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OPC Client Sample of Visual Basic 6.0

It introduces the easy sample program using the OPC Server. Please refer to here for a detailed explanation.

The sample program can be downloaded here.

	Sample Display
In this sample, it executes connecting to OPC Server, reading data automatically, reading data manually and writing data manually.

Sample Code

Option Explicit

Public OpcServer As IOPCServerDisp 'OPC Server object
Public OpcItemMgt As IOPCItemMgtDisp 'OPC group object
Public OpcItem As IOPCItemDisp 'OPC item object

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 
Private Sub CONNECT_Click()
	On Error GoTo problem
	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

' Create server object
	Set OpcServer = CreateObject(Form1.ServerName.Text)
	If TypeName(OpcServer) = TypeName(Nothing) Then Return 'no server

' Add a group
	Dim UpdateRate As Long
	Dim ServerHdl As Long
	UpdateRate = UpdateRateSet.Text ' Update Rate 1•b
	Set OpcItemMgt = OpcServer.AddGroup("Group One", True,
						  UpdateRate, 22, 1, 0, ServerHdl, UpdateRate)
	If TypeName(OpcItemMgt) = TypeName(Nothing) Then Return

' Add an item
	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

problem:
	MsgBox "Error connecting"
	For i% = 0 To ItemMax - 1
		Form1.Value(i%) = "Error"
	Next i%
End Sub

Private Sub Form_Load()
	Dim i%
	For i% = 0 To ItemMax - 1
		Form1.ItemName(i%).Text = "UC24.D" + Format$(i%)
	Next i%
End Sub

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
	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

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%
	io.OPCWrite ItemMax, ServerHandles, WriteValue, Errors
End Sub

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