Opc data Access Automation Specification

4.4.5.4

 

AsyncWrite 

Description 

Write one or more items in a group. The results are returned via the AsyncWriteComplete event 

associated with the OPCGroup object. 

Syntax 

AsyncWrite(NumItems As Long, ServerHandles() As Long, Values() As Variant, ByRef Errors() 

As Long, TransactionID As Long, ByRef CancelID As Long) 

 

Part Description 

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OPC Data Access Automation Specification2.02 

NumItems 

The number of items to be written. 

ServerHandles 

Array of server item handles for the items to be written. 

Values 

Array of values. 

Errors 

Array of Long’s indicating the status of the individual items to be 

written.  

TransactionID 

The client specified transaction ID. This is included in the 

‘completion’ information provided in the Corresponding Event. 

CancelID 

A Server generated transaction ID. This is provided to enable the 

client to cancel the “transaction”. 

 

Remarks 

The AsyncWrite requires the OPCGroup object to have been dimensioned with events (Dim 

WithEvents xxx As OPCGroup) in order for the results of the AsyncWrite operation to be returned to 

the automation client application.  The AsyncWriteComplete event associated with the OPCGroup 

object will be fired (called) by the automation server with the results of the AsyncWrite operation.  

See Also 

IOPCAsyncIO2::Write from the OPC Data Access Custom Interface Specification 

Example Private 

Sub 

AsyncWriteButton_Click() 

Dim NumItems As Long  

Dim ServerIndex As Long  

Dim ServerHandles(10) As Long  

Dim Values() As Variant  

Dim Errors() As Long  

Dim ClientTransactionID As Long  

Dim ServerTransactionID As Long 

NumItems = 10 

For ServerIndex = 1 to NumItems 

ClientTransactionID = 1957

 

‘ set up which items to be write 

ServerHandles(ServerIndex) = AnOPCItemServerHandles(ServerIndex) 

Values(ServerIndex) = ServerIndex * 2  ‘any random value for this example would suffice 

Next ServerIndex 

OneGroup.AsyncWrite NumItems, ServerHandles, Values, Errors, ClientTransactionID , 

ServerTransactionID 

End Sub 

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OPC Data Access Automation Specification2.02