Tracing Variable Usage in SIMATIC PCS 7 SFC Types - Cross-Reference and Step-Transition Access Analysis

In SIMATIC PCS 7 Sequential Function Chart (SFC) engineering, tracing where specific block contacts, technological inputs, or internal flags are read or written across complex SFC Types containing dozens of steps and transitions cannot be efficiently performed by manual visual inspection. Instead, engineers must use the built-in SFC Cross-Reference utility accessible via the STEP 7 Reference Data tool ('Options > Reference Data > Display' in SIMATIC Manager) by selecting 'View > Accesses in SFC Types'. This dedicated matrix view lists every variable, parameter, and block I/O used within the SFC Type, explicitly identifying the step name, transition name, and whether the variable undergoes read or write access.

Challenges of Variable Tracking in Large SFC Types

In SIMATIC PCS 7, Sequential Function Chart (SFC) Types define state-based sequential logic for equipment phases (such as reactors, dryers, and CIP skids). A comprehensive SFC Type can easily encompass 50 to 100 sequential steps and transitions:
- Steps: Execute initialization actions, target setpoint assignments, valve commands, and motor start triggers.
- Transitions: Evaluate process conditions, interlocks, feedback run signals, and timer completions to advance the state machine.

When an engineer needs to determine where a specific technological input (e.g., SafeInterlock or Temp_High_Trip) is utilized, manually clicking through 100 step property tabs and transition condition dialogs is error-prone and time-consuming. In classic STEP 7 ladder/FBD editors, shortcuts like Ctrl+Alt+F open the cross-reference list. In PCS 7, an equivalent, specialized tool exists specifically for SFC Types.

The SFC Type Cross-Reference Engine ('Accesses in SFC Types')

The Reference Data processor in SIMATIC Manager includes a dedicated parser engineered specifically for SFC Types and SFC instances:
- Comprehensive Variable Scope: It indexes all inputs, outputs, technological parameters, and internal flags declared in the SFC Type interface.
- Location Pinpointing: For every variable reference, it identifies the exact topological location:
- SFC Type name.
- Step name (e.g., S_Heat_Up).
- Transition name (e.g., T_Temp_Reached).
- Action execution phase: Initialization action, Processing action, or Termination action.
- Access Mode Identification: Clearly differentiates between Read Access (variable evaluated in a transition condition or step comparison) and Write Access (variable assigned or set in a step action).

Step-by-Step Procedure: Tracing Variables in SFC Types

Follow this procedure to locate and trace variable accesses inside any SFC Type:

Step 1: Open the Reference Data Window in SIMATIC Manager

In SIMATIC Manager, select the Charts folder in the target S7 Program.
Select menu Options > Reference Data > Display.
If prompted to generate reference data, select Yes to ensure the latest compiled database is evaluated.

Step 2: Open the 'Accesses in SFC Types' View

In the newly opened Display Reference Data window, click the top menu: View > Accesses in SFC Types.
A comprehensive tabular matrix is displayed containing columns:
- SFC Type
- Object / Step / Transition
- Variable / Address
- Access Type (Read / Write)
- Action Type (Initialization / Cyclic / Termination)

Step 3: Filter and Search for the Target Signal

Press Ctrl+F to open the search bar, or use the column filter buttons.
Enter the variable name (e.g., In_Agitator_Running or CFC_Block.Out).
The table filters down to show every step where the variable is assigned and every transition where it is tested as a condition.
Double-click any row to jump directly to that step or transition within the SFC Editor.

Comparative Matrix: Variable Tracing Methods in PCS 7

The table below compares methods for tracing variables within PCS 7 sequential logic:

Diagnostic MethodSpeedCompletenessIdentifies Read vs WriteDirect NavigationManual Step InspectionExtremely Slow (Hours)High risk of missed stepsManual deductionNoSFC Search Function (Ctrl+F)ModerateShows occurrences in active chartPartialSteps sequentiallyAccesses in SFC Types (XRef)Instantaneous100% ComprehensiveExplicit Read/Write ColumnDouble-click jumpProcess Object View (POV)Fast for parametersParameters only (Not transition logic)N/AOpens chart

Verification

To confirm that variable references in an SFC Type are correctly traced and validated:
1. Cross-Reference Navigation Test: In the 'Accesses in SFC Types' table, double-click a listed step; verify that the SFC Editor opens immediately with the target step properties dialog active.
2. Logic Consistency Check: Confirm that output control variables written in initialization steps are cleanly reset or terminated in the corresponding step termination action.
3. SFC Type Compilation: In the SFC Editor, select Options > Compile...; verify that the compiler logs 0 errors and 0 warnings regarding uninitialized variables.

Limitations and Operational Precautions

Engineering teams must observe the following precautions:
- Reference Data must be regenerated following any logic modification; viewing outdated reference data can cause engineers to overlook newly added variable references.
- Writing to the same external block parameter from multiple concurrent SFC steps can create race conditions; always inspect cross-reference write occurrences to ensure mutual exclusion.
- Modifying SFC Type interfaces requires updating all instantiated SFC instances in the plant hierarchy; always perform type-instance synchronization following variable restructuring.

Engineer FAQ

Can I see cross-references for individual SFC instances (not types)?

Yes. In the Reference Data window, select 'View > Block Interconnections' or 'Accesses in SFC' to trace variable accesses across instantiated SFC charts.

Can I print or export the SFC cross-reference list to Excel?

Yes. In the Display Reference Data window, select 'File > Export...' to save the entire table as a CSV or text file for validation and design documentation.

Why is 'Accesses in SFC Types' greyed out in Reference Data?

The option is greyed out if the project contains no SFC Types (only standard SFC charts), or if the project has not been compiled since SFC Types were added.