Removing Locked Interconnections, Text References, and Un-deletable Links in CFC Charts

When an interconnection line in a SIMATIC PCS 7 CFC chart becomes locked and cannot be deleted following a block type interface update (such as deleting an I/O pin in the library block), the link has become an orphaned text reference or an invalid database pointer. To resolve this: first, use 'Options > Delete Textual Interconnections' in the CFC editor; if the connection remains stuck, temporarily re-add the deleted pin with its exact original name in the source block, update block types in the chart folder, manually delete the restored clickable connection, and then remove the pin permanently.

Executive Summary

During software refactoring and library updates in SIMATIC PCS 7 (V8.0 through V9.1), engineers frequently modify custom or standard Function Blocks by deleting obsolete I/O pins. If a pin is deleted from a block interface in the Master Data Library while active signal interconnections still target that pin on existing CFC charts, a severe graphical locking condition can occur. Upon updating block types, the target pin vanishes, but the interconnection line remains drawn across the chart sheet to empty space, un-clickable and immune to standard deletion commands. This article details the database mechanics of orphaned interconnections, the 'Temporary Pin Restoration' method, and cleanup procedures.

Architecture and Fundamental Mechanics

Database Mechanics of Orphaned Interconnections and Graphical Link Lockup:

CFC Interconnection Topology:
In the CFC database, a signal interconnection is stored as a bidirectional record connecting SourceBlockID.PinName to TargetBlockID.PinName.
The graphical editor renders lines by calculating coordinate vectors between the physical bounding boxes of the respective pin connectors on the sheet.
The Origin of the 'Zombie Link':
If an engineer deletes a pin from an FB definition in SCL or LAD/FBD and executes Options -> Block Types -> Update, the CFC update engine modifies the block's visual footprint, removing the pin header.
If the update engine encounters an existing chart connection targeting the deleted pin, it fails to resolve the endpoint coordinates. The connection record becomes an 'orphaned pointer' or an unresolved textual interconnection.
Because the target pin coordinate no longer exists, the graphical editor cannot register mouse clicks or selection events on the line endpoint. Pressing Delete or right-clicking produces no response, locking the link in place.
Resolution Strategies:
1. Delete Textual Interconnections: If CFC downgraded the broken link into a textual reference, it can be deleted via the global text reference table.
2. Temporary Pin Restoration (The Universal Remedy): Re-adding the deleted pin with its exact historical name and data type restores the coordinate anchor point. This re-enables graphical selection, allowing the engineer to cleanly delete the line before removing the pin permanently.
3. Project Reorganization: Rebuilding project database tables via 'Save As with Reorganization (slow)' cleans up residual relational pointers.

Step-by-Step Implementation Procedure

Step-by-Step Procedure to Remove Locked and Un-deletable CFC Interconnections:

Attempt Automated Textual Interconnection Deletion:
- Open the affected CFC chart in the CFC editor.
- Select menu Options -> Delete Textual Interconnections....
- In the dialog, inspect the list of unresolved text connections.
- Select the offending connection and click Delete.
- If the line disappears, proceed directly to Step 4.
Execute the Pin Restoration Method (If Line Remains Stuck):
- Open the block's source code (SCL source file or LAD/FBD block) in the Master Data Library.
- Re-declare the deleted input or output pin using its exact original name and exact data type (e.g. OldPin_Act : BOOL;).
- Recompile the block source code to generate an updated block in the library.
- In the CFC editor, select menu Options -> Block Types.
- Select the modified block and click Update....
- The block instance on the chart updates its graphical interface; the previously missing pin reappears, and the stuck interconnection line reconnects cleanly to the pin terminal.
Cleanly Delete the Interconnection:
- Click the visible connection line on the CFC chart to highlight it.
- Press the Delete key (or right-click the line -> select Delete Connection).
- Confirm the line is completely removed from the chart.
- Return to the block source code in the library and remove the temporary pin declaration.
- Recompile the block and update block types once more in the CFC chart folder (Options -> Block Types -> Update). The block now displays its desired interface with zero ghost connections.
Perform Project Reorganization and Consistency Check:
- Close all CFC charts.
- In SIMATIC Manager, select File -> Save As... with Reorganization (slow).
- Open the reorganized project; in CFC, run Options -> Check Consistency -> Charts as Program.

Verification

Verification Procedure:
1. Graphical Verification: Open the CFC chart. Confirm that the stuck interconnection line is completely gone and the block interface displays the correct pin configuration.
2. Consistency Check Verification: Execute Options -> Check Consistency -> Charts as Program. Confirm that the log reports zero open textual references, zero interconnection errors, and zero warnings.
3. Compilation Test: Run Chart -> Compile -> Charts as Program. Confirm that compilation succeeds with 0 errors.

Limitations and Operational Precautions

Operational Precautions and Refactoring Guardrails:
- Always sever all chart connections to an I/O pin before deleting or renaming that pin in the master library.
- Version Update Impacts: Modifying block interfaces and updating block types across a plant changes block interface timestamps. In PCS 7, this will prevent delta downloads and force an AS STOP download unless using the CPU 410 Type Change in RUN (TCiR) mechanism.
- Fixed in Updates: Siemens addressed several graphical connection lockup bugs in PCS 7 V9.0 SP3 / CFC V9.0 SP3 Upd1; ensure the latest engineering hotfixes are installed.

Engineer FAQ

Why does a CFC connection line become locked after deleting a block pin?

Deleting a pin without removing its connection leaves an orphaned database pointer. Because the pin anchor coordinate no longer exists, the graphical editor cannot register mouse clicks to select or delete the line.

What is the quickest way to delete an un-clickable interconnection line?

Temporarily re-add the deleted pin with its exact original name in the source block, update block types so the pin reappears, delete the now-clickable line, and then remove the pin permanently.

Where is the 'Delete Textual Interconnections' command located?

In the CFC editor menu bar under Options -> Delete Textual Interconnections....

Does modifying a block interface allow delta download in RUN?

Standard S7-400 CPUs require an AS STOP download when block interfaces change. CPU 410-5H supports Type Change in RUN (TCiR) under specific engineering constraints.

Can renaming a pin cause the same locked link issue?

Yes. Renaming a pin is internally treated as deleting the old pin and creating a new one, causing identical orphaned connection issues if the link was not deleted first.