Rate = ServerGroups.DefaultGroupUpdateRate
    GetDefaultGroupUpdateRate = True
    GoTo SkipOPCGetDefaultUpdateRateError
    
ShowOPCGetDefaultUpdateRateError:
    Call DisplayOPC_COM_ErrorValue("GetDefaultGroupUpdateRate", Err.Number)
    GetDefaultGroupUpdateRate = False
    
SkipOPCGetDefaultUpdateRateError:
End Function


' The name say it all, gets the default DeadBand from the
' ServerGroups collection object.
'
Function GetDefaultGroupDeadBand(ByRef DeadBand As Single)
    'Set error handling for OPC Function
    On Error GoTo ShowOPCGetDefaultGroupDeadBandError
    
    DeadBand = ServerGroups.DefaultGroupDeadband
    GetDefaultGroupDeadBand = True
    GoTo SkipOPCGetDefaultGroupDeadBandError
    
ShowOPCGetDefaultGroupDeadBandError:
    Call DisplayOPC_COM_ErrorValue("GetDefaultGroupDeadBand", Err.Number)
    GetDefaultGroupDeadBand = False
    
SkipOPCGetDefaultGroupDeadBandError:
End Function


' This sub handles adding the group to the OPC server and
' establishing the group interface.  When adding a group you
' can preset some of the group parameters using the properties
' '.DefaultGroupIsActive' and '.DefaultGroupDeadband'.  Set these
' before adding the group. Once the group has been successfully
' added you can change these same settings along with the group
' update rate on the fly using the properties on the resulting
' OPCGroupClass object.
' The GroupName parameter is the name your would like to use for
' the new group to be added.  This paramter can be left blank.
' When you leave the group name blank you are telling the OPC server
' that is should generate a group name for us.  See the SetDefault
' functions above for details on the UpdateRate, DeadBand, and active
' state of the group.
'
' The GroupKey is string that will be returned to the VB application.
' This string can be used as a key for this group in a collection.
'
Function AddOPCGroup(GroupName As String, UpdateRate As Long, DeadBand As Single, ActiveState As Boolean, ByRef GroupKey As String)
    'Set error handling for OPC Function
    On Error GoTo ShowOPCGroupAddError
    
    ' Create an new instance of the OPCGroupClass
    Dim ConnectedGroup As New OPCGroupClass
    Dim NewGroup As OPCGroup
    Dim GroupNum As Integer
              
    ' Establish the initial default conditions for new groups added to this
    ' server.
    SetDefaultGroupIsActive (ActiveState)
    SetDefaultGroupUpdateRate (UpdateRate)
    SetDefaultGroupDeadBand (DeadBand)

    ' Normally you can name an OPC group yourself but
    ' you also have the option of allowing the OPC Server
    ' to provide you with a unique group name automatically.
    ' To do this simply leave the GroupName empty.
    ' This blank group name is then passed to the OPC
    ' server which will recognize this as a automatic
    ' group name.  The server will return the name it
    ' generates as part of the Automation Interface's
    ' OPCGroup object.
    
    Set NewGroup = ServerGroups.Add(GroupName)
    
    
    ' If the GroupName was passed in as blank then get the group
    ' name that the OPC Server has automatically generated.
    If GroupName = "" Then
        GroupName = NewGroup.Name
    End If
    
    ' The FindNextGroupNumber handles getting a unique group number
    ' if you continue to add groups to your OPCServerClass object
    ' this function simply returns the next group number.  If you
    ' delete a group that was previously added this function will
    ' attempt to find the deleted group numbers and use them first.
    ' This prevents the group index numbers from just continuing to
    ' increment.
    GroupNum = FindNextGroupNumber
    
    ' Once the next group number is found a unique group key is
    ' developed.  This key can be used in your application to manage
    ' access to this group.  One example might be to use the GroupKey
    ' returned here as a key within a TreeView of ListView control.
    ' As you can see here the group key is comprise of the group
    ' index specifically for this group and on the server index.
    ' By combining these two index numbers in one key we can be
    ' resonably sure that the group key will be unique across
    ' multiple OPC server groups.
    GroupKey = "Group" + Str(GroupNum) + Str(OPCServerIndex)
    
    ' On the outside chance the OPC server didn't generated a group name
    ' we can create one from the Groupkey.
    If GroupName = "" Then
        GroupName = GroupKey
    End If
   
    ' This sets the basic properties of the OPCGroupClass object
    ConnectedGroup.SetOPCGroup NewGroup, GroupName, GroupKey, GroupNum
    
    ' Although the OPCGroups (ServerGroups) object is already a
    ' collection we need to have our own OPCGGroupClass object wrapper
    ' to contain the properties and events for each group we intend
    ' to add to the server.  This means that we must keep the
    ' ServerGroups collection and the OPCServerGroups collection
    ' in sync.
    With OPCServerGroups
        .Add ConnectedGroup, GroupKey
    End With
        
    AddOPCGroup = True
    GoTo SkipAddGroupError

ShowOPCGroupAddError:
    Call DisplayOPC_COM_ErrorValue("Add Group", Err.Number)
    AddOPCGroup = False
    
SkipAddGroupError:
End Function


' This function attempts to keep the Group index number
' from continuosly growing by finding a group number that
' may have been deleted and returning those first before
' going to the next group index number. The end result of
' this function it that the group number will never grow
' beyond actual number of groups.
'
Private Function FindNextGroupNumber()
    ' In this function an error state means that a vacant
    ' group number has been found.
    On Error GoTo FoundNextGroupNumber
    
    Dim i As Integer
    Dim GroupNum As Integer
    
    GroupNum = 1
    
    With OPCServerGroups
        ' This loop tries to access each item in the OPCServerGroups
        ' collection by it's Key.  If an item can not be pulled from the
        ' collection that means the group had been deleted and it's
        ' group number is available.
        For i = 1 To .Count
            GroupNum = i
            .Item ("Group" + Str(i) + Str(OPCServerIndex))
        Next i
        
        ' If we get here all of the group numbers in the collection
        ' exist and a next available group number should be returned.
        If .Count <> 0 Then
            FindNextGroupNumber = i
        Else
            FindNextGroupNumber = 1 ' No count return the first 1
        End If
    End With
    
    GoTo NewGroup
    
FoundNextGroupNumber:
    ' If we get here a group number could not be found in the
    ' OPCServerGroups collection which means that it has been deleted
    ' and is available for a new group addition.
    FindNextGroupNumber = GroupNum
    
NewGroup:
End Function


' This sub handles removing a group from the OPC server.  The group
' is removed from the ServerGroups object which is the collection
' managed by the Automation Interface.  Then the group is removed from
' the OPCServerGroups collection which is managed by the OPCServerClass
'
Function RemoveOPCGroup(GroupKey As String)
    'Set error handling for OPC Function
    On Error GoTo ShowOPCGroupRemoveError
      
    Dim OPCGroupCls As OPCGroupClass
    Set OPCGroupCls = OPCServerGroups.Item(GroupKey)
    Dim GroupName As String
    GroupName = OPCGroupCls.GetGroupName
      
    ' First the group is removed from the actual group collection managed by
    ' the automation interface if it is successful then remove the tiem from the
    ' OPCServerGroups collection
    ServerGroups.Remove GroupName
    
    ' Now we remove it from the OPCServerGroups collection
    ' to allow any final processing on the group to be done
    OPCServerGroups.Remove GroupKey
        
    RemoveOPCGroup = True
    GoTo SkipRemoveGroupError

ShowOPCGroupRemoveError:
    Call DisplayOPC_COM_ErrorValue("Remove Group", Err.Number)
    RemoveOPCGroup = False
    
SkipRemoveGroupError:
End Function


' The OPCServerClass object has the ability to generate an event when
' an OPC server is shutting down.   When an OPC server supports the
' OPC 2.0 data access specification, it has the option of issuing a
' ServerShutDown event to any of it's attached clients.  In the case
' of a VB application the OPCServer oject will signal the
' ServerShutDown event.  This event is handled here in the OPCServerClass
' object.  If this event fires, the ServerShuttingDown event of the
' OPCServerClass object will be fired.  A VB application has the option of
' hooking the ServerShuttingDown event to be informed when the OPC
' connection is going to be lost.
'
Private Sub OPCServerObj_ServerShutDown(ByVal Reason As String)
    ' If we receive a server shut down message we need to release everthing and remove the server
    ' connection.
    RaiseEvent ServerShuttingDown(OPCServerKey)
End Sub


' Create the new OPCServer object when the OPCServerClass object is
' instantiated.
'
Private Sub Class_Initialize()
    Set OPCServerObj = New OPCServer
End Sub


' When the OPCServerClass object is deleted this function will cleanup
' the OPC connection by releasing the groups and items.  While this function
' will clean up the groups and items that may have been attached to this
' OPCServerClass object you will still need to call DisconnectOPCServer
' in your VB application on this object to properly release the OPC Server
' from the Automation Interface.
'
Private Sub Class_Terminate()
    
    ' Normally you should remove all groups and their items from the server
    ' before you remove the server object.  However the OPCGroups collection
    ' object supports a RemoveAll method that will remove all items from
    ' the groups and all groups from the server.
    If Not ServerGroups Is Nothing Then
        If ServerGroups.Count <> 0 Then
            ServerGroups.RemoveAll
        End If
    End If
    
    ' We still need to remove the OPCServerGroups collection that contains
    ' the OPCGroupClasss objects
    If OPCServerGroups.Count <> 0 Then
        Dim i As Integer
        Dim a As Integer
        a = OPCServerGroups.Count
        For i = 1 To OPCServerGroups.Count
            With OPCServerGroups
            .Remove (a)
            a = a - 1
            End With
        Next i
    End If
    
    ' Release the OPCServerGroups collection
    Set OPCServerGroups = Nothing
    
End Sub


' Handles displaying any OPC/COM/VB errors that are caught by the exception handler
Sub DisplayOPC_COM_ErrorValue(OPC_Function As String, ErrorCode As Long)
    Dim Response
    Dim ErrorDisplay As String
    ErrorDisplay = "The OPC function '" + OPC_Function + "' has returned an error of " + Str(ErrorCode) + " or Hex 0x" + Hex(ErrorCode)
    Response = MsgBox(ErrorDisplay, vbOKOnly, "OPC Function Error")
End Sub