OPC Data Access 2.05 & 3.0 Client Communication Protocol

Supported device types and versions of devices 
Communication line configuration
Communication station configuration
I/O tag configuration
Browsing of the OPC server address space
Historical Data Access
Tell commands
DCOM configuration for connecting a remote OPC server
Errors and problems
Literature
Changes and modifications
Document revisions

Supported device types and versions

The protocol supports the client side of a communication with OPC (OLE for Process Control) DA (Data Access) servers according to the OPC DA specification ver. 2.05A and 3.0. It also supports the client side of communication with OPC HDA (Historical Data Access) servers according to OPC HDA specifications ver. 1.20.

Communication line configuration

• Communication line category: OPC.
• OPC parameters:
• OPC Host: Only Remote entrance requires it. Computer, where the program D2000 OPC Server is installed in - it is defined for OPC server type "Remote" only (maximum string: 50 characters). You can define names according to the UNC convention (e.g. \\server or server), DNS domain names (e.g. domain.com, example.company.com) or IP address (196.54.23.113).
• Backup Host: Only Remote entrance requires it. It is backup OPC host. If the parameter is defined, after the communication has failed, the process D2000 KOM is attempting to establish connection alternately with the OPC host and Backup host.
• OPC Server: Name (ProgID) of the OPC server (maximum string: 50 characters).
• Server Type: according to the server type – InProc, Local or Remote.

Communication line parameters

Following communication line parameters can be configured for protocol "OPC Data Access 2.05 & 3.0":

Tab. No. 1

Note:

Fatal abort of communication with OPC Server causes the COM/OPC errors at callings:

• GetGroupState of interface IOPCGroupStateMgt,
• "Write" of interface IOPCASyncIO2, IOPCASyncIO3 and IOPCSyncIO2,
• "Read" of interface IOPCASyncIO2, IOPCASyncIO3 and IOPCSyncIO2.

Communication station configuration

Communication protocol: OPC Data Access 2.05 & 3.0. 

Station address requires:

• OPC Group Name - maximum string: 80 characters. This name is only formal in most cases and has no direct relation to the address scheme of devices communicating with the OPC server. The name of group must be unique, two stations cannot the same OPC Group Name within one link.
• Type -  data access type. You can chose one of the Async I/O 2.0, Async I/O 3.0 and Synchronous I/O options. The Async I/O 2.0 option - the asynchronous OPC interfaces IOPCAsyncIO2 and IOPCDataCallback (OnDataChange and OnReadcompleted call-back procedures) are used for data reading. The Synchronous I/O 2.0 option - OPC interface IOPCSyncIO is used. The Async I/O 3.0 option - OPC interfaces IOPCAsyncIO3 and IOPCDataCallback (OnDataChange and OnReadCompleted call-back procedures) are used for value reading of OPC items
• Create Active - if the option is checked, the OPC group is active and OPC items in this group get values. If the option is not checked, the OPC group and items are initialized, but  the OPC items do not get values. It is possible to block the OPC group - station temporarily. The option controls the pActive parameter of SetState call of the OPC interface IOPCGroupStateMgt.
• Update Rate - it is given in milliseconds and defines the maximum speed of OPC item value changes for the option Async I/O 2.0 or Async I/O 3.0. It is transferred as parameter pRequestedUpdateRate of SetState call of OPC interface IOPCGroupStateMgt. Warning - the information, set in tab Time parameters in dialog window Communication station - configuration dialog box defines the read rate of OPC items.
• % Deadband - the parameter range is from 0.0 up to 100.0%. The parameter can be only used for analog type of items and determines the minimal change of the item for sending the value from the server to clients. For calculation, the OPC server uses the range defined by parameters High EU and Low EU, which can be get by using the interface IOPCItemProperties. Default value of this parameter is 0.0. Value of % Deadband is transferred by means of parameter pPercentDeadband of the SetState call of the  OPC interface IOPCGroupStateMgt.
  Note: The protocol OPC Client described in this topic does not support the OPC interface IOPCItemProperties. For further information read up the document listed in the section Literature.
• Time Bias - If OPC server and OPC client do not run in the same time zone, the parameter (given in minutes) will be used for the correct calculation of the value time of the OPC item - time stamp. Default value of the parameter is 0 (zero). For further information read up the documents listed in the section Literature.

Station protocol parameters

The following station protocol parameters can be defined:

I/O tag configuration

Possible I/O tag types: Ai, Ao, Ci, Co, Di, Qi, Dout, TiA, ToA, TiR, ToR, TxtI, TxtO.

I/O tag address requires to define OPC Item ID (maximum string: 200 characters). If OPC server supports interface IOPCBrowseServerAddressSpace, the address OPC Item ID may be selected directly from the address list supported by OPC server (it is needed to click on button "Browse Items...", see the section Browsing of OPC server address space.
Note: if I/O tag's address is specified as %IGNORE, such an I/O tag will be ignored.

Further required parameters (OPC Item Parameters) are:

• Type - required data type VARIANT. Default value is Empty/Default (VT_EMPTY), - the OPC server makes a decision on the VARIANT type of the item.
• Item Active - if the option is checked, the item will be active and get values from the server. The option is transferred by the parameter bActive of the pItemArray structure into the AddItems call of the OPC interface IOPCItemMgt.
• Bit Index - bit number. It is defined as a number within the range of 0..31. It can be only used for the Di and Dout value types. Value received from the OPC server is being converted to 32 bit unsigned number and the binary value of the I/O tag is the value of particular Bit Index. The conversion is allowed only for the VARIANT values of integer types (e.g. VT_UI1, see the adjusted parameter Type).
• Array Index - the option (a number within the range of 0..32767) determines the index in the array of received VARIANT value from the OPC server of the Array type. Array value on the defined position is assigned to the value of the I/O tag.

The protocol supports the configuration of tab Destination of I/O tag. If the value of OPC item is of Array type, the communication protocol copies the values of array from the item ArrayIndex into column of structured variable. The size of structured variable is taken into consideration. If the array VARIANT is smaller than number of structured variable rows the empty rows of structured variable will be invalid. If the number of structured variable rows is smaller than array VARIANT, the values which are remaining are ignored.

Browsing of the OPC server address space

Clicking on button "Browse Items..." in the Address tab of I/O tag dialog box opens another dialog window "OPC Item Browser".

Here the user can choose the items from the OPC server address space. The item representation can be "Hierarchical" or "Flat". Some of the OPC servers do not support the "Hierarchical" representation (the button "Hierarchical" is disabled). If both the representations are supported the "Hierarchical" may be switched over to "Flat" and vice-versa.

• Hierarchical - enables browsing of the OPC server address space according to the logical hierarchical groups and subgroups. The dialog box "OPC Item Browser" is divided into two parts:
  • hierarchical tree structure (top part)
  • list of OPC items (OPC tags) belonging to the selected branch (bottom part)
• Flat - displays all the available OPC items in one linear list.

OPC Item ID may be selected by double click on it. This item then occurs in the text field OPC Item ID in tha Address tab of I/O tag dialog box and "OPC Item Browser" dialog window will be closed. To close the window without changes click on button "Cancel".

On the top part of the dialog window there are filter options. Text "Filter" allows to show only the items according to mask (some of the OPC servers supports so-called star convention).
"Data Type Filter" allows to show the items containing a suitable data type. The option "Empty/Default" is default and enables to view all the items.
User must define whether the filter should be applied on the hierarchical tree structure (check button "Apply to the branches") or also on the OPC items (check button "Apply to the items").

According to the access rights, only readable items are displayed (check button "Browse readable items") or writable one (check button "Browse writeable items"). Default settings - both possibilities are enabled.

The changed conditions come into effect by clicking on "Refresh" button.

Note: In versions from 20th December 2018 and newer, recycling of browser dialog has been implemented. If the dialog is closed by the Close button or after selecting a tag, it is actually only hidden and it is available for browsing by another I/O tag within the same station so that the tree structure of the browsed objects is preserved. Clicking on the close icon at the top right corner will cause the dialog to be really closed.

Historical Data Access

Implementation of this protocol partially supports the specification of OPC HDA (Historical Data Access). The synchronous reading of raw data is supported. TELL command GETOLDVAL activates the reading of historical values. The asynchronous option IOPCAsyncIO of mode for OPC DA should be set to continuously read both the historical data and current one.

Tell commands

DCOM configuration for connecting a remote OPC server

Remote browsing/local registration of OPC server

D2000 KOM Process (version 7.01.020 rel. 055 and higher) supports the getting GUID OPC Servers from ProgID on remote computers through the DCOM interface by OPCENUM utility (remote browsing). The local registration of OPC server at client is not required if the utility/windows service OPCENUM has been installed on the local PC with D2000 KOM process as the OPC client and on the remote PC as the OPC server and the access rights allows the remote browsing. The utility OPCENUM is a part of package OPC Core Components Redistributable available on http://www.opcfoundation.org/ or as the part of OPC Server installation package.

If this error occurs (see the section COM/OPC errors record):

ERROR: OPCServerName caused COM/OPC error 80040153H on CoCreateInstanceEx(IID_OpcServerList), Error string : Invalid value for registry

it is necessary to install the OPC Core Components Redistributable also on the OPC client (KOM process). The registration of OPC Server is optional. To register use one of the two ways:

1. Some OPC servers are supplied together with installation programs supporting the connection of OPC clients (third side) to the remote OPC server. This installation programs are called e.g. OPC Server Connect, etc. After installation, the OPC server (ProgID) appears in the list of OPC servers on the client's computer. D2000 OPC client uses this information for acquisition of CLSID from given ProgID (see the section Communication line configuration). A OPC server registered by this way, of course, can't be run on the client side.
2. Manual registration of the OPC server on the client side. Proceed as follows:
   1. Copy the OPC server (from the computer where has been installed) into an auxiliary directory on the client side (computer).
   2. Run the command line from the directory.
   3. Register the OPC server. If the OPC server name is e.g. OPCSERVER.EXE, then you enter: OPCSERVER.EXE /regserver and press ENTER. If the OPC server is only as .dll, use the system utility regsvr32. 
   4. The auxiliary directory and files can be deleted.

Always study the OPC server manual from its manufacturer in details and confront it with the procedures described above.

Setting the access rights to OPC Server

As OPC DA standard uses COM/DCOM technology, the connecting to the remote OPC server is checked for Windows operating system access rights. On both the local (OPC client) and remote (OPC Server) computer, there must be created the same user (with the same password) and the user must be logged on the client side or the KOM process (running as Windows service) must start up under the account of this user.

1. On the computer with OPC server use the command "dcomcnfg" to start "Component Services" (or start it in "Administrative Tools").
2. Select "Properties" menu in  "Component Services" -> "Computer" -> "My Computer".
3. Make sure that DCOM is enabled, i.e. parameter "Enable Distributed COM on this computer" on "Default Properties" tab is checked.
4. In the list of components (branch "DCOM Config" under "My Computer"), select required OPC server and open the dialog box containing its parameters (Properties). Click the Security tab.
5. The parameter "Launch And Activation Permissions" set to Customize and click Edit... button.
6. Find the required user and if is not in the list, add him/her into..
7. Enable the options "Remote Launch" and "Remote Activation".
8. The parameter Access permission set to Customize and click Edit... button.
9. In the "Identity" tab check whether "The launching user" or "This user" option is enabled, which is also the checking of user account that you configure. Typically, we recommend the setting "The launching user". If some problems occur, try direct setting "This user". In any case, be careful about setting "The interactive user", which is absolutely not recommended! The OPC server can be accessible and started only if some user is interactively logged on to computer with OPC server. This setting leads to the problems such as unavailability of OPC server, e.g. after its starting until any user is logged on.
10. If you must use the setting "The system account (services only)", i.e. OPC server works as Windows service, watch the level of access rights of "SYSTEM" according to above mentioned rules.

Wrong setting of access rights will probably causes an error (see the section Errors and problems - COM/OPC error reports):

|E|> ERROR: ServerProgID caused COM/OPC error 80070005H on CoCreateInstanceEx(CLSCTX_REMOTE_SERVER), Error string : Access is denied.

Watch logs in the Event Viewer.

The problem can be partially solved when you add the Everyone group into Launch Permissions and Access Permissions. To ensure, that the OPC server will be run under some user (not under SYSTEM account), open the tab Identity and define the data for the option This user. In this case, the OPC server is not safe.

If the KOM process runs as Windows service it cannot use the parameters /X1 or /X2, because it does not work under the logged on user but under SYSTEM account and access rights verification executed by the OPC server fails. Use the start up parameter /X4".

If it is not possible to start up the KOM process with parameter /X4, check the user to be included in Policy Log on as a service. Open the Control Panel -> Administrative Tools -> Local Security Policy -> Local Policies -> User Rights Assignment -> Log on as a service.

For users working under Windows XP with ServicePack2 or later operating systems, it is recommended to change the parameter Network access: Let Everyone permissions apply to anonymous users (Local Security Policy -> Local Policies -> Security Options) to the value of Enabled.

If there occurs similar error like this:

|E|> ERROR: ServerName caused COM/OPC error 80070005H on Advise(IID_IOPCDataCallback), Error string : E_ACCESSDENIED Access is denied.

there is necessary to add a user in context of whose the communication runs. In "Component Services" on the computer with OPC client (KOM process) add this user to the list of users on the "COM Security" tab -> "Edit Limits", for both the parameters "Access Permissions" and "Launch and Activation Permissions" and enable "Remote Access" / "Remote Activation". It is problem connected with the establishing the call-back connection with OPC server. In this case, the roles are reversed and OPC client (i.e. KOM process) works as DCOM server. Adding this user and enabling the remote access enables establishing the call-back procedures between OPC client and OPC server. Call-back procedures are necessary for acquiring the values from OPC server in the asynchronous mode "Async I/O 2.0" and "Async I/O 3.0".

Errors and problems

When starting or during the course of communication, the following error reports could occur. For an easier identification of the problem, set the communication tracking level at least to the level Monitor, or temporarily to the level Monitor & disk in the configuration dialog box of particular communication line. If you select the level Monitor & disk, the file line_name.LOG containing all debug and error logs will be created in the subdirectory /TRACE of the application directory on the computer with running process D2000 KOM.

COM/OPC error reports

The error report described in the section Errors and problems are generated on a high level of OPC client. Most of the errors will also contain an error report on the COM/OPC level. Format of such error reports is as follows:

WARNING/ERROR: ServerProgID caused COM/OPC error ErrorCodeHexadecimal on CallDescription, Error string : ErrorDescription

For example:

WARNING: Matrikon.OPC.Simulation.1 caused COM/OPC error 80010108H on IOPCGroupStateMgt::GetState(), Error string : The object invoked has disconnected from its clients.

ERROR: Matrikon.OPC.Simulation.1 caused COM/OPC error 800706BAH on IOPCSyncIO::Read(), Error string : The RPC server is unavailable.

The error reports are important for the problem analysis and will be required by the Ipesoft's technical support if any problem occurs.

Literature

The documents are available on http://www.opcfoundation.org/.

• OPC FOUNDATION, Data Access Custom Interface Standard, Version 2.05A, June 28, 2002.
• OPC FOUNDATION, Data Access Custom Interface Standard, Version 3.00, March 4, 2003.
• OPC FOUNDATION, OPC Common Definitions and Interfaces, Version 1.0, October 27, 1998.
• OPC FOUNDATION, Using OPC via DCOM with Microsoft Windows XP Service Pack 2, (C) 2004 OPC Foundation Inc.

The others:

• OPC DCOM White Paper, Richard C. Harrison, Intellution Inc. © Intellution Inc. 1998

Changes and modifications

• January 3rd, 2003 - added the parameter UPDATE_RATE, value arrays.
• January 23rd, 2004 – revised parameters group/item, error reports and DCOM.
• November 22nd, 2005 - new protocol parameters implemented.
• October 10th, 2007 - parameters of protocol Async I/O 3.0 update
• December 3rd, 2007 - added the information about destination column
• March, 2009 - added the support of HDA
• February, 2010 - OPC Item browsing
• March, 2013 - tell commands

Document revisions

• Ver. 1.0 – February 9th, 2000
• Ver. 1.1 - January 3rd, 2002
• Ver. 1.2 - January 23rd, 2004
• Ver. 1.3 - November 22nd, 2005
• Ver. 1.4 - October 10th, 2007
• Ver. 1.5 - December 3rd, 2007
• Ver. 1.6 - March 13th, 2009
• Ver. 1.7 - February 8th, 2010
• Ver. 1.8 - March 5th, 2013