C135 PCS 7 (PCS7)
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Reconciling Renumbered Driver Blocks (FB400 to FB100) and Splitting Multi-CPU Racks During PCS 7 V6 to V7 Migration

Reconciling Renumbered Driver Blocks (FB400 to FB100) and Splitting Multi-CPU Racks During PCS 7 V6 to V7 Migration

During PCS 7 migration from V6.0 to V7.1, encountering renumbered driver blocks in the Master Data Library (such as OB_BEGIN numbered as FB400 instead of canonical FB100, or PA_AI as FB401 instead of FB101) occurs because older legacy projects permitted custom block numbering before the standardized PCS 7 Basis Library established fixed block number assignments. To resolve this inconsistency, engineers must import the standard V7.1 Basis Library blocks into the Master Data Library, execute 'Update Block Types' to remap chart instances, and clean up obsolete block numbers. Furthermore, when splitting a segmented dual-CPU rack into two independent AS stations, engineers must create a new AS station, copy the CPU and chart hierarchy, assign a dedicated CP 443-1 Ethernet processor to the new controller, and update NetPro connection IDs.

Table of Contents

Executive Summary

Migrating legacy SIMATIC PCS 7 V6.0 automation systems to PCS 7 V7.1 involves resolving architectural and software paradigm shifts. A common complication in long-lived legacy systems is custom block renumbering. In PCS 7 V6.0, system integrators occasionally renumbered standard module drivers—assigning OB_BEGIN to FB400, PA_AI to FB401, or RACK to FB407. When upgrading to PCS 7 V7.1, the new CFC driver generator expects canonical block numbers (FB100 to FB109). Additionally, legacy architectures frequently packed multiple CPUs into a single segmented central rack (e.g. UR2-H split rack 10/8), creating maintenance and engineering bottlenecks. This article provides verified procedures to reconcile block numbering and partition segmented racks into clean, independent automation stations.

Architectural Evolution of Block Numbering: Legacy PCS 7 V6.0 vs Standard V7.1 Basis Library

The evolution of the PCS 7 block library architecture explains why renumbered blocks exist in legacy installations:

  • Legacy PCS 7 V6.0 Approach: Standard technological blocks and module drivers were grouped within a single PCS 7 Library. The engineering system allowed engineers to modify FB numbers freely in the project library to prevent block conflicts with third-party vendor drivers (such as Drive ES or custom telemetry blocks in the FB100-FB200 range).

  • Standardized PCS 7 V7.1 Architecture: Siemens split the system into PCS 7 Library and PCS 7 Basis Library. To ensure deterministic automated driver generation, diagnostic blocks were locked into canonical, standardized numbers:

  • FB100 -> OB_BEGIN

  • FB101 -> PA_AI
  • FB102 -> PA_TOT
  • FB106 -> SUBNET
  • FB107 -> RACK
  • If a project retains legacy FB400-series drivers while the compiler generates standard FB100-series @ charts, the driver generator reports fatal missing block or multi-library version conflicts.

The Risks of Inconsistent Driver Block Numbering During Migration

Attempting to compile a migrated project with mismatched block numbers leads to multiple systemic failures:

  1. Compiler Aborts: The Module Driver Generator expects OB_BEGIN at FB100; if it encounters FB400 with identical symbolic names or interface signatures, compilation halts with Multiple library definitions detected.
  2. OS Compilation Breakdown: WinCC message generation scripts rely on fixed message numbers linked to canonical block types. Renumbered blocks frequently fail to compile alarms into the WinCC Alarm Logging database.
  3. Drive ES Package Conflicts: Classic Step 7 Drive ES packages (e.g. Drive ES V5.3) lack PCS 7 driver wizard integration. Using non-PCS 7 drive packages generates endless compilation warnings and prevents automated faceplate generation.

Step-by-Step Procedure to Standardize Block Numbers via Master Data Library

To reconcile legacy renumbered blocks to canonical V7.1 block numbers cleanly:

  1. Backup Legacy Project: Create a complete archive backup before modifying project libraries.
  2. Open Master Data Library (MDL): In SIMATIC Manager, open the project's Master Data Library.
  3. Import Standard V7.1 Basis Library Blocks:
    * Open File -> Open -> Library -> PCS 7 Basis Library V71.
    * Copy the canonical blocks (FB100, FB101, FB106, FB107, etc.) and paste them into the MDL Blocks folder.
  4. Propagate Canonical Blocks to AS Block Folders:
    * In the Master Data Library Blocks folder, select all updated blocks.
    * Select Options -> Charts -> Update Block Types.
    * Select all target AS stations to push the canonical blocks into the offline block folders.
  5. Update Block Types in CFC Charts:
    * Open a CFC chart in the AS station.
    * Select Options -> Block Types.
    * Move the updated blocks to the Chart Folder and click New Version.
    * Click Clean Up to purge obsolete legacy blocks (FB400, FB401) from the project database.
  6. Full Program Compilation: Execute Chart -> Compile -> Charts as Program (Entire program with module drivers).

Splitting a Multi-CPU Segmented Central Rack into Independent AS Stations

Legacy installations often placed two CPUs into a single segmented rack (such as a 10/8 segmented rack) to share physical space. Splitting this configuration into two independent automation stations substantially improves maintainability:

  1. Create New AS Station: In SIMATIC Manager, right-click the project root and insert a new SIMATIC 400 Station.
  2. Configure Rack and Power Supply: In HW Config of the new AS, place a standard SIMATIC rack (e.g. UR2) and power supply module.
  3. Move CPU and Hierarchy Assignments:
    * Copy the secondary CPU from the old segmented hardware configuration and paste it into the new station's HW Config.
    * Copy the S7 Program container (including Charts and Blocks). Because CFC charts retain internal links to the Plant Hierarchy, copying the entire program folder preserves hierarchy folder assignments.
  4. Delete Secondary CPU from Legacy AS: Remove the secondary CPU and obsolete submodules from the original segmented rack in HW Config.

Communication Architecture: Dedicated CP 443-1 Requirements for Splitted Controllers

When splitting two CPUs from a shared backplane into independent automation stations, communication topology must be updated:

  • The Shared CP Fallacy: In a segmented rack, engineers sometimes routed downloads or communication through a single shared CP or backplane bridge. Once physically separated, each CPU requires its own dedicated communication channel.
  • Dedicated CP 443-1 Processor: The newly created AS station must be equipped with its own CP 443-1 Industrial Ethernet processor.
  • NetPro Connection Reconfiguration:
  • Open NetPro and attach the new CP 443-1 to the plant Industrial Ethernet network.
  • Create dedicated S7 fault-tolerant connections from the new AS to the WinCC OS Server pair.
  • If the two split CPUs communicate peer-to-peer, re-establish S7 connections between them using identical Connection IDs to avoid modifying user communication blocks (BSEND/BRCV).

Legacy Migration and AS Partitioning Decision Matrix

The following table compares block migration strategies and architectural rack partitioning options:

Migration TaskLegacy ConfigurationModernized Target StatePrimary BenefitRequired ActionDriver Block NumberingRenumbered FB400-FB410Standardized FB100-FB109Eliminates driver generator conflictsImport Basis Library V7.1, run Update Block TypesDrive IntegrationClassic Drive ES V5.3 (LAD)Drive ES PCS 7 V7.1 / APLDriver wizard support and OS faceplatesUpgrade to Drive ES PCS 7 block libraryRack ConfigurationSegmented Dual-CPU Rack (10/8)Two Independent AS StationsIndependent shutdown and maintenanceSplit AS in SIMATIC Manager, add dedicated CP 443-1Plant HierarchyMapped across shared ASCleanly segregated by ASClear area-specific WinCC authorizationReconcile Plant View folder assignmentsOS CommunicationShared bus routingIndependent S7 ConnectionsHigher bandwidth, deterministic alarmsRebuild NetPro connections to OS Servers

Verification

To verify successful block renumbering and AS rack splitting:

  1. Check Block Folder Canonical Numbers: Open the AS offline Block folder in SIMATIC Manager. Confirm that OB_BEGIN is FB100, PA_AI is FB101, and legacy FB400-series blocks no longer exist in the container.
  2. CFC Module Driver Generation: Perform an Entire Program CFC compile with Generate module drivers. Confirm that compilation completes with 0 errors and zero duplicate library warnings.
  3. NetPro Connection Test: In NetPro, select the new AS station and verify that S7 connections to OS Servers show valid local/partner endpoints with 0 connection compilation errors.
  4. Online Status Check: Download both AS stations and verify that both controllers transition cleanly to RUN mode with active communication.

Preventive Rules for Master Data Library Maintenance

To maintain pristine library integrity across long-term automation lifecycles:

  • Never Renumber Standard Siemens Blocks: Maintain all standard APL and Basis Library blocks at their factory FB and FC numbers.
  • Use Reserve User Ranges for Custom Blocks: When developing proprietary technological logic, restrict custom FB numbers to user ranges (e.g. FB1000 to FB1999) configured outside the CFC reserved compiler pool.
  • Enforce Centralized Library Distribution: Always modify and store blocks in the central Master Data Library, using Options -> Charts -> Update Block Types to distribute updates deterministically across all plant controllers.

Limitations and Operational Precautions

Splitting an AS station and updating block types alters CPU system data blocks and instance data block interfaces. This migration cannot be downloaded via online delta download; both controllers must undergo full compilation and download in CPU STOP mode.

When sizing new racks, power supplies, CP 443-1 communications processors, and Drive ES PCS 7 software licenses, all components must be validated against official Siemens catalogs and confirmed through an authorized Siemens distributor quotation.

Engineer FAQ

Why did earlier engineers renumber blocks to FB400?

In early PCS 7 V6.x projects, third-party libraries or user logic often occupied lower FB ranges, prompting engineers to manually renumber driver blocks before Siemens standardized the Basis Library.

Can two CPUs in a segmented rack be downloaded independently?

Yes, but they share the same physical rack backplane. A power supply failure or backplane fault stops both CPUs. Splitting them provides full physical isolation.

Does updating block types in CFC alter existing parameter settings?

No. The CFC 'New Version' engine preserves existing pin interconnections, configured constants, and inverted inputs.

Can Drive ES V5.3 blocks generate PCS 7 APL faceplates?

No. Classic Drive ES V5.3 is intended for Step 7 machine automation. Full PCS 7 integration requires the Drive ES PCS 7 library.

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