Completely Deleting Legacy AS Nodes in SIMATIC PCS 7 DBA (Database Automation for 505 / Third-Party AS)

In SIMATIC PCS 7 using Database Automation (DBA) for legacy controller integration (such as SIMATIC 505 / TI 505 or OPC data sources), deleting an AS Node in the DBA tree while its generated communication tags remain locked in WinCC Tag Management causes the node and system tags (e.g. @S505_PLC31#RawEvent, @S505_PLC31_License) to persist across compilations. To completely remove a deleted AS Node and its locked WinCC channel connections, engineers must unassign all block instances in DBA, perform an AS-OS compilation with 'With memory reset' to remove instance tags, delete the AS Node in DBA, execute a Full Compilation in DBA to purge channel unit drivers, and delete remaining orphan connection objects in WinCC Tag Management.

Architecture of PCS 7 Database Automation (DBA) for Non-S7 Controllers

In hybrid and modernization projects, SIMATIC PCS 7 integrates non-S7 automation systems—specifically legacy Texas Instruments / Siemens SIMATIC 505 controllers (TI 505, 545, 555), Allen-Bradley PLCs, and third-party OPC servers—using Database Automation (DBA) (e.g. DBA 505 V7.0, V7.1, or DBA V8.0 6ES7658-2CX18-0YB0).

DBA acts as an engineering bridge that mimics the native S7 AS-OS compiler:
1. It imports controller tag definitions from programming tools (such as TISOFT, Workshop, or CSV dumps).
2. It maps controller memory locations to standardized PCS 7 APL technological blocks (motors, valves, analog inputs).
3. During compilation, DBA automatically generates communication channels, connection objects, structure tags, and internal system tags in WinCC Tag Management (e.g. @S505_PLC31#RawEvent, @S505_PLC31_License).

Why Deleted AS Nodes and System Tags Persist in WinCC Tag Management

Commissioning engineers frequently encounter a deadlock when retiring an old controller:

The engineer unassigns tags in DBA, right-clicks the AS Node (e.g. PLC31), and selects Delete.
The node disappears from the DBA project tree.
However, running a delta or full compilation in DBA fails to remove the node from WinCC. The communication unit in WinCC Tag Management still lists the deleted PLC with its two system tags (@S505_PLC31#RawEvent and @S505_PLC31_License).
Attempting to delete the connection or tags directly in WinCC Tag Management fails with an error: The connection is locked by an external engineering tool (DBA).

The root cause: When an AS Node is deleted from DBA before executing a compilation that de-registers the physical communication channel, DBA loses its internal reference pointer to the deleted node. During subsequent compilations, DBA only reconciles nodes present in its active XML database; it has no transactional record instructing it to delete the ghost channel in WinCC.

Comparison of DBA Compilation Modes and Tag Lifecycle States

The following table compares DBA compilation mechanisms when retiring controller nodes:

Deletion WorkflowDBA Node StatusWinCC Channel ConnectionSystem Tags (@S505_*)Resulting StateImmediate Delete Node in DBANode removed from treePersists in WinCC; lockedPersist permanentlyDeadlocked; orphan tags cannot be deletedUnassign Tags -> Delta Compile -> Delete NodeUnassigned, then deletedRetains channel driverRetains system tagsIncomplete cleanupStructured 4-Step Reconciled PurgeRe-added, emptied, purgedCompletely purged from WinCCCompletely removed100% Clean system stateWinCC Direct Manual DeletionUnchanged in DBALocked by DBA tool attributeLockedBlocked by WinCC security layer

Step-by-Step Procedure to Cleanly Purge an AS Node from DBA and WinCC

Follow this procedure to resolve the deadlock and completely remove the retired AS Node and its ghost tags:

Recreate the Ghost Node in DBA (Restoring the Pointer):
- In DBA, right-click the controller network and select New AS Node.
- Name the node with the exact identical name as the deleted PLC (e.g. PLC31).
- Configure its communication parameters matching the old node.
Ensure All Tags Are Unassigned:
- In the upper pane of DBA, verify that zero process tags or instances are assigned to this node (unassign any tags).
Compile DBA with Memory Reset Option:
- In DBA, select OS -> Compile.
- Select Entire OS (Complete Compilation) with the option With memory reset (Mit Urlöschen der OS-Variablen) checked.
- Click Start. DBA synchronizes with WinCC Tag Management, identifying that PLC31 has zero tags and clearing instance links.
Properly Delete the Node in DBA:
- Now right-click PLC31 in the DBA project tree and select Delete.
- Select OS -> Compile again with 'Complete Compilation'.
- DBA detects the node removal transaction and sends an explicit deletion command to the WinCC channel unit.
Clean Up Residual Channel Objects in WinCC:
- Open WinCC Explorer on the ES.
- Open Tag Management.
- The PLC31 channel unit and its system tags (@S505_PLC31#RawEvent, @S505_PLC31_License) are now unlocked and can be deleted cleanly.

Verification

Verify complete node removal in WinCC and DBA:
1. In DBA, confirm that PLC31 does not appear anywhere in the project tree or instance list.
2. Open WinCC Tag Management. Confirm that the communication connection for PLC31 under the SIMATIC 505 / Third-party channel is completely gone.
3. Search for tags containing PLC31. Confirm that zero tags exist in both internal and external tag groups.
4. Perform a test delta compile in DBA; verify that 0 errors are reported and no ghost tags are recreated.

Limitations and Operational Precautions

WinCC Project Duplication: After purging the node on the ES, use Project Duplicator to update runtime servers. Never manually edit tag tables directly on runtime servers.
DBA and PCS 7 Version Alignment: Ensure your DBA version strictly matches the PCS 7 version (e.g. DBA 505 V7.1 SP3 on PCS 7 V7.1 SP3; DBA V8.2 on PCS 7 V8.2). Mixing older DBA versions with newer PCS 7 builds causes database schema synchronization failures.
Process Object License Recovery: Deleting an AS node in DBA frees up WinCC OS Process Object (PO) licenses counted by the retired controller once a full compile is completed.

Engineer FAQ

Why does WinCC say 'The connection is locked' when I try to delete a tag?

WinCC Tag Management prevents deleting tags generated by external engineering tools (such as DBA, CFC, or STEP 7) to maintain database consistency. The tag must be deleted from the originating tool (DBA) via a complete compilation.

What are the @S505_* tags in WinCC?

They are internal communication and license supervision tags automatically created by the SIMATIC 505 channel unit in WinCC for raw event buffering and controller licensing.

Why did deleting the node in DBA not delete the connection in WinCC?

Deleting the node in DBA before running an empty compilation severed the transactional link. DBA only manages objects present in its active tree; it does not remember deleted nodes unless they are purged through a synchronized compilation.