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WriteValue works where WriteMultiple does not

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27 Mar 2014 16:50 #1789 by support
I am glad you made it work - even before I could reply.

FYI, the "Write" methods are all implemented on top of "WriteMultiple", and the "WriteValue" methods are all implemented on top of "WriteMultipleValues" methods. So, if e.g. "WriteMultiple" works, and "Write" does not, the difference must be somehow related to the arguments being passed in.

In OPC-UA, the spec is more strict about the type of value that goes to the Write service of the OPC-UA server, compared to OPC Data Access. As you can see (and the doc describes), it can get problematic at times. Basically, you either have to properly specify the type with each value written (or have the value already in the precise type), OR we (on the client side) will allow you to omit the type, at the cost of performance.

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27 Mar 2014 13:00 #1788 by cdunlap
I have gone back to using the WriteMultiple function, but not including the Typecode in the parameters. This seems to work just as well as the WriteMultipleValues function.

As I was reading the Concepts document, I discovered that, if a TypeCode is not supplied, WriteMultiple will actually do a read of the item to determine the type. I was doing this with my code and the setting the TypeCode to the return item type.

It seems to be working fine at the moment.

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27 Mar 2014 12:41 #1787 by cdunlap
Hi,

I apologize for not giving the exception earlier. It gives a BadTypeMismatch ({*** Failure -2139881472 (0x80740000): OPC-UA service result - An error specific to OPC-UA service occurred.}) which is even more strange since I get the type from it before trying to write.

When using the WriteValue, where I don't specify the type, it will write.

I am using TOP Server 5.9.170.0 - I checked the release notes for anything particular to that driver, but I didn't see anything about a bug with

Thank you again.

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27 Mar 2014 06:06 #1786 by support
Hello,
can you please give following more detail:
  • What is the version of the TOP Server (the full, precise version number).
  • Do you get any error, and if so, what error precisely, when you say that it does not work? Note that you need to check the output of the WriteMultiple one by one, it does not throw exceptions for this.
Thank you

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26 Mar 2014 21:16 - 27 Mar 2014 06:01 #1785 by cdunlap
Hi,

I have been using WriteMultiple to write to different PLCs and it works for all except one special case, a SLC 500 and an integer tag. I have included my code that works for all of the other scenarios.

Here is my WriteMultiple function and how I call it….
Calling routine:
       DimsServerName As String 
        DimsTagRead(0) As String 
        DimsTagWrite(0) As String 
        DimoWriteValues(0) As Object 
        DimoTypeCode(0) As TypeCode 
        DimbResult As Boolean= False
    bResult = OPC_UA_WriteMultipleItems(“192.168.2.115:49380”, “SLC500.SLC500.N7:0”,  "nsu=TOP Server;ns=2;s=", “123”, oTypeCode)

End of calling routine
    FunctionOPC_UA_WriteMultipleItems(ByValsServerName As String, _
                                       ByValTags() As String, _
                                       ByValsServerType As String, _
                                       ByValoValues() As Object, _
                                       ByValoTypeCode() As TypeCode) As Boolean
        DimReadValues() As ValueResult= Nothing
        'Read tags to get varibale types 
        OPC_UA_ReadMultipleItems(sServerName, Tags, sServerType, ReadValues)
        DimI As Integer 
        DimeasyUAClient1 = New EasyUAClient()
        'create an array to store the results of the write instruction 
        DimResults() AsOpcLabs.BaseLib.OperationResult  'OpcLabs.EasyOpc.UA.UAWriteResult
        DimArgs(UBound(Tags)) As UAWriteArguments
        Try
            'iterate through the array and add tags and values to Argument object 
            ForI = LBound(Tags) ToUBound(Tags)
                oTypeCode(I) = System.Type.GetTypeCode(ReadValues(I).Value.GetType())
                Args(I) = NewOpcLabs.EasyOpc.UA.UAWriteArguments("opc.tcp://"& sServerName, _
                                                                  sServerType & Tags(I), _
                                                                   NewOpcLabs.EasyOpc.UA.UAAttributeData(oValues(I)), oTypeCode(I))
            Next
            IfIsNothing(Args) = False Then 
                'Write the items 
                Results = easyUAClient1.WriteMultiple(Args)
            End If
        Catchex As Exception 
            'display an exception to screen 
            MessageBox.Show(ex.Message)
        Finally 
 
            ForI = LBound(Tags) ToUBound(Tags)
                IfResults(I).Succeeded = False Then 
                    OPC_UA_WriteMultipleItems = False 'Bad Write 
                    Exit For 
                Else 
                    OPC_UA_WriteMultipleItems = True    'Good Write 
                End If 
            Next
            'Kill objects 
            easyUAClient1.Dispose()
            IfIsNothing(easyUAClient1) = False TheneasyUAClient1 = Nothing 
            IfIsNothing(Results) = False ThenResults = Nothing 
            IfIsNothing(Args) = False ThenArgs = Nothing
        End Try
    End Function
 

If I switch to WriteValue and try to write to the int tag in the SLC 500, it will work.

I am using TOP Server, Allen-Bradley Ethernet driver, and OPC.Net UA 5.3. I have also had success using a different OPC server and WriteMultiple.

More observations I have:

When using an SLC 500, I cannot write to PLC address unless the Tag NAME is defined in TOP Server. The Tag NAME must match the PLC address. For example: SLC500.SLC500.N7:0

Defining tag name N7:0 and address N7:0 reads and writes properly to N7:0

Defining tag name SSN7:0 and address N7:0 reads properly from N7:0 but cannot write to N7:0

Removing from TOP Server tag name N7:0 and address N7:0 reads properly from N7:0 but cannot write to N7:0

Other tags, such as Strings (ST28:0) or Booleans (B3/0) seem to work OK either way.


Any ideas if this would be related to something weird in the server driver or if it something weird with WriteMultiple.
Last edit: 27 Mar 2014 06:01 by support. Reason: used [code] for better formatting

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