Automated Function Block Replacement in SIMATIC PCS 7 CFC: Tools, Workflows, and Block Type Import Mechanics

In SIMATIC PCS 7 Continuous Function Chart (CFC), there is no single-click native command that automatically converts or swaps one block type for a completely different technological block type across all charts (e.g. converting classic CH_AI to APL Pcs7AnIn). However, when updating identical block types to newer library versions, CFC provides the automated 'Update Block Types' function (Options -> Block Types), which upgrades instances across all charts while retaining interconnections. For replacing disparate block types automatically, engineers utilize the Import/Export Assistant (IEA), Process Automation Accelerator (PAA), or exported CFC XML/CAx transformation scripts.

Block Type Mechanics in SIMATIC PCS 7: Types vs Instances

SIMATIC PCS 7 relies on a strict object-oriented architecture in Continuous Function Chart (CFC). Technological functions are authored as Block Types (stored as FBs/FCs in the Master Data Library). When placed onto a CFC chart, the system creates a Block Instance backed by an allocated Data Block (DB) and chart interconnection metadata.

Engineers frequently seek automated methods to replace blocks—either when upgrading a project to a newer library release or when attempting to modernize legacy software by replacing obsolete channel drivers or classic blocks with modern Advanced Process Library (APL) blocks.

Updating Identical Block Types: The Native 'Update Block Types' Mechanism

When upgrading a block to a newer revision of the same block type (e.g. updating MotL from APL V8.1 to V8.2, where block name and FB number match):

Open any CFC chart in SIMATIC Manager.
Select Options -> Block Types....
Select the block in the project chart folder and click New Version... (or copy the new FB from the Master Data Library into the block folder).
CFC prompts to run Update Block Types.
The compiler scans all charts across the entire CPU, updates the internal interface, preserves all existing signal interconnections and parameter values, and updates block instances automatically without manual chart editing.

Why Replacing Different Block Types Cannot Be Done Directly in CFC

A completely different challenge arises when attempting to replace different block types (e.g. replacing classic CH_AI [FB33] with APL Pcs7AnIn [FB1869]):

Interface Divergence: The input/output pin definitions, data types, and structures differ fundamentally. Classic CH_AI outputs raw V and QBAD, whereas APL Pcs7AnIn outputs an APL structured variable Out.Value and Out.ST (Signal Status byte).
Semantic Disconnect: CFC cannot arbitrarily guess how dissimilar pins map to one another. Deleting the old block breaks all chart connections, which is why a raw automated 'replace block X with block Y' command does not exist natively in the basic CFC editor.

Automated Bulk Replacement Strategies: IEA, CMT, and PAA

To replace dissimilar blocks automatically across hundreds of charts, engineering workflows deploy advanced automation tools:

Control Module Types (CMT) & Technological IO (TecIO): In PCS 7 V8.1 and V9.0, instances generated from CMTs can be updated globally by altering the master CMT type in the Master Data Library and synchronizing across the project.
Import/Export Assistant (IEA): Generates process tag import/export files (*.pie). Engineers export chart parameters to Microsoft Excel, substitute block references using formulas, and re-import.
Plant Automation Accelerator (PAA) / COMOS: Provides rule-based algorithmic migration engines that parse legacy charts, replace classic blocks with APL blocks, and reconnect signal wires automatically based on predefined mapping rules.

Comparative Block Replacement and Migration Methodology Matrix

The following table compares methodologies for updating and replacing blocks in PCS 7:

Engineering ObjectiveSoftware ToolAutomation DegreeInterconnection RetentionApplicable ScenarioUpdate Same Block Type (Version upgrade)CFC: Options -> Block Types100% AutomatedFully RetainedLibrary service pack updates (e.g. APL V8.1 -> V8.2)Replace Dissimilar Types via CMTType/Instance Synchronization100% AutomatedManaged via CMT rulesStandardized CMT-based plantsBulk Parameter/Signal Re-assignmentImport/Export Assistant (IEA)Semi-Automated (Excel)Mapped via import fileLegacy standard library parameter mass editsFull Classic-to-APL MigrationPlant Automation Accelerator (PAA)Highly AutomatedRule-based rewireModernization of massive legacy plantsManual Chart EditingCFC EditorManualWires broken upon deletionSmall projects (< 50 charts)

Step-by-Step Procedure to Update Block Types Across Multiprojects

To execute a safe, automated update of identical block types:

Backup Multiproject: Create an archive of the entire multiproject via SIMATIC Manager.
Update Master Data Library: Copy the latest block versions from the updated library (e.g. PCS 7 APL V8.2) into the project's Master Data Library.
Open Block Types Dialog: Open any CFC chart -> Options -> Block Types.
Execute Block Update: Select the target blocks in the Chart folder pane, click Update Block Types....
Select Target S7 Programs: Check all AS controllers in the multiproject to receive the updated block type.
Review Log: Inspect the update log. Confirm that parameters, messages, and interconnected signals are retained.
Compile Charts: Perform Compile Charts as Program -> Changes Only to verify compatibility with online CPU changes.

Verification

Verify block replacement health through these steps:

CFC Interface Verification: Open updated charts. Confirm new pins are visible and existing interconnections remain intact without red breaks.
Block Consistency Check: In SIMATIC Manager, run Options -> Check Block Consistency. Confirm zero interface mismatches.
Online Download Test: In CFC, execute Download -> Changes. Confirm changes download without requiring a CPU STOP.
Runtime Diagnostics: Confirm block icons in WinCC continue updating live process values without quality faults.

Limitations and Operational Precautions

Observe the following migration safeguards:

CPU Stop Risk during Block Updates: If a block type update alters existing parameter data types or adds parameters between existing variables, the DB structure shifts, which can prevent a 'Changes Only' download and force a full CPU STOP download.
Commercial Accuracy Disclaimer: Software order numbers (MLFBs), package structures, and hardware capacity prerequisites vary across PCS 7 versions and hardware platforms. System integrators must confirm exact software entitlements and licensing requirements against the official Siemens Catalog CA 01 and obtain an authorized Siemens distributor quotation prior to purchasing.

Engineer FAQ

Can updating block types force a CPU STOP during download?

Yes. If the block update alters internal data structures or variable order in the instance DB, a delta download is rejected, requiring a full download with CPU STOP.