Identifying Unused Symbols and Orphaned I/O Addresses in SIMATIC PCS 7

In SIMATIC PCS 7, identifying unused symbolic names and orphaned I/O addresses after extensive modifications requires using the Cross-Reference (XRef) tool or the Process Object View Signals table. In SIMATIC Manager, navigate to Options > Reference Data > Display and select 'Symbols Without Addresses / Addresses Without Symbols' to list unused symbols in classic S7 logic. For PCS 7 channel drivers in CFC, export the Signals table from Process Object View to Microsoft Excel, compare it against the exported Symbol Table, and identify unreferenced field sensors.

Symbol Management and I/O Binding in SIMATIC PCS 7

During the lifecycle of a SIMATIC PCS 7 automation project, extensive instrument changes, hardware replacements, and functional redesigns frequently leave behind unused symbols in the STEP 7 Symbol Table.

In standard STEP 7 Classic, symbols link physical peripheral addresses (e.g., IW512, Q4.0) to symbolic identifiers. However, in SIMATIC PCS 7:
* Physical I/O addresses are not accessed directly in CFC logic.
* Instead, symbols are interconnected to the technological input/output pins of PCS 7 channel driver blocks (Pcs7AnIn, Pcs7DiIn, Pcs7AnOu, Pcs7DiOu).
* The PCS 7 Driver Generator (Generate Module Drivers) scans these symbolic interconnections to automatically build the diagnostic hardware tree (MOD_D1, MOD_HA).
* Orphaned symbols clutter engineering documentation, confuse maintenance technicians, and can lead to incorrect signal assignments during future expansions.

Using Reference Data: Symbols Without Addresses Filter

The native STEP 7 reference data engine provides built-in auditing filters:

In SIMATIC Manager, select the S7 Program folder.
Select Options > Reference Data > Generate to rebuild cross-reference databases.
Select Options > Reference Data > Display.
In the view selection window, choose:
* Symbols without Addresses: Displays symbolic tags declared in the Symbol Table that have no corresponding absolute address.
* Addresses without Symbols: Displays raw absolute addresses used in program logic that have no symbolic definition.
* Unreferenced Symbols: Displays declared symbols that are never accessed by any block, chart, or variable table.
While this method identifies orphaned symbols in classic FC/FB code, symbols connected exclusively to CFC channel driver pins may appear as 'unreferenced' in classic XRef if CFC chart reference data is not fully compiled.

Auditing PCS 7 Channel Drivers via Process Object View Signals Table

The standard and most reliable method for PCS 7 environments is auditing the Signals table inside Process Object View:

Audit LayerEngineering LocationScope of InspectionOutput FormatSymbol TableSIMATIC Manager > SymbolsAll project symbolic identifiersExportable SDF/CSV tablePO View Signals TableProcess Object View > SignalsActive I/O signals linked to CFC driver pins (PV_In, PV_Out)Filterable tabular gridPO View ParametersProcess Object View > ParametersAll block pins with interconnection pathsDetailed parameter matrixHW Config AddressesHW Config > Address OverviewAll configured I/O module byte rangesHardware address map

Table 1: Engineering views used to audit I/O assignments in PCS 7.

Automated Excel Cross-Referencing Workflow

To identify every unassigned symbol with 100% precision:

Export Symbol Table:
* Open the Symbol Table in SIMATIC Manager.
* Select Symbol Table > Export. Choose format Data Interchange Format (*.DIF) or ASCII (.SDF / .CSV).
Export PO View Signals:
* In SIMATIC Manager, select the top-level plant hierarchy folder and open Process Object View.
* Switch to the Signals tab.
* Select all rows, right-click, and select Copy.
Compare in Microsoft Excel:
* Paste both datasets into separate tabs of an Excel workbook: Tab_Symbols and Tab_UsedSignals.
* In Tab_Symbols, add a verification formula using COUNTIF:
excel =IF(COUNTIF(Tab_UsedSignals!A:A, A2)=0, "UNUSED / ORPHAN", "ACTIVE")
* Filter on "UNUSED / ORPHAN": the resulting list contains all symbols present in the project that are not connected to any CFC channel driver.
Clean Up Project Database:
* Review the orphaned list with process engineers.
* Delete obsolete symbols from the Symbol Table to prevent future engineering confusion.

Verification

To confirm that unused symbols have been audited and eliminated:

Re-open the Symbol Table in SIMATIC Manager: verify that confirmed obsolete symbols have been removed.
In SIMATIC Manager, execute Options > Reference Data > Generate.
Inspect Unreferenced Symbols: verify that the count of orphaned tags matches project expectations.
Compile CFC charts with Generate Module Drivers: confirm that compilation completes with zero warnings regarding missing hardware addresses or orphaned signal interconnections.

Limitations and Operational Precautions

Never delete symbols assigned to spare I/O channels reserved for future plant expansion without confirming the equipment schedule with the site lead.
Before deleting symbols, verify whether external systems (such as WinCC Tag Management via OPC or third-party SCADA) access symbols via direct absolute addressing.
Always capture a full multiproject backup (File > Archive) before performing bulk symbol deletions.

Engineer FAQ

Can I delete unused symbols while the plant is operating?

Yes. The Symbol Table is an engineering-level naming dictionary; deleting unused symbols that are not connected to active CFC logic does not impact controller execution or require a CPU stop.

Why do some active CFC signals appear as 'unreferenced' in classic XRef?

If CFC charts are compiled using the 'Generate Module Drivers' option, some channel driver connections are dynamically compiled into system blocks (MOD_D1) rather than classic absolute references, which classic XRef may overlook.

Can I reassign an active symbol to a different address directly in PO View?

Yes. In Process Object View (Signals tab), you can modify the signal address directly; PCS 7 automatically updates both the Symbol Table and the CFC chart pin.