Managing Runtime Group Synchronization Across OB35 and OB100 When Renaming CFC Charts in SIMATIC PCS 7

In SIMATIC PCS 7 (v8.1 SP1 and higher), renaming a CFC chart automatically updates the corresponding runtime group name in the cyclic interrupt organization block (such as OB35), but does not automatically rename runtime groups in initialization or acyclic organization blocks (such as OB100 startup routines). This occurs because the CFC editor creates independent runtime groups across different OBs when blocks possess startup tasks ({ S7_tasklist := 'OB100' }). Renaming the chart synchronizes only the primary cyclic runtime group. To maintain structural consistency, open the Runtime Editor in CFC, locate the orphaned OB100 runtime group, and rename or reorganize it manually.

CFC Runtime Group Architecture and Multi-OB Scheduling

In SIMATIC PCS 7, when an engineer creates a new CFC chart (e.g. Motor_101):
* Automatic Runtime Group Creation: The CFC compiler automatically creates a corresponding Runtime Group named Motor_101 in the default cyclic interrupt organization block (e.g. OB35 at 100 ms).
* Multi-OB Distribution: Technological blocks from the Advanced Process Library (APL) require initialization during CPU warm restart. Their system attributes { S7_tasklist := 'OB100' } cause the compiler to place their startup algorithms into a separate runtime group inside OB100.
* Chart-to-Group Linking: The CFC editor maintains an internal pointer linking the chart to its primary cyclic runtime group, but links to secondary OBs (OB100, OB86, OB40) operate as auxiliary pointers.

The Asymmetric Renaming Behavior Between OB35 and OB100

When an engineer renames a CFC chart (e.g. from Motor_101 to Feed_Pump_01):
1. Primary OB Renamed Automatically: The runtime group located in OB35 is automatically renamed to Feed_Pump_01.
2. Auxiliary OB Groups Left Unaltered: The runtime group located in OB100 retains the old name Motor_101 (or retains a legacy identifier if copied).
3. Copy-Paste Chart Anomalies: When copying an entire CFC chart to duplicate a technological unit, the cyclic runtime group is renamed, but the initialization blocks in OB100 are frequently merged into a generic group or retain the source chart's name, cluttering the execution structure.

Remediation Procedure - Synchronizing Runtime Groups via Runtime Editor

Follow this procedure to audit and synchronize runtime groups:

[Phase 1: Open CFC Runtime Editor]
   │  • In CFC Editor: Navigate to menu: Edit -> "Run Sequence..." (or press Ctrl + R)
   │  • The left pane displays the organizational execution tree:
   │      - OB100 (Warm Restart)
   │      - OB35  (Cyclic Interrupt 100ms)
   │
[Phase 2: Locate and Rename Desynchronized Runtime Groups in OB100]
   │  • Expand the "OB100" execution branch
   │  • Locate the runtime group containing the renamed chart's startup block
   │    (e.g. still named "Motor_101")
   │  • Right-click the runtime group -> Select: "Object Properties..."
   │  • Update the name to match the chart: "Feed_Pump_01"
   │  • Verify execution order positioning
   │
[Phase 3: Clean Up Empty or Orphaned Runtime Groups]
   │  • In Runtime Editor: Select menu: Options -> "Optimize Run Sequence"
   │  • Delete any empty runtime groups left behind by deleted blocks
   │  • Close Runtime Editor -> Compile CFC (Changes Only)

Runtime Group Synchronization and OB Scheduling Matrix

Compare runtime group behavior across different Organization Blocks:

Organization BlockPurpose in PCS 7Auto-Renamed on Chart RenameImpact if DesynchronizedOB35 (Cyclic)Primary cyclic process executionYes (Automatic)None (Stays in sync)OB100 (Restart)Warm restart initializationNo (Retains Old Name)Administrative confusion during auditsOB86 (Rack Fault)Fieldbus station return monitoringNoDiagnostic driver tracking difficultyOB40 (Interrupt)High-speed hardware eventsNoEvent sequencing uncoordinated

Verification

To confirm that runtime groups are synchronized:
1. In CFC Editor, press Ctrl + R to open the Runtime Editor.
2. Expand OB35; verify that the runtime group name matches the CFC chart name.
3. Expand OB100; verify that the initialization runtime group reflects the identical chart name.
4. Execute Chart -> Compile -> Changes Only; verify that compilation succeeds with zero execution warnings.
5. Switch the CPU to STOP and back to RUN; confirm that initialization logic in OB100 executes without startup faults.

Limitations and Operational Precautions

Never delete an entire runtime group in OB100 without verifying whether it contains essential startup blocks for multiple charts. Deleting startup blocks prevents APL blocks from initializing internal feature bits, causing blocks to remain in an uninitialized state following a controller power cycle. Always use the Runtime Editor to inspect group contents before deletion.

Engineer FAQ

Does an unsynchronized runtime group name in OB100 affect CPU execution?

No. The CPU executes machine code based on block addresses and execution sequence pointers, not text names. However, mismatched names cause confusion during system maintenance and code audits.

Why doesn't Siemens automatically rename OB100 runtime groups?

Because multiple blocks from different charts can be merged into a single shared OB100 initialization group to optimize CPU startup performance.

What does 'Optimize Run Sequence' do in the Runtime Editor?

It analyzes block interconnections and rearranges blocks within runtime groups so that upstream block outputs are calculated before downstream block inputs, eliminating 1-cycle calculation delays.