【正文】 ycle will register in same group. Also, you should be carefully CPU performance to create over groups because OPC Server create a thread for each group.Dim ClientHandles(16) As LongDim OPCItemIDs(16) As StringSet Mygroups = Set Mygroup = (Group1) = 1000 = FalseFor i = 1 To 16 ClientHandles(i) = i OPCItemIDs(i) = Device1 + .D + Format(i)Next iSet Myitems = 16, OPCItemIDs, ClientHandles, ItemServerHandles, ItemServerErrors = TrueAdvise and CallbackImplements event handler of OPC Group object for advice mode. The OPC Server read data for each cycle and if changing the value, callback to client application. The quality flag is normally 39。0xC039。, when occurred error, it will be turn to other value. = TruePublic Sub Mygroup_DataChange(ByVal TID As Long, _ ByVal NumItems As Long, Chd() As Long, ItemValues() As Variant, _ Qualities() As Long, TimeStamps() As Date) For i = 1 To NumItems ItemValues(i) + : + TimeStamps(i) + _: + Qualities(i) Next iEnd SubSync Read/Write and ASync Read/WriteThe OPC has two ways of data access, Synchronize and Asynchronous. In Synchronize, the client application must be wait for pleting server work. But the client application can confirm server transaction is normally pleted because the OPC Server returns the result on pleting the munication work. This is a normally style of procedure.In Asynchronous mode, the OPC Server turns the handle to client as soon as receiving the request and proceed the transaction on background. After pleting this work, calls handler of client application. Asynchronous mode cut down wait time for munication and be able to run client application.Caution: Asynchronous access is enabled under advice mode.39。Sync Read OPCDevice, 16, ItemServerHandles, ItemValues, ItemServerErrors, ItemQualities, ItemTimeStampsFor i = 1 To 16 ItemValues(i) + : + ItemTimeStamps(i) + : + ItemQuality(i)Next i39。Sync WriteFor i = 1 To 16 ItemVal(i) = iNext i 16, ItemServerHandles, ItemVal, ItemServerErrorsFor i = 1 To 16 If ItemServerErrors(i) 0 Then MsgBox Write ERROR + Format(i) End IfNext i39。Async Read（TransactionID=10, CancelID=11） 16, ItemServerHandles, ItemServerErrors, 10, 11Private Sub Mygroup_AsyncReadComplete(ByVal TransactionID As Long, ByVal NumItems As Long, _ ClientHandles() As Long, ItemValues() As Variant, Qualities() As Long, _ TimeStamps() As Date, Errors() As Long) AsyncRead Comp + Chr$(9) + Time$ + Chr$(13) + Chr$(10)End Sub39。Async WriteDim ItemVal(ItemCount) As VariantFor i = 1 To ItemCount ItemVal(i) = iNext i 16, ItemServerHandles, ItemVal, ItemServerErrors, 100, 101Private Sub Mygroup_AsyncWriteComplete(ByVal TransactionID As Long, _ ByVal NumItems As Long, ClientHandles() As Long, Errors() As Long) AsyncWrite Comp + Chr$(9) + Time$ + Chr$(13) + Chr$(10)End SubCache ReadIn cache read operation, OPC Server doesn39。t access the physical device and return the last data on memory. The OPC Server read and caches the value every each will be able to access on high speed if not need newest value. OPCCache, 16, ItemServerHandles, ItemValues, ItemServerErrors, ItemQualities, ItemTimeStampsFor i = 1 To 16 ItemValues(i) + : + ItemTimeStamps(i) + : + ItemQuality(i)Next iI am trying to develop an opc da client using .net technology.Have gone through the documents on opc and opc client and all,but am still not sure how to implement it, can someone give me a direction on how to start with it?59 Answers FoundAnswer 1can you please provide some additional details on exactly what you39。re trying to do and any other relevant info that I can pass on to our support engineer?thanks,brenda (ISV Buddy Team)Answer 2Hey Ksona,I was just speaking to a college of mine about DA cleints this morning. Have your checked out theopc Exchange at ?I know that Eric Murphy is an OPC genius, and he can probablygive you a hand, or point you in a great direction.You can also me and I can see if one of my college39。s has some time to help you out? I39。m curious as to what devices you are trying to access?Answer 3Genius? That39。s a wee bit over the top, let39。s just say I39。ve experienced a thing or two about OPC. However, if you39。re fishing for a response, flattery will get you everywhere :)As the other replies pointed out, the question is a bit open ended. 39。using .NET technology39。 offers a few possibilites, depending on your develpoment language C, , managed C++, etc.The easiest way, would be to make use of the OPCclient .NET wrapper supplied by the OPC Foundation. You do have to be a member to access this, however that offers other advantages such as invitations to the OPC Interoperabilty events to test your client against other vendors.If that39。s not an option, I have seen applications that make use of the OPC Automation dll. This was originally intended for VB apps, but some vendors have upgraded the automation interface to work with You would have to ask specifically because not all versions do.Otherwise, you are looking at writing an application that interfaces to unmanaged COM interfaces. From an programatic point of view, an OPC client would be no different from any other COM client. If you39。re new to OPC, this is not a trivial task...Answer 4Hey Ksona,I agree with what Eric Murphy said, that your best bet is to get the libraries off of theopc Foundation39。s site. But you might want to try Visi39。s excellent .NET interface library here:Again, do not assume that this is of any mercial quality amp。 stability, you39。re best option is to get the OPC Foundation39。s.Hope this helps!SteveAnswer 5Hi Eric, Sounds like you know what you39。re talking about ... Can I also butter you up and find out if you know anything about using anopc interface in that was designed for VB6. The problem is the that Rockwell use to interface to their OPC server (RSlinx). It only accepts Arrays with lower bounds of 1 which is not possible in . (seerefs below)1) 2) I only dimly understand the article on It seems to be saying that if I was using VC++ I could write some kind of code which would make be able to use the OPC interface which was COM and written for VB6. If I was using C++ I39。d be laughing. I39。m not. :)... and while the C++is interesting and gives me hope, I39。m working with and I39。m still trying to figure out how I can use the OPC interface designed for VB6 with . Why do I even need ? If OPC is a standard, can I not just use any OPC interface and hope that RSLinx (the Rockwell OPC server) answers with the right data? Is there not a General OPC interface dll?Puzzled from LeicesterAndrew Smith|at|Answer 6You can use or c with rslinx39。s COM dll.You just add the reference to to your project and use its classes.To pass an array to a OPC method, just dim the array to n+1 and fill it starting at index 1.The method will return object arrays that you will read starting at index 1. You have to cast to the specific types to get the values.Excuse me for my bad grammar.I hope this helps.Answer 7I was looking for some help developing a C OPCclient using the OPCAutomation wrapper when I stumbled upon your conversation. Here is a link to a sample OPC client that helped shed some light on using .Net todevelop OPC clients using the wrapper.Answer 8Thanks Everyone,Right now, i am using Advasol opc clientponents for myopc client development. It looks ok till now :)Answer 9Andrew, Perrakus is correct in his discription on using the Automation dll with . Once you add the reference, you can access all the classes just like in VB6. Since doesn39。t seem to support the 39。Option Base 139。 you will have to handle the offset yourself. A little bit of background on the Automation wrappers. There actually is a Generalopc interface dll. It39。s called the Automation Wrapper, or . When the first OPC DA specifications were released, the OPC Foundation did not wish to support plied applications, so the source code for the was supplied to all OPC members. Each vendor then repiled the code under their own GUID(Rockwell renamed it ). In November of 2005, the OPC Foundation decided to take the responsibility of maintaining various applications (DA Wrapper, Compliance tests, proxy stubs etc). All the bug fixes various vendors had applied over the years was piled and the OPC Foundation released the 39。official39。 . Many vendors already were supporting 39。their39。 wrapper so continue to ship the vendor branded version. Version of the automation wrapper has been tested with on Win2000 and WinXP. You can read the details on the Foundation website at If you are an end user, you need to get the binaries from your OPC Vendor (I assume it39。s Rockwell in your case) Cheers and Good Luck. Eric Answer 10When i try add an Opc group, i get te following error message:Opc Server add group failed with exception: Unable to cast object of type 39。39。 to type 39。39。Does anyone help me?Answer 11Post your code here to have a look at it, leandroAre you using a reference to COM OPC?Altough the exception is very clear.Answer 12I have the same problem .I am using this sample code ( ) Does anybody have a solution for this ?Answer 13The link you posted doesn39。t work.Post the code in this forum.Answer 14Sorry , this one should workHere a sample of the code:39。 connect OPCServ