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| Command | Syntax | Meaning |
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| STWATCH | STWATCH StationName | Tell The command sends commands for the synchronous reading of values of all configured I/O tags (regardless of whether data access type is set to “Async I/O 2.0”, "Async I/O 3.0", or “Synchronous I/O”) |
| STCOMMAND | STCOMMAND StationName DISCONNECT | Tell The command encloses immediately closes the active OPC connection of the line (the parent of "StationName"). Then, the system is restarted and the connection is reinitiated. If remote access is used and a backup OPC host is configured, the servers are interchanged ("OPC Host" for "Backup Host" or vice-versa). |
| STCOMMAND StationName CONNECT_PS | Closes the active OPC connection and enforces connection to the primary OPC server "OPC Host". It is important only for remote access. | |
| STCOMMAND StationName CONNECT_BS | Closes the active OPC connection and enforces connection to backup OPC server "Backup Host". It is important only for remote access. |
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For users working under Windows XP with ServicePack2 Service Pack 2 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.
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then it is necessary to add a user in the context of whose 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 "Access Permissions" and "Launch and Activation Permissions" parameters and enable "Remote Access" / "Remote Activation". It is a problem connected with establishing the callback connection with the OPC server. In this case, the roles are reversed, and the OPC client (i.e., KOM process) works as a DCOM server. Adding this user and enabling the remote access enables establishing the callback procedures between the OPC client and the OPC server. Call-back procedures are necessary for acquiring the values from the OPC server in the "Async I/O 2.0" and "Async I/O 3.0" asynchronous modes.
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Due to Microsoft security updates (e.g., KB5004442), OPC communication stops working after applying the updates. Sometimes, even setting the Authentication Level parameter does not help. For example, when the D2000 KOM is on a patched/new Windows (e.g. Windows 11) and the OPC server is on an unpatched/old Windows (e.g. Windows XP, for which patches do not even exist), errors such as:
can be seen, while in the Windows system log there are messages like: The server-side authentication level policy does not allow the user SRV-KOM1\testuser SID (S-1-5-21-776983252-1896133985-1590337295-1001) from address 10.12.1.50 to activate DCOM server. Please raise the activation authentication level at least to RPC_C_AUTHN_LEVEL_PKT_INTEGRITY in client application. The solution, according to Microsoft, is to update/reinstall the old Windows. |
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If the OPC server is configured to run under "The interactive user" on the If the OPC server is configured to run under "The interactive user" on the Identity tab of the "Properties" dialog window, it may cause the OPC server to be available only when a user is logged on to the computer. We recommend changing this setting to "The launching user", "This user", respectively or "The system account". |
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In the specific case for the OPC communication to work, it was required:
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