C135 PCS 7 (PCS7)
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Replacing S7-400H Controller Hardware (417-4H to 417-5H) in HW Config and NetPro Without Data Loss in PCS 7

Replacing S7-400H Controller Hardware (417-4H to 417-5H) in HW Config and NetPro Without Data Loss in PCS 7

Replacing a misconfigured or upgraded S7-400H CPU (such as transitioning from 6ES7417-4HT14-0AB0 to 6ES7417-5HT06-0AB0) in SIMATIC PCS 7 HW Config is executed cleanly using the 'Replace Object...' context menu command. This function preserves existing I/O module assignments, subnets, and addresses while mapping CPU parameter structures. However, engineers must meticulously verify memory allocation profiles, process-image partition (PIP/TPA) assignments, and re-establish S7 communication connections in NetPro. Following hardware replacement, engineers must compile HW Config, compile NetPro, execute an Entire Program CFC compile with module drivers, and perform a full download in CPU STOP mode during a planned maintenance window.

Table of Contents

Executive Summary

In high-availability SIMATIC PCS 7 process plants, maintaining exact synchronization between the physical automation controller hardware and the STEP 7 HW Config hardware database is mandatory. A critical engineering discrepancy arises when an automation station is physically upgraded or inadvertently configured with a legacy controller model—such as configuring an older CPU 417-4H (6ES7417-4HT14-0AB0) in HW Config while the physical rack contains the modern high-performance CPU 417-5H (6ES7417-5HT06-0AB0). This mismatch prevents establishing new high-speed S7 fault-tolerant communication links in NetPro and can cause diagnostic faults. This technical article explains how to safely swap the CPU object in HW Config, preserve complex network connections and chart assignments, and execute a verified transition without application logic loss.

Hardware Architecture: CPU 417-4H vs CPU 417-5H Technological Enhancements

Understanding the architectural evolution between S7-400H generations is essential before performing hardware exchanges:

  • SIMATIC CPU 417-4H (V4.x Generation): Features 30 MB total work memory (15 MB code / 15 MB data), integrated PROFIBUS DP interfaces, and relies on external pluggable sync submodules operating over dedicated fiber optic cables.
  • SIMATIC CPU 417-5H (V6.0 Generation): Features 32 MB integrated work memory (split dynamically), high-performance processing cores with substantially lower instruction execution times, integrated PROFINET IO interfaces (2-port switch), enhanced diagnostic buffers, and faster redundancy failover times (typically under 50 ms).
  • Parameter Retention Differences: Because the internal parameter structure and memory allocation algorithms differ across generations, a blind hardware swap without reviewing CPU properties risks exhausting configured cyclic interrupt partitions.

The 'Replace Object' Command Mechanics in HW Config

Rather than deleting the CPU from the central rack (which destroys all assigned subnets, I/O module addresses, and program links), STEP 7 provides the 'Replace Object...' (Objekt tauschen...) workflow:

  1. Context Menu Execution: Right-clicking the CPU in Slot 3/4 of Rack 0 (and Rack 1 in redundant systems) and selecting Replace Object... opens the compatible hardware selection catalog.
  2. Catalog Mapping: Selecting the target MLFB 6ES7417-5HT06-0AB0 prompts the configuration engine to migrate existing parameters.
  3. Parameter Adoption: All compatible settings—including MPI/DP addresses, rack position, and diagnostic interrupt OB assignments—are automatically adopted by the new module.
  4. Connection Reassignment: A dialog prompts the engineer to confirm reassignment of existing communication endpoints.

Preserving NetPro S7 Connections and Process-Image Partitions

Replacing the CPU object impacts two critical architectural subsystems:

  • Process-Image Partitions (PIP / TPA): The CPU 417-5H supports different process-image update cycles. Verify that all configured OB execution groups (OB30 to OB38) remain correctly mapped to their respective process-image partitions in CPU Properties under the Cycle/Clock Memory tab.
  • NetPro S7 Fault-Tolerant Connections: S7 connections to WinCC OS Servers, BATCH servers, and partner AS controllers reference the CPU's internal communication interface IDs. Replacing the CPU requires opening NetPro to verify that S7 connections remain linked to the correct local endpoints and recompiling all connections.

Step-by-Step Procedure for Live CPU Hardware Reconfiguration

To replace the CPU in HW Config and download to the controller cleanly:

  1. Document Existing Parameters: Open the current CPU properties in HW Config. Capture screenshots of the Memory, Cycle/Clock Memory, Diagnostics/Clock, and Protection tabs.
  2. Execute Replace Object in HW Config:
    * In HW Config, right-click the existing CPU 417-4H and select Replace Object....
    * Select 6ES7417-5HT06-0AB0 with the matching physical firmware version (e.g. V6.0).
    * Accept the replacement prompt. Repeat for the partner CPU in Rack 1 for redundant S7-400H systems.
  3. Configure Redundancy Sync Modules: Insert matching sync submodules (e.g. 6ES7960-1AA06-0XA0) into the sub-slots of the 417-5H.
  4. Reconcile CPU Object Properties: Open Object Properties for the new CPU. Verify memory partitions, PIP assignments, and maximum communication jobs against the documented baseline.
  5. Save and Compile HW Config: Execute Station -> Save and Compile.
  6. Verify and Compile NetPro: Open NetPro, select the station, click Network -> Save and Compile, selecting Compile and check everything.
  7. Compile CFC Charts: In SIMATIC Manager, select the Chart container and click Chart -> Compile -> Charts as Program. Select Entire program with Generate module drivers checked.

Controller Replacement and Network Migration Matrix

The following table summarizes parameters, risks, and required checks when swapping S7-400H CPU objects:

Engineering ItemLegacy Model (417-4H)Upgraded Model (417-5H)Impact on MigrationVerification ActionSiemens MLFB6ES7417-4HT14-0AB06ES7417-5HT06-0AB0Physical hardware changeValidate exact part number on CPU faceplateWork Memory30 MB (15 MB Code / 15 MB Data)32 MB IntegratedMemory boundary increasesCheck Memory tab in Module InformationSync SubmodulesV4 Sync modulesV6 Sync modules (6ES7960-1AA06-0XA0)Incompatible hardwareMust replace optical sync submodulesNetPro S7 ConnectionsBound to V4 CPU interfaceMust rebind to V6 interfaceCommunication link break if uncompiledRecompile NetPro (Check Everything)Download ModeDelta download blockedInitial STOP mode requiredPlant production impactExecute during scheduled turnaround window

Verification

To verify that the CPU replacement has been executed successfully:

  1. Online Hardware Diagnostic Check: Connect online via SIMATIC Manager and open Module Information (Ctrl + D). Confirm that the online CPU order number reads 6ES7417-5HT06-0AB0 and firmware version matches offline configuration.
  2. Redundancy Synchronization (Redundant Systems): Verify that both CPUs enter RUN mode and the REDF (Redundancy Fault) LED turns OFF. Confirm the diagnostic buffer displays 'Event ID 16#4304: Redundant mode started'.
  3. NetPro Connection Status: In NetPro, establish an online connection and confirm that all S7 connections to WinCC OS Servers and peer controllers indicate Active/Established (green status).
  4. OS Alarming and Faceplate Control: Open WinCC Runtime on an OS Client. Verify that live analog values update dynamically and faceplate operator commands execute without latency.

Download Sequence and Redundancy Synchronization Precautions

When downloading hardware changes of this magnitude:

  • Full Stop Requirement: Exchanging a CPU type in HW Config fundamentally alters the system data blocks (SDBs). This change cannot be downloaded via online delta download. The CPU (or both CPUs in a redundant pair) must be transitioned to STOP mode.
  • Sequential Download Sequence:
    1. Download Hardware Configuration in STOP mode.
    2. Download NetPro connections in STOP mode.
    3. Download AS Program (Entire Program) in STOP mode.
    4. Warm restart the primary CPU, followed by coupling and redundancy synchronization of the standby CPU.

Limitations and Operational Precautions

Never attempt to perform an online CPU replacement while the plant is actively processing live volatile materials without scheduled downtime. Redundancy coupling between a 417-4H and a 417-5H is technically impossible; both racks must use identical CPU models.

When purchasing S7-400H CPUs, sync submodules, fiber-optic patch cables, or memory cards, all hardware MLFBs must be validated against official Siemens catalogs and confirmed through an authorized Siemens distributor quotation.

Engineer FAQ

Can I replace the CPU in HW Config by deleting the old one and inserting the new one?

Do not delete the old CPU. Deleting the CPU deletes all program links, chart assignments, and NetPro connections. Always use 'Replace Object...' to preserve configuration data.

Can a CPU 417-4H and CPU 417-5H run together in a redundant pair?

No. Redundant S7-400H pairs require identical CPU MLFBs, identical firmware revisions, and identical memory card configurations.

Will my CFC chart logic be modified when swapping the CPU?

No. CFC charts, blocks, and technological logic remain completely unchanged, although an Entire Program compilation is required to generate new hardware drivers.

Can the old fiber-optic sync modules from a 417-4H be used in a 417-5H?

No. The CPU 417-5H requires V6 sync submodules (e.g. 6ES7960-1AA06-0XA0); older V4 sync modules will not be recognized by the CPU.

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