FAWEB.NET / OPC Server - OPC Client Labs

	SITEMAP PRIVACY JAPANESE

JAPAN	HOME \| Product \| Support \| Knowledge \| Download \| Sales \| Company \| Contact

You are Here : HOME > Product > OPC Server > Technical Guide - OPC Client Labs

BACK

OPC Client Labs

Forward

This page is explained with implementation of OPC Client program (VB6.0) accessing to OPC Server.

Notice
Concerning the specification of OPC is decided on OPC Foundation, the purpose of this page is that the implement user using our OPC Server can be easy to program.

We don't guarantee and support for sample code or description on this site. When using this code, please verify all functions enough.

The sample code will be able to download following.
OPC Client Sample opctestapp.zip(38KB)

	OPC Layer
OPC Server and Client application communicates through COM interface. The super class is OPC Server object. it will be able to access OPC Group Object or OPC Item object.

	Register OPC Automation DLL
When setup our OPC Server, some DLL is registered automatically. For access to OPC Server from Visual Basic, it needs to check "OPC Automation 2.0".

	Declare OPC Objects (OPC Server / OPC Group / OPC Item)
For hooking events of OPC Server, add to "WithEvents" in dimension statement or event handler named "OBJECTNAME_EVENTNAME". Dim WithEvents Myserver As OPCServer Dim WithEvents Mygroup As OPCGroup Dim WithEvents Mygroups As OPCGroups Dim Myitem As OPCItem Dim Myitems As OPCItems Dim MyBrowser As OPCBrowser

	Get OPC Server List
It is able to get installed OPC Server name by using OPC Server object. In this sample, it shows OPC Server name in list box and operator can select the target server. Dim Getserver As OPCServer Dim Servers As Variant Set Getserver = New OPCServer Servers = Getserver.GetOPCServers For i = LBound(Servers) To UBound(Servers) List1.AddItem Servers(i) Next i Set Getserver=Nothing

Connect and Browse

It is able to get device name registered in OPC Server by using OPC Server object. You can make the Group under device and OPC Server object is enabled to access this lower layer.

Create OPC Group Object and Add Tags

For accessing client application to physical device data, it needs to generate OPC Group object in OPC group collection. The OPC Group object can configure update interval of tags. Normally, the device of accessing same cycle will register in same group. Also, you should be carefully CPU performance to create over groups because OPC Server create a thread for each group.

Advise and Callback

Implements event handler of OPC Group object for advice mode. The OPC Server read data for each cycle and if changing the value, callback to client application. The quality flag is normally '0xC0', when occurred error, it will be turn to other value.

Sync Read/Write and ASync Read/Write

The OPC has two ways of data access, Synchronize and Asynchronous. In Synchronize, the client application must be wait for completing server work. But the client application can confirm server transaction is normally completed because the OPC Server returns the result on completing the communication work. This is a normally style of procedure.

In Asynchronous mode, the OPC Server turns the handle to client as soon as receiving the request and proceed the transaction on background. After completing this work, calls handler of client application. Asynchronous mode cut down wait time for communication and be able to run client application.
Caution: Asynchronous access is enabled under advice mode.

Mygroup.SyncRead OPCDevice, 16, ItemServerHandles, ItemValues, _
					ItemServerErrors, ItemQualities, ItemTimeStamps
For i = 1 To 16
  Debug.print ItemValues(i) + ":" + ItemTimeStamps(i) _
  + ":" + ItemQuality(i)
Next i

For i = 1 To 16
  ItemVal(i) = i
Next i
Mygroup.SyncWrite 16, ItemServerHandles, ItemVal, ItemServerErrors
For i = 1 To 16
  If ItemServerErrors(i) <> 0 Then
	MsgBox "Write ERROR " + Format(i)
  End If
Next i

Mygroup.AsyncRead 16, ItemServerHandles, ItemServerErrors, 10, 11

Private Sub Mygroup_AsyncReadComplete(ByVal TransactionID As Long, _
				 ByVal NumItems As Long, ClientHandles() As Long, _
				 ItemValues() As Variant, Qualities() As Long, _
				 TimeStamps() As Date, Errors() As Long)
  Debug.print "AsyncRead Comp" + Chr$(9) + Time$ + Chr$(13) + Chr$(10)
End Sub

Dim ItemVal(ItemCount) As Variant
For i = 1 To ItemCount
  ItemVal(i) = i
Next i
Mygroup.AsyncWrite 16, ItemServerHandles, ItemVal, _
	ItemServerErrors, 100, 101

Private Sub Mygroup_AsyncWriteComplete(ByVal TransactionID As Long, _
	   ByVal NumItems As Long, ClientHandles() As Long, Errors() As Long)
  Debug.print "AsyncWrite Comp" + Chr$(9) + Time$ + Chr$(13) + Chr$(10)
End Sub

Cache Read

In cache read operation, OPC Server doesn't access the physical device and return the last data on memory. The OPC Server read and caches the value every each time.It will be able to access on high speed if not need newest value.

BACK	Copyright © 1998-2006 TAKEBISHI Corporation All rights reserved.

TAKEBISHI Corporation
29 Mamedacho Nishikyogoku Ukyoku Kyoto 615-8501, JAPAN
TEL: +81-75-325-2171 / FAX: +81-75-325-2273 fa-support@takebishi.co.jp