Data Access Automation Interface Standard.doc (Data Access Automation Interface Standard)

Data Access Automation Interface Standard Version 2.02 February 4, 1999 OPC Data Access Automation Specification2.02 Synopsis: This specification is an interface for developers of OPC clients and OPC Data Access Servers. The specification is a result of an analysis and design process to develop a standard interface to facilitate the development of servers and clients by multiple vendors that shall inter-operate seamlessly together. This document defines the OPC Data Access OLE Automation interface for developers of OPC clients and OPC Data Access Servers. The purpose of this specification is to provide an OLE Automation interface for the OPC Data Access Server Custom Interface Functionality Documentation Type Industry Standard Specification Title: OPC Data Access Automation Specification Date: February 3, 1999 Version: 2.02 Soft MS-Word Source: OPC Foundation Author: Status: Release Trademarks: Most computer and software brand names have trademarks or registered trademarks. The individual trademarks have not been listed here. Required Runtime Environment: This specification requires Windows 95/98 (with DCOM installed), Windows NT 4.0 or later. It is recommended that Windows NT 4.0 machines be run with SP3, or later. 2 OPC Data Access Automation Specification2.02 NON-EXCLUSIVE LICENSE AGREEMENT The OPC Foundation, a non-profit corporation (the “OPC Foundation”), has established a set of standard OLE/COM interface protocols intended to foster greater interoperability between automation/control applications, field systems/devices, and business/office applications in the process control industry. The current OPC specifications, prototype software examples and related documentation (collectively, the “OPC Materials”), form a set of standard OLE/COM interface protocols based upon the functional requirements of Microsoft’s OLE/COM technology. Such technology defines standard objects, methods, and properties for servers of real-time information like distributed process systems, programmable logic controllers, smart field devices and analyzers in order to communicate the information that such servers contain to standard OLE/COM compliant technologies enabled devices (e.g., servers, applications, etc.). The OPC Foundation will grant to you (the “User”), whether an individual or legal entity, a license to use, and provide User with a copy of, the current version of the OPC Materials so long as User abides by the terms contained in this Non-Exclusive License Agreement (“Agreement”). If User does not agree to the terms and conditions contained in this Agreement, the OPC Materials may not be used, and all copies (in all formats) of such materials in User’s possession must either be destroyed or returned to the OPC Foundation. 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This Agreement embodies the entire understanding between the parties with respect to, and supersedes any prior understanding or agreement (oral or written) relating to, the OPC Materials. 4 OPC Data Access Automation Specification2.02 Revision 2.0 Highlights This revision replaces the Data Access Automation Interface previously documented in the OPC Data Access 1.0A Specification. Basically the automation interface architecture was redesigned to address ease of use by Visual Basic Programmers, and to take advantage of the technology improvements, inclusive of automation events and object support for the WithEvents keyword. Revision 2.01 January 6, 1999 Highlights As noted elsewhere a draft version of the Specification was inadvertently circulated as Version 2.0. The 'correct' version 2.0 has been relabeled as 2.01 (this document), redated and republished. The basic changes between the draft dated October 14, 1998 and this document include:  Removal of AsyncRefreshComplete (event for refresh follows custom interface architecture, with data returned in DataChange Event);  Change to AsyncCancelComplete to return the Transaction ID associated with the method being canceled;  Changing reference to NumItems to Count;  Correction to OPC error numbering;  Adding NON-EXCLUSIVE LICENSE AGREEMENT Section;  Minor formatting changes. Revision 2.02 February 3, 1999 Minor correction to the CurrentPosition property description in the OPCBrowser Object. 5 OPC Data Access Automation Specification2.02 1 1.1 1.2 1.3 1.4 1.5 2 2.1 2.2 2.3 2.4 2.5 2.5.1 2.5.2 2.6 2.7 2.8 2.9 2.10 3 4 Table of Contents INTRODUCTION..................................................................................................10 BACKGROUND............................................................................................................................10 PURPOSE.......................................................................................................................................10 SCOPE............................................................................................................................................11 REFERENCES...............................................................................................................................11 AUDIENCE....................................................................................................................................11 ARCHITECTURE.................................................................................................12 FUNCTIONAL REQUIREMENTS...............................................................................................12 OPC AUTOMATION SERVER OBJECT MODEL.....................................................................13 OPC DATA ACCESS AUTOMATION OBJECT MODEL.........................................................13 DATA SYNCHRONIZATION......................................................................................................14 INTRODUCTION TO EXCEPTIONS AND EVENTS................................................................14 Exceptions...............................................................................................................................14 Events.....................................................................................................................................14 ARRAYS........................................................................................................................................14 COLLECTIONS.............................................................................................................................14 OPTIONAL PARAMETERS.........................................................................................................15 METHOD PARAMETERS............................................................................................................15 TYPE LIBRARY............................................................................................................................15 ABOUT THE OPC DATA ACCESS AUTOMATION WRAPPER DLL.......16 OPC DATA ACCESS AUTOMATION OBJECTS & INTERFACES............17 4.1 OPCSERVER OBJECT..................................................................................................................17 4.1.1 Summary of Properties...........................................................................................................17 4.1.2 Summary of Methods.............................................................................................................17 4.1.3 Summary of Events.................................................................................................................17 4.1.4 OPCServer Properties.............................................................................................................17 4.1.4.1 StartTime............................................................................................................................17 4.1.4.2 CurrentTime........................................................................................................................18 4.1.4.3 LastUpdateTime.................................................................................................................18 4.1.4.4 MajorVersion......................................................................................................................18 4.1.4.5 MinorVersion......................................................................................................................18 4.1.4.6 BuildNumber......................................................................................................................19 4.1.4.7 VendorInfo..........................................................................................................................19 4.1.4.8 ServerState..........................................................................................................................19 4.1.4.9 LocaleID.............................................................................................................................20 4.1.4.10 Bandwidth...........................................................................................................................20 4.1.4.11 OPCGroups.........................................................................................................................21 4.1.4.12 PublicGroupNames.............................................................................................................21 4.1.4.13 ServerName........................................................................................................................21 4.1.4.14 ServerNode.........................................................................................................................21 4.1.4.15 ClientName.........................................................................................................................22 4.1.5 OPCServer Methods...............................................................................................................22 6 OPC Data Access Automation Specification2.02 4.1.5.1 4.1.5.2 4.1.5.3 4.1.5.4 4.1.5.5 4.1.5.6 4.1.5.7 4.1.5.8 4.1.5.9 4.1.6 4.1.6.1 4.2 4.2.1 4.2.2 4.2.3 4.2.3.1 4.2.3.2 4.2.3.3 4.2.3.4 4.2.3.5 4.2.3.6 4.2.4 4.2.4.1 4.2.4.2 4.2.4.3 4.2.4.4 4.2.4.5 4.2.4.6 4.2.4.7 4.2.4.8 4.2.4.9 4.3 4.3.1 4.3.2 4.3.3 4.3.4 4.3.4.1 4.3.4.2 4.3.4.3 4.3.4.4 4.3.4.5 4.3.4.6 4.3.4.7 4.3.5 GetOPCServers...................................................................................................................22 Connect...............................................................................................................................23 Disconnect..........................................................................................................................24 CreateBrowser....................................................................................................................24 GetErrorString....................................................................................................................24 QueryAvailableLocaleIDs..................................................................................................25 QueryAvailableProperties...................................................................................................25 GetItemProperties...............................................................................................................26 LookupItemIDs...................................................................................................................27 OPCServer Events..................................................................................................................28 ServerShutDown.................................................................................................................28 OPCBROWSER OBJECT..............................................................................................................30 Summary of Properties...........................................................................................................31 Summary of Methods.............................................................................................................31 OPCBrowser Properties..........................................................................................................31 Organization.......................................................................................................................31 Filter....................................................................................................................................31 DataType.............................................................................................................................32 AccessRights.......................................................................................................................32 CurrentPosition...................................................................................................................33 Count...................................................................................................................................33 OPCBrowser Methods............................................................................................................33 Item.....................................................................................................................................33 ShowBranches....................................................................................................................34 ShowLeafs..........................................................................................................................34 MoveUp..............................................................................................................................35 MoveToRoot.......................................................................................................................35 MoveDown.........................................................................................................................35 MoveTo...............................................................................................................................35 GetItemID...........................................................................................................................36 GetAccessPaths...................................................................................................................36 OPCGROUPS OBJECT.................................................................................................................38 Summary of Properties...........................................................................................................38 Summary of Methods.............................................................................................................38 Summary of Events.................................................................................................................38 OPCGroups Properties............................................................................................................39 Parent..................................................................................................................................39 DefaultGroupIsActive.........................................................................................................39 DefaultGroupUpdateRate...................................................................................................39 DefaultGroupDeadband......................................................................................................40 DefaultGroupLocaleID.......................................................................................................40 DefaultGroupTimeBias.......................................................................................................40 Count...................................................................................................................................41 OPCGroups Methods..............................................................................................................41 7 OPC Data Access Automation Specification2.02 4.3.5.1 Item.....................................................................................................................................41 4.3.5.2 Add.....................................................................................................................................41 4.3.5.3 GetOPCGroup.....................................................................................................................42 4.3.5.4 Remove...............................................................................................................................42 4.3.5.5 RemoveAll..........................................................................................................................43 4.3.5.6 ConnectPublicGroup...........................................................................................................43 4.3.5.7 RemovePublicGroup...........................................................................................................43 4.3.6 OPCGroups Events.................................................................................................................44 4.3.6.1 GlobalDataChange..............................................................................................................44 4.4 OPCGROUP OBJECT...................................................................................................................46 4.4.1 Summary of Properties...........................................................................................................46 4.4.2 Summary of Methods.............................................................................................................46 4.4.3 Summary of Events.................................................................................................................46 4.4.4 OPCGroup Properties.............................................................................................................47 4.4.4.1 Parent..................................................................................................................................47 4.4.4.2 Name...................................................................................................................................47 4.4.4.3 IsPublic...............................................................................................................................48 4.4.4.4 IsActive...............................................................................................................................48 4.4.4.5 IsSubscribed........................................................................................................................49 4.4.4.6 ClientHandle.......................................................................................................................49 4.4.4.7 ServerHandle......................................................................................................................50 4.4.4.8 LocaleID.............................................................................................................................50 4.4.4.9 TimeBias.............................................................................................................................51 4.4.4.10 DeadBand...........................................................................................................................51 4.4.4.11 UpdateRate.........................................................................................................................52 4.4.4.12 OPCItems............................................................................................................................52 4.4.5 OPCGroup Methods...............................................................................................................52 4.4.5.1 SyncRead............................................................................................................................52 4.4.5.2 SyncWrite...........................................................................................................................54 4.4.5.3 AsyncRead..........................................................................................................................55 4.4.5.4 AsyncWrite.........................................................................................................................56 4.4.5.5 AsyncRefresh......................................................................................................................58 4.4.5.6 AsyncCancel.......................................................................................................................59 4.4.6 OPCGroup Events..................................................................................................................59 4.4.6.1 DataChange.........................................................................................................................59 4.4.6.2 AsyncReadComplete..........................................................................................................60 4.4.6.3 AsyncWriteComplete.........................................................................................................61 4.4.6.4 AsyncCancelComplete.......................................................................................................61 4.5 OPCITEMS OBJECT.....................................................................................................................63 4.5.1 Summary of Properties...........................................................................................................63 4.5.2 Summary of Methods.............................................................................................................63 4.5.3 OPCItems Properties..............................................................................................................64 4.5.3.1 Parent..................................................................................................................................64 4.5.3.2 DefaultRequestedDataType................................................................................................64 8 OPC Data Access Automation Specification2.02 4.5.3.3 DefaultAccessPath..............................................................................................................64 4.5.3.4 DefaultIsActive...................................................................................................................65 4.5.3.5 Count...................................................................................................................................65 4.5.4 OPCItems Methods.................................................................................................................65 4.5.4.1 Item.....................................................................................................................................65 4.5.4.2 GetOPCItem.......................................................................................................................66 4.5.4.3 AddItem..............................................................................................................................66 4.5.4.4 AddItems.............................................................................................................................67 4.5.4.5 Remove...............................................................................................................................68 4.5.4.6 Validate...............................................................................................................................68 4.5.4.7 SetActive.............................................................................................................................69 4.5.4.8 SetClientHandles................................................................................................................70 4.5.4.9 SetDataTypes......................................................................................................................70 4.6 OPCITEM OBJECT.......................................................................................................................72 4.6.1 Summary of Properties...........................................................................................................72 4.6.2 Summary of Methods.............................................................................................................72 4.6.3 OPCItem Properties................................................................................................................72 4.6.3.1 Parent..................................................................................................................................72 4.6.3.2 ClientHandle.......................................................................................................................72 4.6.3.3 ServerHandle......................................................................................................................73 4.6.3.4 AccessPath..........................................................................................................................73 4.6.3.5 AccessRights.......................................................................................................................73 4.6.3.6 ItemID.................................................................................................................................74 4.6.3.7 IsActive...............................................................................................................................74 4.6.3.8 RequestedDataType............................................................................................................74 4.6.3.9 Value...................................................................................................................................75 4.6.3.10 Quality................................................................................................................................75 4.6.3.11 TimeStamp..........................................................................................................................75 4.6.3.12 CanonicalDataType............................................................................................................75 4.6.3.13 EUType...............................................................................................................................76 4.6.3.14 EUInfo................................................................................................................................76 4.6.4 OPCItem Methods..................................................................................................................76 4.6.4.1 Read....................................................................................................................................76 4.6.4.2 Write...................................................................................................................................77 5 5.1 5.2 5.3 5.4 5.5 6 7 8 OPC DATA ACCESS AUTOMATION DEFINITIONS AND SYMBOLS.....79 OPCNAMESPACETYPES............................................................................................................79 OPCDATASOURCE......................................................................................................................79 OPCACCESSRIGHTS...................................................................................................................79 OPCSERVERSTATE.....................................................................................................................79 OPCERRORS.................................................................................................................................79 APPENDIX A - OPC AUTOMATION ERROR HANDLING.........................81 APPENDIX B – SAMPLE STRING FILTER SYNTAX FUNCTION.............83 APPENDIX C - DATA ACCESS AUTOMATION IDL SPECIFICATION...85 9 OPC Data Access Automation Specification2.02 9 APPENDIX D- NOTES ON AUTOMATION DATA TYPES........................100 10 OPC Data Access Automation Specification2.02 1 1.1 Introduction Background A standard mechanism for communicating to numerous data sources, either devices on the factory floor, or a database in a control room is the motivation for this specification. The standard mechanism would consist of a standard automation interface targeted to allow Visual Basic applications, as well as other automation enabled applications to communicate to the above named data sources. Manufacturers need to access data from the plant floor and integrate it into their existing business systems. Manufacturers must be able to utilize off the shelf tools (SCADA Packages, Databases, spreadsheets, etc.) to assemble a system to meet their needs. The key is open and effective communication architecture concentrating on data access, and not the types of data. We have addressed this need by architecting and specifying a standard automation interface to the OPC Data Access Custom interface to facilitate the need s of applications that utilize an automation interface to access plant floor data. 1.2 Purpose What is needed is a common way for automation applications to access data from any data source like a device or a database. The OPC Data Access Automation defines a standard by which automation applications can access process data. This interface provides the same functionality as the custom interface, but in an “automation friendly” manner. Given the common use of Automation to access other software environments (e.g.: RDBMS, MS Office applications, WWW objects), this interface has been tailored to ease application development, without sacrificing functionality defined by the Custom interface. The figure below shows an Automation client calling into an OPC Data Access Server using a 'wrapper' DLL. This wrapper translates between the custom interface provided by the server and the automation interface desired by the client. Note that in general the connection between the Automation Client and the Automation Server will be 'In Process' while the connection between the Automation Server and the Custom Server may be either In Process, Local or Remote. Automation Client OPC Automation Wrapper COM / DCOM OPC Custom Interface Server Figure 1-1. Custom and Automation Client Applications Interfacing to OPC Servers 11 OPC Data Access Automation Specification2.02 1.3 Scope This document specifies a revised version of the OLE Automation interface that was specified in Release 1.0 of the OPC specification. There were several reasons for these revisions. The most important are as follows:  Make the interface easier to use by the Visual Basic Programmer  Take advantage of newer features of Visual Basic (such as events)  Allow the creation of a common wrapper DLL which could be shared by all vendors This document assumes that the reader is familiar with the information provided on the OPC Data Access Custom Interface Specification. That document provides an Overview of the OPC functionality as well as detailed descriptions of the behavior of the various functions. We have deliberately not duplicated that information in an attempt to maintain consistency. 1.4 References Kraig Brockschmidt, Inside OLE, Second Edition, Microsoft Press, Redmond, WA, 1995. Microsoft Systems Journal, Q&A, April 1996, pp. 89-101. OLE Automation Programming Reference, Microsoft Press, Redmond, WA, 1996. OLE 2 Programming Reference, Vol. 1, Microsoft Press, Redmond, WA, 1994. OPC Data Access Custom Interface Standard, Version 2.0, OPC Foundation 1998. 1.5 Audience This specification is intended as reference material for developers of OPC Automation Clients that require the functionality of the OPC Data Access Custom Interface. The developer needs some knowledge of basic Automation concepts and terminology. 12 OPC Data Access Automation Specification2.02 2 Architecture The fundamental design goal is that this interface is intended to work as a 'wrapper' for existing OPC Data Access Custom Interface Servers providing an automation friendly mechanism to the functionality provided by the custom interface. 2.1    Functional Requirements The automation interface provides nearly all of the functionality of the required and optional Interfaces in the OPC Data Access Custom Interface. If the OPC Data Access Custom server supports the interface, the functions and properties at the automation level will work. Automation interfaces generally do not support optional capabilities in the same way that the custom interface does. If the underlying custom interface omits some optional functionality then the corresponding automation functions and properties will exhibit some reasonable default behavior as described in more detail later in this document. The interfaces are fully supported by VC++ and Visual Basic 5.0. They allow any application which has an OLE Automation Interface (e.g. VB, VC++, and VBA enabled applications) to access the OPC Interface, according to the limitations of the respective application. The interface described in this specification specifically does NOT support VBScript or Java Script. A separate wrapper could be developed to accommodate the needs of VBScript and Java Script. However such an effort is outside the scope of this specification. 13 OPC Data Access Automation Specification2.02 2.2 OPC Automation Server Object Model OPCServer OPCGroups (collection) OPCBrowser OPCGroup OPCItems (collection) OPCItem Figure 2-1. Automation Object Hierarchy 2.3 Object Description OPCServer An instance of an OPC Server. You must create an OPCServer object before you can get references to other objects. It contains the OPCGroups Collection and creates OPCBrowser objects. OPCGroups An Automation collection containing all of the OPCGroup objects this client has created within the scope of the OPCServer that the Automation Application has connected to via the OPCServer.Connect() OPCGroup An instance of an OPCGroup object. The purpose of this object is to maintain state information and provide the mechanism to provide data acquisition services for the OPCItem Collection object that the OPCGroup object references. OPCItems An Automation collection containing all of the OPCItem objects this client has created within the scope of the OPCServer, and corresponding OPCGroup object that the Automation Application has created. OPCItem An automation object that maintains the item’s definition, current value, status information, last update time. Note the Custom Interface does not provide a separate Item Object. OPCBrowser An object that browses item names in the server’s configuration. There exists only one instance of an OPCBrowser object per instance of an OPC Server object. OPC Data Access Automation Object Model The OPCServer object provides a way to access (read/write) or communicate to a set of data sources. The types of sources available are a function of the server implementation. 14 OPC Data Access Automation Specification2.02 An OPC Automation client connects to an OPC Automation Server that communicates to the underlying data source (e.g. OPC Data Access Custom Servers) through the functionality provided by the automation objects described here. The OPCServer provides an (OPCGroups) automation collection object to maintain a collection of OPCGroup Objects. The OPCGroup object allows clients to organize the data they want to access. An OPCGroup can be activated and deactivated as a unit. An OPCGroup also provides a way for the client to ‘subscribe’ to the list of items so that it can be notified when they change. The OPCGroup Object provides an OPCItems collection of OPCItems. The OPCItem object provides a connection to a single data item in the underlying data source. 2.4 Data Synchronization There is a requirement that the VB client be able to read or receive data such that the value, quality, and timestamp information are kept in sync. Basically the client needs to be assured that the quality of the data and the timestamp matches the value. If a client obtains values using any of the Read methods it can be assured that Value, Timestamp, and Quality properties will be in synch with each other. If a client obtains data by registering for DataChange events, then the Value, Timestamp, and Quality will be in sync within the scope of the EventHandler routine. If a client mixes these two approaches it will be impossible for the client to ensure that the item properties are exactly in sync since an event which changed the properties could occur between the time the client accesses the various properties. 2.5 Introduction to Exceptions and Events 2.5.1 Exceptions Most properties and methods described here communicate with an OPC Custom Server. In OLE Automation, there is no easy way to return an error when accessing a property. The best way to resolve this is for the automation server to generate an exception if such an error occurs in the underlying data source. This means that the client needs to have exception logic in place to handle errors. Errors that occur when setting a property are reported using the standard Visual Basic Err object. Refer to Appendix A OPC Automation Error Handling for more details on handling errors. 2.5.2 Events The automation interface supports the event notification mechanism that is provided with Visual Basic 5.0. The Automation server triggers events in response to Async Refresh, Async Read and Async Write Method calls. In addition, Automation server triggers events when data changes according to the client specification. The implementation assumes that the Automation Client is equipped to deal with these events. 2.6 Arrays By convention, the OPC Automation interface assumes that arrays are 1 based. If an array is passed to a function that is larger than the Count or NumItems parameter, only Count or NumItems elements will be used, starting at index 1. This only applies to parameters for functions and events within the automation interface. This does not apply to item values, where the data type for the item value is itself an array. To avoid errors it is suggested that VB code use “Option Base 1”. 2.7 Collections OLE Automation collections are objects that support Count, Item, and a hidden property called _NewEnum. Any object that has these properties as part of the interface can be called a collection. In VB, a collection can be iterated using either of two idioms. The first method explicitly uses Count and Item to index the elements of the collection. 15 OPC Data Access Automation Specification2.02 For I = 1 To object.Count element = object.Item ( I ) ‘or… element = object( I ) Next I The second method iterates through the available items using the hidden _NewEnum function: For Each element In object ‘do something with element Next element The For Each method of iterating a collection is faster than the explicit Item method. Item can also be used to access a particular index, such as Item( 3 ). It doesn’t need to be used within a loop. 2.8 Optional Parameters Optional parameters are denoted by the keyword “Optional”. Optional parameters may be omitted from a method call if the default behavior is acceptable. OLE Automation requires that optional parameters be Dim’d as Variant, though they may hold a string, array, etc. 2.9 Method Parameters Method parameters are assumed to be passed ByVal unless specified to be ByRef. ByRef parameters get filled in by the method and passed back. 2.10 Type Library VB uses the OPC Automation Type Library to define the following interfaces. Make sure that (in Visual Basic 5.0) Properties | References has “OPC Automation 2.0” checked. 16 OPC Data Access Automation Specification2.02 3 About the OPC Data Access Automation Wrapper DLL The OPC foundation has provided a reference sample of the Data Access Automation interface for the OPC foundation members use in providing an automation interface to OPC data access custom interface servers. The reference sample is provided as a DLL complete with the Visual C++ source code. Vendors may provide the DLL directly with their product. Vendors that choose to modify the source code, or even just build the DLL from the source code(unchanged) must do the following prior to including or shipping the DLL. 1. The name of the OPC automation DLL must be changed from OPCDAAuto.dll to a vendor specific unique name. 2. The name of the OPC automation IDL(opcauto.idl) file should be changed to a vendor specific unique name. 3. The helpstring ("OPC Automation 2.0") in the IDL file must be changed to reflect your vendor specific OPC automation interface. This is the name that shows up in the Automation Type Library. Visual Basic applications that use your vendor build OPC automation interface DLL will include the DLL by using the type library. 4. All guid’s in the IDL file must be changed to new values that are generated by using the Guidgen tool. This is required to prevent the vendor built automation interface library from being confused with another vendors built automation library or the OPC foundation provided automation library. The vendor is encouraged to not change the existing automation interfaces. If additional functionality is desired, a new object and interface should be added and should replicate all the functionality of the existing object that is being added to. The OPC foundation has also provide a visual basic sample that demonstrates usage of the Data Access Automation interface. This sample is intended only to demonstrate the functionality of the OPC data access automation interface. 17 OPC Data Access Automation Specification2.02 4 OPC Data Access Automation Objects & Interfaces 4.1 OPCServer Object Description A client creates the OPCServer Automation object. The client then 'connects' it to an OPC Data Access Custom Interface (see the 'Connect' method). The OPCServer object can now be used to obtain general information about an OPC server and to create and manipulate the collection of OPCGroup objects.' Syntax OPCServer Remarks The WithEvents syntax enables the object to support the declared events for the particular object. For the OPCServer, the only event defined is the ServerShutDown. The OPCGroup (described later) has all the events associated with DataChange and the events as required to support the Asynchronous methods of the OPCGroup object. Example Dim WithEvents AnOPCServer As OPCServer Set AnOPCServer = New OPCServer 4.1.1 Summary of Properties StartTime MajorVersion CurrentTime MinorVersion LastUpdateTime BuildNumber VendorInfo Bandwidth ServerState OPCGroups LocaleID PublicGroupNames ServerName ServerNode ClientName GetOPCServers Connect Disconnect CreateBrowser QueryAvailableProperties GetErrorString GetItemProperties QueryAvailableLocaleIDs LookupItemIDs 4.1.2 4.1.3 Summary of Methods Summary of Events ServerShutDown 4.1.4 OPCServer Properties 4.1.4.1 StartTime Description (Read-only) Returns the time the server started running. This is the start time of the server that the client has specified to connect to. Multiple Clients connecting to the same server can be assured that each client will read the same value from the server for this property. Syntax StartTime As Date Remarks The automation server is expected to use the custom interface GetStatus () to obtain the values for this property as well as many of the other properties defined as properties of the OPCServer. An error occurs if the client has not connected to a Data Access Server via the Connect method. Example Dim AnOPCServerTime As Date 18 OPC Data Access Automation Specification2.02 AnOPCServerTime = AnOPCServer.StartTime 4.1.4.2 CurrentTime Description (Read-only) Returns the current time from the server. When you access this property, you will get the value that the automation server has obtained from the custom server via the GetStatus () interface. Syntax CurrentTime As Date Remarks An error occurs if the client has not connected to a Data Access Server via the Connect method. Example Dim AnOPCServerTime As Date AnOPCServerTime = AnOPCServer.CurrentTime 4.1.4.3 LastUpdateTime Description (Read-only) Returns the last update time from the server. When you access this property, you will get the value that the automation server has obtained from the custom server via the GetStatus() interface. Syntax LastUpdateTime As Date Remarks Returns the last time data was sent from the server to a client application. An error occurs if the client has not connected to a Data Access Server via the Connect method. Example Dim AnOPCServerTime As Date AnOPCServerTime = AnOPCServer.LastUpdateTime 4.1.4.4 MajorVersion Description (Read-only) Returns the major part of the server version number (e.g. the “1” in version 1.32). When you access this property, you will get the value that the automation server has obtained from the custom server via the GetStatus() interface. Syntax MajorVersion As Integer Remarks An error occurs if the client has not connected to a Data Access Server via the Connect method. Example Dim AnOPCServerMajorVersion As String AnOPCServerMajorVersion = Str(AnOPCServer.MajorVersion) 4.1.4.5 MinorVersion Description (Read-only) Returns the minor part of the server version number (e.g. the “32” in version 1.32). When you access this property, you will get the value that the automation server has obtained from the custom server via the GetStatus () interface. Syntax MinorVersion As Integer Remarks An error occurs if the client has not connected to a Data Access Server via the Connect method. 19 OPC Data Access Automation Specification2.02 Example Dim AnOPCServerMinorVersion As String AnOPCServerMinorVersion = Str(AnOPCServer.MinorVersion) 4.1.4.6 BuildNumber Description (Read-only) Returns the build number of the server. When you access this property, you will get the value that the automation server has obtained from the custom server via the GetStatus () interface. Syntax BuildNumber As Integer Remarks An error occurs if the client has not connected to a Data Access Server via the Connect method. Example Dim BuildNumber as Integer BuildNumber = AnOPCServer.BuildNumber 4.1.4.7 VendorInfo Description (Read-only) Returns the vendor information string for the server. When you access this property, you will get the value that the automation server has obtained from the custom server via the GetStatus () interface. Syntax VendorInfo As String Remarks An error occurs if the client has not connected to a Data Access Server via the Connect method. Example Dim info As String info = AnOPCServer.VendorInfo 4.1.4.8 ServerState Description (Read-only) Returns the server’s state, which will be one of the OPCServerState values: Syntax ServerState As Long Setting Description OPC_STATUS_RUNNING The server is running normally. This is the usual state for a server OPC_STATUS_FAILED A vendor specific fatal error has occurred within the server. The server is no longer functioning. The recovery procedure from this situation is vendor specific. An error code of E_FAIL should generally be returned from any other server method. OPC_STATUS_NOCONFIG The server is running but has no configuration information loaded and thus cannot function normally. Note this state implies that the server needs configuration information in order to function. Servers which do not require configuration information should not return this state. OPC_STATUS_SUSPENDED The server has been temporarily suspended via some vendor 20 OPC Data Access Automation Specification2.02 specific method and is not getting or sending data. Note that Quality will be returned as OPC_QUALITY_OUT_OF_SERVICE. OPC_STATUS_TEST The server is in Test Mode. The outputs are disconnected from the real hardware but the server will otherwise behave normally. Inputs may be real or may be simulated depending on the vendor implementation. Quality will generally be returned normally. Remarks These are the server states that are described in the OPC Data Access Custom Interface Specification, and returned by an OPC server via the custom interface. Refer to the OPC Data Access Custom Interface Specification IOPCServer::GetStatus() for more details. When you access this property, you will get the value that the automation server has obtained from the custom server via the GetStatus () interface. An error occurs if the client has not connected to a Data Access Server via the Connect method.. Example Dim ServerState As Long ServerState = AnOPCServer.ServerState 4.1.4.9 LocaleID Description (Read/Write) This property identifies the locale, which may be used to localize strings returned from the server. . This LocaleID will be used by the GetErrorString method on this interface Syntax LocaleID As Long Remarks It should also be used as the ‘default’ LocaleID by any other server functions that are affected by LocaleID. An error occurs if the client has not connected to a Data Access Server via the Connect method. Example ‘(getting the property):: Dim LocaleID As Long LocaleID = AnOPCServer.LocaleID ‘(setting the property): AnOPCServer.LocaleID = LocaleID 4.1.4.10 Bandwidth Description (Read-only) This is server specific. The suggested use is the server’s bandwidth as a percentage of available bandwidth. This value will be hFFFFFFFF when the server cannot calculate a bandwidth. When you access this property, you will get the value that the automation server has obtained from the custom server via the GetStatus () interface. Syntax Bandwidth As Long Remarks An error occurs if the client has not connected to a Data Access Server via the Connect method. Example Dim Bandwidth As Long Bandwidth = AnOPCServer.Bandwidth 21 OPC Data Access Automation Specification2.02 4.1.4.11 OPCGroups Description (Read only) A collection of OPCGroup objects. This is the default property of the OPCServer object. Syntax OPCGroups As OPCGroups Example ‘(explicit property specification): Dim groups As OPCGroups Set groups = AnOPCServer.OPCGroups ‘(using the default specification): Dim groups As OPCGroups Set groups = AnOPCServer 4.1.4.12 PublicGroupNames Description (Read-only) Returns the names of this server’s Public Groups. These names can be used in ConnectPublicGroup. The names are returned as an array of strings. Syntax PublicGroupNames As Variant Remarks An error occurs if the client has not connected to a Data Access Server via the Connect method. An empty list is returned if the underlying server does not support the Public Groups interface, or if there are no public groups defined. Example Dim AllPublicGroupNames As Variant AllPublicGroupNames = AnOPCServer.PublicGroupNames 4.1.4.13 ServerName Description (Read-only) Returns the server name of the server that the client connected to via Connect(). Syntax ServerName As String Remarks When you access this property, you will get the value that the automation server has cached locally. The ServerName is empty if the client is not connected to a Data Access Server. Example Dim info As String info = AnOPCServer.ServerName 4.1.4.14 ServerNode Description (Read-only) Returns the node name of the server that the client connected to via Connect(). When you access this property, you will get the value that the automation server has cached locally. Syntax ServerNode As String 22 OPC Data Access Automation Specification2.02 Remarks The ServerNode is empty if the client is not connected to a Data Access Server. The ServerNode will be empty if no host name was specified in the Connect method. Example Dim info As String info = AnOPCServer.ServerNode 4.1.4.15 ClientName Description (Read/Write) This property allows the client to optionally register a client name with the server. This is included primarily for debugging purposes. The recommended behavior is that the client set his Node name and EXE name here. Syntax ClientName As String Remarks Recommended to put NodeName and ClientName in the string, separated by a semi-colon (;). Refer to the example below for suggested syntax Example ‘(getting the property): Dim info As String info = AnOPCServer.ClientName ‘(setting the property): AnOPCServer.ClientName = “NodeName;c:\programfiles\vendor\someapplication.exe” 4.1.5 OPCServer Methods 4.1.5.1 GetOPCServers Description Returns the names (ProgID’s) of the registered OPC Servers. Use one of these ProgIDs in the Connect method. The names are returned as an array of strings. Syntax GetOPCServers(Optional Node As Variant) As Variant Remarks Part Description Node The Node name provides the mechanism to specify the remote node where you want the automation server to give you the list of all the registered OPC servers. Refer to the OPC Data Access Custom Interface Standard for specific registry requirements for the custom servers. Node is optional. The use of a node name makes use of DCOM to access another computer. Acceptable node names are UNC names (“Server”), or DNS names (“server.com”, “www.vendor.com”, or “180.151.19.75”). Example ‘ getting the registered OPC Servers (the real OPC servers and adding them to a standard VB listbox). Dim AllOPCServers As Variant AllOPCServers = AnOPCServer.GetOPCServers 23 OPC Data Access Automation Specification2.02 For i = LBound(AllOPCServers) To UBound(AllOPCServers) listbox.AddItem AllOPCServers(i) Next i 4.1.5.2 Connect Description Must be called to establish connection to an OPC Data Access Server (that implements the custom interface). Syntax Connect (ProgID As String, Optional Node As Variant) Remarks Part Description ProgID The ProgID is a string that uniquely identifies the registered real OPC Data Access Server (that implements the custom interface). Node The Node name can specify another computer to connect using DCOM. Each instance of an OPC Automation Server is “connected” to an OPC Data Access Server (which implements the custom interface). Node is optional. The use of a node name makes use of DCOM to access another computer. Acceptable node names are UNC names (“Server”), or DNS names (“server.com”, “www.vendor.com”, or “180.151.19.75”). Calling this function will result in the automation wrapper calling CoCreateInstanceEx to create a Data Access Custom(specified by the ProgID )server on the specified machine(StrNodeName). If this function is called a second time without calling explicitly calling disconnect the automation wrapper will automatically disconnect the existing connection. See Also Use the GetOPCServers method to find the legal ProgIDs. Example ‘ Connect to the first registered OPCServer returned from the GetOPCServers Dim AllOPCServers As Variant AllOPCServers = AnOPCServer.GetOPCServers AnOPCServer.Connect(AllOPCServers(1)) ‘Connect to a specific server on some remote node Dim ARealOPCServer As String Dim ARealOPCNodeName As String ARealOPCServer = “VendorX.DataAccessCustomServer” ARealOPCNodeName = “SomeComputerNodeName” AnOPCServer.Connect (ARealOPCServer, ARealOPCNodeName) 24 OPC Data Access Automation Specification2.02 4.1.5.3 Disconnect Description Disconnects from the OPC server. Syntax Disconnect() Remarks This allows you to disconnect from a server and then either connect to another server, or remove the object. It is it is good programming practice for the client application to explicitly remove the objects that it created (including all OPCGroup(s), and OPCItem(s) using the appropriate automation method. Calling this function will remove all of the groups and release all references to the underlying OPC Custom Server. Example AnOPCServer.Disconnect 4.1.5.4 CreateBrowser Description Creates an OPCBrowser object Syntax CreateBrowser() As OPCBrowser Remarks The OPC Browse interface is an optional interface that is not required to be supported by an OPC Custom interface server. Therefore, an OPCBrowser object will not be returned for OPC Custom interface servers that do not implement the browse interface. Example Dim ARealOPCServer As String Dim ARealOPCNodeName As String ARealOPCServer = “VendorX.DataAccessCustomServer” ARealOPCNodeName = “SomeComputerNodeName” AnOPCServer.Connect(ARealOPCServer, ARealOPCNodeName) Dim AnOPCServerBrowserObject As OPCBrowser Set AnOPCServerBrowserObject = AnOPCServer.CreateBrowser 4.1.5.5 GetErrorString Description Converts an error number to a readable string. The server will return the string in the Locale that is specified in the server level LocaleID property. Refer to the properties of the OPC Server for setting and getting the LocaleID property. Syntax GetErrorString(ErrorCode As Long ) As String Example Part Description ErrorCode Server specific error code that the client application had returned from an interface function from the server, and for which the client application is requesting the server’s textual representation. Dim AnOPCServerErrorString As String ‘ for this sample, assume while adding some items, we detected that one of the items was ‘invalid. 25 OPC Data Access Automation Specification2.02 Not all code included for clarity reasons. AnOPCItemCollection.Add AddItemCount, AnOPCItemIDs, AnOPCItemServerHandles, AnOPCItemErrors ’Get the error string and display it to tell the user why the item could not be added AnOPCServerErrorString = AnOPCServer.GetErrorString(AnOPCItemErrors (index)) ‘and more code ErrorBox.Text = AnOPCServerErrorString ‘and more code 4.1.5.6 QueryAvailableLocaleIDs Description Return the available LocaleIDs for this server/client session. The LocaleIDs are returned as an array of longs. Syntax QueryAvailableLocaleIDs () As Variant Example Dim LocaleID As Variant Dim AnOPCTextSting as String AnOPCServerLocaleID = AnOPCServer.QueryAvailableLocaleIDs() For i = LBound(LocaleID) To UBound(LocaleID) AnOPCTextSting = LocaleIDToString(LocaleID(i)) listbox.AddItem AnOPCTextSting Next i 4.1.5.7 QueryAvailableProperties Description Return a list of ID codes and Descriptions for the available properties for this ItemID. This list may differ for different ItemIDs. This list is expected to be relatively stable for a particular ItemID. That is, it could be affected from time to time by changes to the underlying system’s configuration. Syntax QueryAvailableProperties (ItemID As String, ByRef Count As Long, ByRef PropertyIDs() as Long, ByRef Descriptions() As String, ByRef DataTypes() As Integer) Part Description ItemID The ItemID for which the caller wants to know the available properties Count The number of properties returned PropertyIDs DWORD ids for the returned properties. These IDs can 26 OPC Data Access Automation Specification2.02 be passed to GetItemProperties or LookupItemIDs Descriptions A brief vendor supplied text Description of each Property. NOTE LocalID does not apply to Descriptions. DataTypes The datatype which will be returned for this Property by GetItemProperties. Example ‘ Get the available properties Dim OPCItemID As String Dim ItemCount As Long Dim PropertyIDs() As Long Dim Descriptions() As String Dim DataTypes() As Integer Dim AnOPCTextSting As String OPCItemID = “SomeOPCDataAccessItem” AnOPCServer.QueryAvailableProperties (OPCItemID, ItemCount, PropertyIDs, Descriptions, DataTypes) For i = 1 To ItemCount AnOPCTextSting = Str(PropertyIDs(i) + “ “ + Descriptions(i) listbox.AddItem AnOPCTextSting Next I 4.1.5.8 GetItemProperties Description Return a list of the current data values for the passed ID codes. Syntax GetItemProperties (ItemID As String, Count As Long, ByRef PropertyIDs() as Long, ByRef PropertyValues() As Variant, ByRef Errors() As Long) Part Description ItemID The ItemID for which the caller wants to read the list of properties Count The number of properties passed PropertyIDs DWORD ids for the requested properties. These IDs were returned by QueryAvailableProperties or obtained from 27 OPC Data Access Automation Specification2.02 the fixed list described earlier. PropertyValue s An array of size Count VARIANTS returned by the server, which contain the current values of the requested properties. Errors Error array indicating whether each property was returned. Example Dim OPCItemID as String Dim ItemCount As Long Dim PropertyIDs(3) as Long Dim Data() as Variant Dim Errors() as Long Dim AnOPCTextSting As String ‘ Set values for ItemCount and PropertyIDs… AnOPCServer.GetItemProperties (OPCItemID, ItemCount, PropertyIDs, Data, Errors) For i = 1 To ItemCount AnOPCTextSting = Str(PropertyIDs(i) + “ “ + Data(i) listbox.AddItem AnOPCTextSting Next i 4.1.5.9 LookupItemIDs Description Return a list of ItemIDs (if available) for each of the passed ID codes. These indicate the ItemID, which could be added to an OPCGroup and used for more efficient access to the data corresponding to the Item Properties. An error within the error array may indicate that the passed Property ID is not defined for this item. Syntax LookupItemIDs (ItemID As String, Count As Long, PropertyIDs() as Long, ByRef NewItemIDs() As String, ByRef Errors () As Long) ItemID The ItemID for which the caller wants to lookup the list of properties Count The number of properties passed PropertyIDs DWORD ids for the requested properties. These IDs were returned by QueryAvailableProperties 28 OPC Data Access Automation Specification2.02 NewItemID s The returned list of ItemIDs. Errors Error array indicating whether each New ItemID was returned. Example Dim OPCItemID as String Dim Count As Long Dim PropertyIDs(1) as Long Dim NewItemIDs () as String Dim Errors() as Long Dim AnOPCTextSting As String OPCItemID = “SomeOPCDataAccessItem” Count = 1 PropertyIDs(1) = 5; AnOPCServer.LookupItemIDs (OPCItemID, Count, PropertyIDs, NewItemIDs, Errors) For i = 1 To Count AnOPCTextSting = Str(PropertyIDs(i) + “ “ + NewItemIDs(i) listbox.AddItem AnOPCTextSting Next i 4.1.6 OPCServer Events 4.1.6.1 ServerShutDown Description The ServerShutDown event is fired when the server is planning on shutting down and wants to tell all the active clients to release any resources. The client provides this method so that the server can request that the client disconnect from the server. The client should remove all groups and items. Syntax ServerShutDown (Reason As String) Example Part Description ServerReason An optional text string provided by the server indicating the reason for the shutdown. Dim WithEvents AnOPCServer As OPCServer 29 OPC Data Access Automation Specification2.02 Dim ARealOPCServer As String Dim ARealOPCNodeName As String Set AnOPCServer = New OPCServer ‘ note we need to specify an example to facilitate creating an object that is ‘dimensioned with events ARealOPCServer = “VendorX.DataAccessCustomServer” ARealOPCNodeName = “SomeComputerNodeName” AnOPCServer.Connect(ARealOPCServer, ARealOPCNodeName) Private Sub AnOPCServer_ServerShutDown(ByRef aServerReason As String) ‘ write your client code here to let go of the server End Sub 30 OPC Data Access Automation Specification2.02 4.2 OPCBrowser Object Description The OPCBrowser object is a collection of branch or item names that exist in the server. Browsing is optional. If the server does not support browsing, CreateBrowser will not create this object. Syntax OPCBrowser Remarks The properties Filter, DataType, and AccessRights affect the collection at the time a method such as ShowLeafs is called. These properties let the client request a subset of the address space. If the user is browsing names of items to write data to, then the AccessRights property should be set to OPCWritable before calling ShowLeafs. Servers can have either a flat or hierarchical name space. When the namespace is flat, calling the method ShowLeafs fills the collection with the entire set of names in the server. Hierarchical browsing is a two step process. First, the browse position is set using a Move method, then the names are put into the collection using the Show methods. Calling ShowBranches fills the collection with the branches below the current position. Calling MoveDown with one of these branch names moves the position to that branch. Calling MoveUp moves up one level. Calling MoveToRoot moves all the way to the top level. From any position, branches and leafs can be browsed. ShowBranches and ShowLeafs should not be called from inside a For Each loop. The reason for this restriction is when in a For Each loop or a loop to Count the items, basically you would be changing the contents of the collection, and the next item has no meaning. Basically, you should not call ShowBranches and ShowLeafs while looping through the Browse object's collection. It is legal to call ShowLeafs while in a loop on some other collection. Example Dim WithEvents AnOPCServer As OPCServer Dim ARealOPCServer As String Dim ARealOPCNodeName As String Dim AnOPCServerBrowser As OPCBrowser Dim SomeName As Variant Set AnOPCServer = New OPCServer ARealOPCServer = “VendorX.DataAccessCustomServer” ARealOPCNodeName = “SomeComputerNodeName” AnOPCServer.Connect(ARealOPCServer, ARealOPCNodeName) Set browser = AnOPCServer.CreateBrowser AnOPCServerBrowser.ShowBranches AnOPCServerBrowser.MoveDown(AnOPCServerBrowser.Item(1) ) AnOPCServerBrowser.DataType = vbInteger AnOPCServerBrowser.ShowLeafs ’ 1st method for getting all names For I = 1 To AnOPCServerBrowser.Count 31 OPC Data Access Automation Specification2.02 name = AnOPCServerBrowser.Item( I ) ’ Or… name = AnOPCServerBrowser ( I ) listBox.Add name Next I ’ 2nd method for getting all names For Each name In AnOPCServerBrowser listBox.Add name Next name 4.2.1 Summary of Properties Organization Filter DataType AccessRights CurrentPosition Count Item ShowBranches ShowLeafs MoveUp MoveTo MoveToRoot GetItemID MoveDown GetAccessPaths 4.2.2 4.2.3 Summary of Methods OPCBrowser Properties 4.2.3.1 Organization Description (Read-only) Returns either OPCHierarchical or OPCFlat. Syntax Organization As Long Remarks If the organization is OPCFlat, then calling ShowBranches or any Move method has no effect. All names will be available after a single call to ShowLeafs. Example Dim TheOrganization As Long Set AnOPCServerBrowser = AnOPCServer.CreateBrowser TheOrganization = AnOPCServerBrowser.Organization 4.2.3.2 Filter Description (Read/Write) The filter that applies to ShowBranches and ShowLeafs methods. This property defaults to “” (no filtering). Servers may use this filter to narrow the list of names. Servers are recommended to support wildcards such as “*”. Syntax Filter As String See Also Appendix B – Sample String Filter Syntax Function Example VB Syntax Example (getting the property): Dim TheFilter As String 32 OPC Data Access Automation Specification2.02 TheFilter = AnOPCServerBrowser.Filter VB Syntax Example (setting the property): Dim TheFilter As String AnOPCServerBrowser.Filter = “FIC*” 4.2.3.3 DataType Description (Read/Write) The requested data type that applies to ShowLeafs methods. This property defaults to VT_EMPTY, which means that any data type is acceptable. Syntax DataType As Integer Remarks Any legal Variant type can be passed as a requested data type. The server responds with names that are compatible with this data type (may be none). This property provides the mechanism such that the client only gets the leafs that are of a certain DataType. See Also Appendix A - OPC Automation Error Handling Appendix D- Notes On Automation Data Types Example VB Syntax Example (getting the property): Dim TheDataType As Long TheDataType = AnOPCServerBrowser.DataType VB Syntax Example (setting the property): Dim TheDataType As Long AnOPCServerBrowser.DataType = vbInteger 4.2.3.4 AccessRights Description (Read/Write) The requested access rights that apply to the ShowLeafs methods. This property defaults to OPCReadable OR’d with OPCWritable (that is, everything). This property applies to the filtering, i.e. you only want the leafs with these AccessRights. Syntax AccessRights As Long Example VB Syntax Example (getting the property): Dim TheAccessRights As Long TheAccessRights = AnOPCServerBrowser.AccessRights VB Syntax Example (setting the property): Dim TheAccessRights As Long AnOPCServerBrowser.AccessRights = OPCWritable 33 OPC Data Access Automation Specification2.02 4.2.3.5 CurrentPosition Description (Read-only) Current position in the tree. This string will be “” (i.e. the "root") initially. It will always be “” if Organization is OPCFlat. Syntax CurrentPosition As String Remarks Current Position returns the absolute position and is equivalent to calling GetItemID on a branch (see also the Custom Interface Spec). Example VB Syntax Example (getting the property): Dim ACurrentPosition As String AnOPCServerBrowser.MoveDown(“level_1”) Set ACurrentPosition = AnOPCServerBrowser.CurrentPosition 4.2.3.6 Count Description (Read-only) Required property for collections. Returns the number of items in the collection. Syntax Count As Long Example VB Syntax Example (getting the property): Dim AnOPCCount As Long AnOPCCount = AnOPCServerBrowser.Count 4.2.4 OPCBrowser Methods 4.2.4.1 Item Description Required property for collections. Returns a name indexed by ItemSpecifier. The name will be a branch or leaf name, depending on previous calls to ShowBranches or ShowLeafs. Item is the default for the OPCBrowser. Syntax Item(ItemSpecifier As Variant) As String Example Part Description ItemSpecifier 1-based index into the collection AnOPCServerBrowser.ShowBranches ’ 1st method for getting all names For I = 1 To AnOPCServerBrowser.Count SomeName = AnOPCServerBrowser.Item( I ) 34 OPC Data Access Automation Specification2.02 listBox.Add SomeName Next I ’ 2nd method for getting all names For I = 1 To AnOPCServerBrowser.Count SomeName = AnOPCServerBrowser( I ) listBox.Add SomeName Next I ’ 3rd method for getting all names For Each SomeName In browser listBox.Add SomeName Next SomeName 4.2.4.2 ShowBranches Description Fills the collection with names of the branches at the current browse position. Syntax ShowBranches() Example AnOPCServerBrowser.ShowBranches 4.2.4.3 ShowLeafs Description Fills the collection with the names of the leafs at the current browse position. Default for Flat is FALSE. Syntax ShowLeafs(Optional Flat As Variant) Settings Part Description Flat Defines what the collection should contain. The Settings for Flat are: Settings Description True the collection is filled with all leafs at the current browse position, as well as all the leafs that are below the current browse position. Basically we are treated from the current position on down as a flat name space. False the collection is filled with all leafs at the current browse position 35 OPC Data Access Automation Specification2.02 Remarks The names of leafs in the collection should match the filter criteria defined by DataType, AccessRights, and Filter. Default for Flat is FALSE. Example AnOPCServerBrowser.MoveDown (“Floor1_Mixing”) AnOPCServerBrowser.ShowLeafs 4.2.4.4 MoveUp Description Move up one level in the tree. Syntax MoveUp() Example AnOPCServerBrowser.MoveUp 4.2.4.5 MoveToRoot Description Move up to the first level in the tree. Syntax MoveToRoot() Example AnOPCServerBrowser.MoveToRoot 4.2.4.6 MoveDown Description Move down into this branch. Syntax MoveDown(Branch As String) Example AnOPCServerBrowser.MoveDown (“Floor1_Mixing”) 4.2.4.7 MoveTo Description Move to an absolute position. Syntax MoveTo(Branches() As String) Remarks Example Part Description Branches Branches are an array of branch names from the root to a particular position in the tree. This method is equivalent to calling MoveToRoot, followed by MoveDown for each branch name in the array. Dim branches(3) As String 36 OPC Data Access Automation Specification2.02 AnOPCServerBrowser.MoveToRoot branches(1) = “node” branches(2) = “device” branches(3) = “group” browser.MoveTo branches Set ACurrentPosition = AnOPCServerBrowser.CurrentPosition ‘ACurrentPosition is now “node.device.group” 4.2.4.8 GetItemID Description Given a name, returns a valid ItemID that can be passed to OPCItems Add method. Syntax GetItemID(Leaf As String) As String Part Description Leaf The name of a BRANCH or LEAF at the current level. Remarks The server converts the name to an ItemID based on the current “position” of the browser. It will not correctly translate a name if MoveUp, MoveDown, etc. has been called since the name was obtained. Example AnOPCServerBrowser.ShowLeafs For I = 1 To AnOPCServerBrowser.Count Set AnOPCItemID = AnOPCServerBrowser.GetItemID(I) Next I ‘ or AnOPCServerBrowser.MoveDown “Mixing” Set AnOPCItemID = AnOPCServerBrowser.GetItemID(“FIC101.PV”) 4.2.4.9 GetAccessPaths Description Returns the strings that are legal AccessPaths for this ItemID. May be Null if there are no AccessPaths for this ItemID or the server does not support them. Syntax GetAccessPaths(ItemID As String) As Variant Part Description 37 OPC Data Access Automation Specification2.02 ItemID Remarks Example Fully Qualified ItemID AccessPath is the “how” for the server to get the data specified by the ItemID (the what). The client uses this function to identify the possible access paths for the specified ItemID. AnOPCServerBrowser.ShowLeafs For I = 1 To AnOPCServerBrowser.Count Set AnAccessPath = AnOPCServerBrowser.GetAccessPaths(“FIC101.PV) Next I ‘ or AnOPCServerBrowser.MoveDown “Mixing” Set AnAccessPath = AnOPCServerBrowser.GetAccessPaths(“FIC101.PV) 38 OPC Data Access Automation Specification2.02 4.3 OPCGroups Object Description OPCGroups is a collection of OPCGroup objects, and the methods that create, remove, and manage them. This object also has properties for OPCGroup defaults. When OPCGroups are added, the DefaultGroupXXXX properties set its initial state. The defaults can be changed to add OPCGroups with different initial states. Changing the defaults does not affect groups that have already been created. Once an OPCGroup is added, its properties can be modified. This reduces the number of parameters required to call the Add method. Syntax OPCGroups 4.3.1 Summary of Properties Parent DefaultGroupIsActive DefaultGroupUpdateRate DefaultGroupDeadband Count DefaultGroupLocaleID DefaultGroupTimeBias Add RemoveAll GetOPCGroup ConnectPublicGroup 4.3.2 Summary of Methods Item Remove RemovePublicGroup 4.3.3 Summary of Events GlobalDataChange Example Syntax Base The following sample code is necessary for the subsequent Visual Basic Examples to be operational. This code is referred to as OPCGroupsObjectBase. Dim WithEvents AnOPCServer As OPCServer Dim ARealOPCServer As String Dim ARealOPCNodeName As String Dim AnOPCServerBrowser As OPCBrowser Dim MyGroups As OPCGroups Dim DefaultGroupUpdateRate As Long Dim OneGroup As OPCGroup Dim AnOPCItemCollection As OPCItems Dim AnOPCItem As OPCItem Dim ClientHandles(100) As Long Dim AnOPCItemIDs(100) As String 39 OPC Data Access Automation Specification2.02 Dim AnOPCItemServerHandles() As Long Dim AnOPCItemServerErrors() As Long Set AnOPCServer = New OPCServer ARealOPCServer = “VendorX.DataAccessCustomServer” ARealOPCNodeName = “SomeComputerNodeName” AnOPCServer.Connect(ARealOPCServer, ARealOPCNodeName) Set MyGroups = AnOPCServer.OPCGroups MyGroups.DefaultGroupIsActive = True Set OneGroup = MyGroups.Add( “AnOPCGroupName” ) Set AnOPCItemCollection = OneGroup.OPCItems 4.3.4 OPCGroups Properties 4.3.4.1 Parent Description (Read-only) Returns reference to the parent OPCServer object. Syntax Parent As OPCServer 4.3.4.2 DefaultGroupIsActive Description (Read/Write) This property provides the default active state for OPCGroups created using Groups.Add. Syntax DefaultGroupIsActive As Boolean Remarks This property defaults to True. Example VB Syntax Example (getting the property): Dim DefaultGroupIsActive As Boolean DefaultGroupIsActive = MyGroups.DefaultGroupIsActive VB Syntax Example (setting the property): MyGroups.DefaultGroupIsActive = FALSE 4.3.4.3 DefaultGroupUpdateRate Description (Read/Write) This property provides the default update rate (in milliseconds) for OPCGroups created using Groups.Add. This property defaults to 1000 milliseconds (1 second). Syntax DefaultGroupUpdateRate As Long Example VB Syntax Example (getting the property): 40 OPC Data Access Automation Specification2.02 Dim DefaultGroupUpdateRate As Long DefaultGroupUpdateRate = MyGroups.DefaultGroupUpdateRate VB Syntax Example (setting the property): MyGroups.DefaultGroupUpdateRate = 250 4.3.4.4 DefaultGroupDeadband Description (Read/Write) This property provides the default deadband for OPCGroups created using Groups.Add. A deadband is expressed as percent of full scale (legal values 0 to 100). Syntax DefaultGroupDeadband As Single Remarks This property defaults to 0. Error would be generated if value > 100 or less than 0. Example VB Syntax Example (getting the property): Dim DefaultGroupDeadband As Single DefaultGroupDeadband = MyGroups.DefaultGroupDeadband VB Syntax Example (setting the property): MyGroups.DefaultGroupDeadband = 10 4.3.4.5 DefaultGroupLocaleID Description (Read/Write) This property provides the default locale for OPCGroups created using Groups.Add. Syntax DefaultGroupLocaleID As Long Remarks This property defaults to the Servers LocaleID.. Example VB Syntax Example (getting the property): Dim DefaultGroupLocaleID As Long DefaultGroupLocaleID = MyGroups.DefaultGroupLocaleID VB Syntax Example (setting the property): MyGroups.DefaultGroupLocaleID = ConvertLocaleIdStringToLocaleIdLong (“English”) 4.3.4.6 DefaultGroupTimeBias Description (Read/Write) This property provides the default time bias for OPCGroups created using Groups.Add. Syntax DefaultGroupTimeBias As Long Remarks This property defaults to 0 minutes. Example VB Syntax Example (getting the property): Dim DefaultGroupTimeBias As Long 41 OPC Data Access Automation Specification2.02 DefaultGroupTimeBias = MyGroups.DefaultGroupTimeBias VB Syntax Example (setting the property): MyGroups.DefaultGroupTimeBias = 60 4.3.4.7 Count Description (Read-only) Required property for collections. Syntax Count As Long Example VB Syntax Example : For index = 1 to MyGroups.Count ‘ some code here Next index 4.3.5 OPCGroups Methods 4.3.5.1 Item Description Returns an OPCGroup by ItemSpecifier. ItemSpecifier is the name or 1-based index into the collection. Use GetOPCGroup to reference by ServerHandle. Item is the default method for OPCGroups. Syntax Item(ItemSpecifier As Variant) As OPCGroup Example VB Syntax Example: Dim AnOPCGroup As OPCGroup Set AnOPCGroup = MyGroups.Item(3) ‘Or Set AnOPCGroup = MyGroups(“Group3”) 4.3.5.2 Add Description Creates a new OPCGroup object and adds it to the collection. The properties of this new group are determined by the current defaults in the OPCServer object. After a group is added, its properties can also be modified. Syntax Add(Optional Name As Variant) As OPCGroup Part Description Name Name of the group. The name must be unique among the other groups created by this client. If no name is provided, The server-generated name will also be unique relative to any existing groups. 42 OPC Data Access Automation Specification2.02 Remarks If the optional name is not specified, the server generates a unique name. This method will fail if a name is specified but it is not unique. A failure in this case results in the OPCGroup object not being created, and Visual Basic will generate an error when attempting to use the object that has not been set. Refer to Appendix A - OPC Automation Error Handling for information on OPC Automation errors and Exceptions. Example MyGroups.DefaultGroupIsActive = True Set OneGroup = MyGroups.Add( “AnOPCGroupName” ) 4.3.5.3 GetOPCGroup Description Returns an OPCGroup by ItemSpecifier. Syntax GetOPCGroup (ItemSpecifier As Variant) As OPCGroup Part Description ItemSpecifier ItemSpecifier is either the OPCGroup’s ServerHandle, or the name of an OPCGroup. Use Item to reference by index. Example ‘ If “AnOPCGroupName” has already been Added Set OneGroup = MyGroups.GetOPCGroup( “AnOPCGroupName” ) 4.3.5.4 Remove Description Removes an OPCGroup by Key. Syntax Remove(ItemSpecifier As Variant) Remarks Example Part Description ItemSpecifier ItemSpecifier is either the OPCGroup’s ServerHandle, or the name of an OPCGroup. Use Item to reference by index. This method will fail if the group is a public group. Refer to Appendix A - OPC Automation Error Handling for information on OPC Automation Errors and Exceptions. Set OneGroup = MyGroups.Add( “AnOPCGroupName” ) ‘ some more code here MyGroups.Remove( “AnOPCGroupName” ) ‘or Set OneGroup = MyGroups.Add( “AnOPCGroupName” ) ‘ some more code here MyGroups.Remove(OneGroup.ServerHandle ) 43 OPC Data Access Automation Specification2.02 4.3.5.5 RemoveAll Description Removes all current OPCGroup and OPCItem objects to prepare for server shutdown. Syntax RemoveAll() Remarks This is designed to make thorough sub-object cleanup much easier for clients to ensure all objects are released when the Server object is released. It is equivalent to calling Remove on all remaining OPCItem and OPCGroup objects. OPCBrowser objects are not sub-objects of the server, and they are not removed by this method. Example Set OneGroup = MyGroups.Add( “AnOPCGroupName” ) Set OneGroup = MyGroups.Add( “AnOPCGroupName1” ) Set OneGroup = MyGroups.Add( “AnOPCGroupName2” ) ‘ some more code here MyGroups.RemoveAll 4.3.5.6 ConnectPublicGroup Description Public Groups are pre-existing groups in a server. These groups can be connected rather than added.. Refer to Appendix A - OPC Automation Error Handling for information on OPC Automation errors and Exceptions. Syntax ConnectPublicGroup (Name As String) As OPCGroup Part Description Name Name of group to be connected. Remarks This method will fail if the server does not support public groups or the name is not valid Refer to Appendix A - OPC Automation Error Handling for information on OPC Automation errors and Exceptions Example Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCServerDefinedPublicGroup”” ) 4.3.5.7 RemovePublicGroup Description Removes the OPCGroup specified by ItemSpecifier. Syntax RemovePublicGroup (ItemSpecifier As Variant) Remarks Part Description ItemSpecifier The ServerHandle returned by ConnectPublicGroup, or the name of a Public OPCGroup. This method will fail if the server does not support public groups, or if the group has not been connected to via ConnectPublicGroup. 44 OPC Data Access Automation Specification2.02 Refer to Appendix A - OPC Automation Error Handling for information on OPC Automation errors and Exceptions Example Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here MyGroups.RemovePublicGroup ( “AnOPCGroupName” ) ‘or Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here MyGroups.RemovePublicGroup (OneGroup.ServerHandle ) 4.3.6 OPCGroups Events 4.3.6.1 GlobalDataChange Description The GlobalDataChangeevent is an event to facilitate one event handler being implemented to receive and process data changes across multiple groups. Syntax GlobalDataChange (TransactionID As Long, GroupHandle As Long, NumItems As Long, ClientHandles() As Long, ItemValues() As Variant, Qualities() As Long, TimeStamps() As Date) Remarks Part Description TransactionID The client specified transaction ID. A non-0 value for this indicates that this call has been generated as a result of an AsyncRefresh. A value of 0 indicates that this call has been generated as a result of normal subscription processing. GroupHandle ClientHandle of the OPCGroup Object the changed data corresponds to. NumItems The number of items returned ClientHandles Array of client item handles for the items ItemValues Array of values. Qualities Array of Qualities for each item's value. TimeStamps Array of UTC TimeStamps for each item's value NOTE – it is recommended that the event OnDataChange on the OPCGroup object be used normally. This event has been provided to facilitate one event handler being set up to process data changes for multiple OPCGroup objects. Normally, your application has an individual event handler for each group to receive and process the data changes. This allows you to have one event handler, and then 45 OPC Data Access Automation Specification2.02 using the GroupHandle, know which Group the event has been fired on behalf of. This event will be invoked for each OPCGroup object that contains an item, whose value or state of the value has changed since the last time this event, was fired. The individual event on the OPCGroup object is also fired as well. Your application, when using both event handlers will receive the data value twice, once for the individual group event, and once for the AllGroupsDataChange Event. Example Dim WithEvents AnOPCGroupCollection As OPCGroups Private Sub AnOPCGroupCollection_GlobalDataChange (TransactionID As Long, GroupHandle As Long, MasterQuality As Long, MasterError As Long, NumItems As Long, ClientHandles() As Long, ItemValues() As Variant, Qualities() As Long, TimeStamps() As Date) ‘ write your client code here to process the data change values End Sub 46 OPC Data Access Automation Specification2.02 4.4 OPCGroup Object Description The OPC Groups provide a way for clients to organize data. For example, the group might represent items in a particular operator display or report. Data can be read and written. Exception based connections can also be created between the client and the items in the group and can be enabled and disabled as needed. An OPC client can configure the rate that an OPC server should provide the data changes to the OPC client. Syntax OPCGroup 4.4.1 Summary of Properties Parent Name IsPublic IsActive ServerHandle IsSubscribed LocaleID ClientHandle TimeBias DeadBand UpdateRate OPCItems SyncRead SyncWrite AsyncRead AsyncWrite AsyncRefresh AsyncCancel AsyncReadComplete AsyncWriteComplete 4.4.2 4.4.3 Summary of Methods Summary of Events DataChange AsyncCancelComplete Example Syntax Base The following sample code is necessary for the subsequent Visual Basic Examples to be operational. . This code is referred to as OPCGroupObjectBase. Dim WithEvents AnOPCServer As OPCServer Dim ARealOPCServer As String Dim ARealOPCNodeName As String Dim AnOPCServerBrowser As OPCBrowser Dim MyGroups As OPCGroups Dim DefaultGroupUpdateRate As Long Dim WithEvents OneGroup As OPCGroup Dim AnOPCItemCollection As OPCItems Dim AnOPCItem As OPCItem Dim ClientHandles(100) As Long Dim AnOPCItemIDs(100) As String 47 OPC Data Access Automation Specification2.02 Dim AnOPCItemServerHandles() As Long Dim AnOPCItemServerErrors() As Long Set AnOPCServer = New OPCServer ARealOPCServer = “VendorX.DataAccessCustomServer” ARealOPCNodeName = “SomeComputerNodeName” AnOPCServer.Connect(ARealOPCServer, ARealOPCNodeName) Set MyGroups = AnOPCServer.OPCGroups MyGroups.DefaultGroupIsActive = True Set OneGroup = MyGroups.Add( “AnOPCGroupName” ) Set AnOPCItemCollection = OneGroup.OPCItems For x = 1 To AddItemCount ClientHandles(x) =x+1 AnOPCItemID(x) = “Register_” & x Next x AnOPCItemCollection.AddItems AddItemCount, AnOPCItemIDs, AnOPCItemServerHandles, AnOPCItemServerErrors 4.4.4 OPCGroup Properties 4.4.4.1 Parent Description (Read-only) Returns reference to the parent OPCServer object. Syntax Parent As OPCServer 4.4.4.2 Name Description (Read/Write) The name given to this group. Syntax Name As String Part Description Name Name of the group. The name must be a unique group name, with respect to the naming of other groups created by this client. 48 OPC Data Access Automation Specification2.02 Remarks Example Naming a group is optional. This property allows the user to specify a name, therefore a unique name must be provided when setting the value for this property. The server will generate a unique name for the group, if no name is specified, on the Add method of the OPCGroups object. VB Syntax Example (getting the property): Dim CurrentValue As String Set OneGroup = MyGroups.Add( “AnOPCGroupName” ) CurrentValue = OneGroup.Name VB Syntax Example (setting the property): Set OneGroup = MyGroups.Add( “AnOPCGroupName” ) OneGroup.Name = “aName” 4.4.4.3 IsPublic Description (Read-only) Returns True if this group is a public group, otherwise False. Syntax IsPublic As Boolean Example Dim CurrentValue As Boolean Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here Set CurrentValue = OneGroup.IsPublic ‘ to get the value 4.4.4.4 IsActive Description (Read/Write) This property controls the active state of the group. A group that is active acquires data. An inactive group typically does not continue data acquisition except as required for read/writes. Syntax IsActive As Boolean Remarks Default value for this property is the value from the OPCGroups corresponding default value at time of the Add(); Example VB Syntax Example (getting the property): Dim CurrentValue As Boolean Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here Set CurrentValue = OneGroup.IsActive ‘ to get the value VB Syntax Example (setting the property): 49 OPC Data Access Automation Specification2.02 Dim CurrentValue As Boolean Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here OneGroup.IsActive = True 4.4.4.5 IsSubscribed Description (Read/Write) This property controls asynchronous notifications to the group. A group that is subscribed receives data changes from the server. Syntax IsSubscribed As Boolean Remarks Default value for this property is the value from the OPCGroups corresponding default value at time of the Add(); Example VB Syntax Example (getting the property): Dim CurrentValue As Boolean Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here Set CurrentValue = OneGroup.IsSubscribed ‘ to get the value VB Syntax Example (setting the property): Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here OneGroup.IsSubscribed = True ‘ to set the value 4.4.4.6 ClientHandle Description (Read/Write) A Long value associated with the group. Its purpose is for the client to quickly locate the destination of data. The handle is typically an index, etc. This handle will be returned to the client along with data or status. Syntax ClientHandle As Long Example VB Syntax Example (getting the property): Dim CurrentValue As Long Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here 50 OPC Data Access Automation Specification2.02 Set CurrentValue = OneGroup.ClientHandle ‘ to get the value VB Syntax Example (setting the property): Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here OneGroup.ClientHandle = 1975 ‘ to set the value 4.4.4.7 ServerHandle Description (Read-only) The server assigned handle for the group. The ServerHandle is a Long that uniquely identifies this group. The client must supply this handle to some of the methods that operate on OPCGroup objects (such as OPCGroups.Remove). Syntax ServerHandle As Long Example VB Syntax Example (getting the property): Dim CurrentValue As Long Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here Set CurrentValue = OneGroup.ServerHandle ‘ to get the value 4.4.4.8 LocaleID Description (Read/Write) This property identifies the locale, which may be used to localize strings returned from the server. This property’s default depends on the value set in the OPCGroups Collection.. Syntax LocaleID As Long Example VB Syntax Example (getting the property): Dim CurrentValue As Long Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here Set CurrentValue = OneGroup.LocaleID VB Syntax Example (setting the property): Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here OneGroup.LocaleID = StringToLocaleID(“English”) 51 OPC Data Access Automation Specification2.02 4.4.4.9 TimeBias Description (Read/Write). This property provides the information needed to convert the time stamp on the data back to the local time of the device. Syntax TimeBias As Long Example VB Syntax Example (getting the property): Dim CurrentValue As Long Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here Set CurrentValue = OneGroup.TimeBias VB Syntax Example (setting the property): Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here OneGroup.TimeBias = 100 4.4.4.10 DeadBand Description (Read/Write) A deadband is expressed as percent of full scale (legal values 0 to 100). This property’s default depends on the value set in the OPCGroups Collection. Syntax DeadBand As Single Example VB Syntax Example (getting the property): Dim CurrentValue As Single Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here Set CurrentValue = OneGroup.DeadBand VB Syntax Example (setting the property): Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here OneGroup.DeadBand = 5 52 OPC Data Access Automation Specification2.02 4.4.4.11 UpdateRate Description (Read/Write) The fastest rate at which data change events may be fired. A slow process might cause data changes to fire at less than this rate, but they will never exceed this rate. Rate is in milliseconds. This property’s default depends on the value set in the OPCGroups Collection. Assigning a value to this property is a “request” for a new update rate. The server may not support that rate, so reading the property may result in a different rate (the server will use the closest rate it does support). Syntax UpdateRate As Long Example VB Syntax Example (getting the property): Dim CurrentValue As Long Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here DefaultGroupUpdateRate = OneGroup.UpdateRate VB Syntax Example (setting the property): Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here OneGroup.UpdateRate = 50 4.4.4.12 OPCItems Description A collection of OPCItem objects. This is the default property of the OPCGroup object. Syntax OPCItems As OPCItems Example VB Syntax Example (getting the property): Dim AnOPCItemCollection As OPCItems Set MyGroups = AnOPCServer.OPCGroups Set OneGroup = MyGroups.ConnectPublicGroup ( “AnOPCGroupName” ) ‘ some more code here Set AnOPCItemCollection = OneGroup.OPCItems 4.4.5 OPCGroup Methods 4.4.5.1 SyncRead Description This function reads the value, quality and timestamp information for one or more items in a group. Syntax SyncRead(Source As Integer, NumItems As Long, ServerHandles() As Long, ByRef Values() As Variant, ByRef Errors() As Long, Optional ByRef Qualities As Var...

Data Access Automation Interface Standard

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