form1.ItemName(i%).Text
 DataType(i%) = 2
 Next i%
 OpcItemMgt.AddItems ItemMax, ItemIDs, Active,ClientHandles,
 ServerHandles, Errors, ItemObjects, AccessPaths, DataType
 Set OpcItem = ItemObjects(0)
 bConnect = True
 CONNECT.Caption = "DisConnect"
 READ_Button.Enabled = True
 WRITE_Button.Enabled = True
 For i% = ItemName.lbound To ItemName.ubound
 ItemName(i%).Enabled = False
 Next i%
 Exit Sub
err_hd:
 MsgBox "Error connecting"
 For i% = 0 To ItemMax - 1
 Form1.Value(i%) = "Error"
 Next i%
End Sub

缓存读取

Private Sub READ_Button_Click()
 Dim ReadValue As Variant
 Dim pQuality As Variant
 Dim pTimestamp As Variant
 Dim Errors As Variant
 Dim i%
 Dim io As IOPCSyncIODisp
 Set io = OpcItemMgt
 '*** Cache Read ***
 io.OPCRead OPC_DS_CACHE, ItemMax, ServerHandles, ReadValue, pQuality, pTimestamp, Errors
 For i% = 0 To ItemMax - 1
 Form1.Value(i%) = ReadValue(i%)
 pTimestamp(i%) = DateAdd("h", 9, pTimestamp(i%))
 Form1.Time(i%) = pTimestamp(i%)
 Form1.Quality(i%) = pQuality(i%)
 Next i%
End Sub

SyncWrite

Private Sub WRITE_Button_Click()
 Dim WriteValue(ItemMax) As Variant
 Dim io As IOPCSyncIODisp
 Dim Errors As Variant
 Dim i%
 Set io = OpcItemMgt
 For i% = 0 To ItemMax - 1
 WriteValue(i%) = Form1.Value(i%)
 Next i%
 '*** SyncWrite ***
 io.OPCWrite ItemMax, ServerHandles, WriteValue, Errors
End Sub

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