Auditing and Cleaning Unused Symbols in SIMATIC PCS 7 - Cross-References and Address Overview Tools

In SIMATIC PCS 7, identifying and cleaning unused symbols from the Symbol Table is accomplished using two native diagnostic utilities: the Address Overview in HW Config and the Plan Reference Data in the CFC Editor. In HW Config, selecting View -> Address Overview displays all physical input (I), output (Q), and peripheral addresses allocated to hardware modules. In the CFC Editor, pressing Ctrl+Alt+R (or selecting Options -> Reference Data -> Display) and choosing Cross References -> Plan Element -> Operand generates a complete list of every symbol and memory address actively interconnected within Continuous Function Charts. Comparing the exported Symbol Table against the CFC operand reference data allows engineers to filter and purge obsolete, orphaned symbols safely without risking broken connections.

Symbol Management Architecture in SIMATIC PCS 7

In SIMATIC PCS 7, the Symbol Table (Symbols) in SIMATIC Manager links human-readable tag names (e.g., FIT101_PV, PUMP_START) to raw controller peripheral addresses (IW 512, Q 4.0) and global memory flags (M 10.0). Over years of commissioning, project revisions, and instrumentation changes, symbols are frequently created for signals that are subsequently decommissioned or rewired.

Accumulating hundreds of unused symbols creates confusion for maintenance teams and bloats the engineering database. Because CFC charts utilize symbolic addressing to automatically bind channel driver inputs (Pcs7AnIn.PV_In, Pcs7DiIn.PV_In), engineers must systematically verify whether a symbol is genuinely dormant before deleting it from the project database.

HW Config Address Overview vs CFC Reference Data

Two distinct tools provide complete visibility into hardware allocation and software utilization:

Diagnostic UtilityWhere to AccessInformation ProvidedEngineering PurposeAddress OverviewHW Config -> View -> Address OverviewDisplays all configured module I/O ranges (Inputs, Outputs)Verifies which physical addresses exist in hardware racksCFC Reference DataCFC Editor -> Options -> Reference Data -> Display (Ctrl+Alt+R)Displays all operands actively used across CFC and SFC chartsProves whether a symbol is interconnected in application logicSymbol Table FilterSIMATIC Manager -> Open SymbolsAlphabetical list of all defined symbolic namesAllows exporting and editing symbol definitions

By cross-referencing the Address Overview against the CFC Reference Data, an engineer can instantly identify symbols that reference non-existent hardware or symbols that exist in the dictionary but are never placed onto a chart.

Step-by-Step Procedure to Audit and Purge Unused Symbols

To audit the Symbol Table and remove obsolete entries cleanly, execute the following workflow:

Generate CFC Operand Reference Data: Open any CFC chart. Select Options -> Reference Data -> Display (shortcut Ctrl+Alt+R). In the reference data window, select View -> Cross References Plan Element -> Operand. This lists all inputs, outputs, memory flags, and timers referenced in charts.
Export Used Operands: In the reference data window, select Reference Data -> Export. Save the active operand list as a text/CSV file (Used_Operands.csv).
Export Master Symbol Table: In SIMATIC Manager, navigate to the S7 Program folder. Double-click Symbols. Select Symbol Table -> Export. Save the file as All_Symbols.sdf or .csv.
Reconcile and Identify Orphans: In Microsoft Excel, compare the two lists using a VLOOKUP formula. Any entry present in All_Symbols.csv that does not match an entry in Used_Operands.csv is an unused symbol.
Purge and Re-Import: In the Symbol Table editor, highlight the verified unused symbols and delete them. Save the Symbol Table.
Perform Consistency Check: In the CFC editor, select Chart -> Check Consistency -> Entire Program to confirm that zero active interconnections were broken.

Verification

Verify symbol cleanliness and compilation integrity using these diagnostic checks:

CFC Program Compilation: Execute Chart -> Compile -> Chart as Program -> Scope: Changes Only. Confirm that compilation finishes with 0 Errors and that no missing operand warnings appear.
Driver Generator Execution: Ensure 'Generate module drivers' runs cleanly during compilation, confirming that all channel driver addresses match active hardware.
Symbol Table Re-Check: Re-open the Symbol Table. Verify that total symbol rows match the active I/O count of the plant.

Limitations and Operational Precautions

When cleaning symbol tables, observe these operational precautions:

Unconnected Spare Channels: Field instrumentation designs often reserve 20% spare I/O channels. Spare symbols already wired to terminal blocks should be retained with a descriptive comment (e.g., SPARE_CH_01) rather than deleted.
WinCC Direct Tag Connections: In rare hybrid projects, WinCC tags may read peripheral addresses directly via raw S7 connections without passing through CFC channel drivers. Verify WinCC Tag Management before deleting memory flags.
Backup Prior to Purging: Always create a full Multiproject archive (File -> Archive) before deleting symbols.

Engineer FAQ

Can I filter unused symbols automatically with a single button in STEP 7?

Standard STEP 7 does not have a single-click 'Delete Unused Symbols' button because doing so could accidentally wipe spare hardware symbols or SCADA-only variables. The export-and-compare workflow is the safe industry standard.

Why are some symbols displayed in strikethrough font?

Strikethrough font in the symbol selector indicates a known GUI display bug in STEP 7 V5.6 (fixed in Update 3 / PCS 7 V9.0 SP1), or an address syntax conflict where an address is defined with conflicting data types.

Does an oversized Symbol Table slow down CPU cycle time?

No. The Symbol Table resides exclusively on the Engineering Station hard drive. It is not downloaded to the CPU work memory and has zero impact on PLC scan time.