Customizing CFC Signal Interconnection Colors and Structured Line Display in PCS 7

In SIMATIC PCS 7 CFC, you can customize the display colors of elementary data type interconnections (such as BOOL, REAL, INT, and WORD) via Options > Customize > Colors. However, interconnections for structured data types (STRUCT) and character strings (STRING) are deliberately hardcoded to display as solid black lines and cannot be user-customized. The CFC graphics engine enforces this fixed visual appearance so engineers can instantly differentiate complex structured data highways from elementary scalar process signals.

CFC Interconnection Visual Architecture and Data Type Differentiation

In SIMATIC PCS 7 Continuous Function Chart (CFC), graphical signal lines represent software data exchanges between block inputs and outputs. As plant automation logic scales to thousands of interconnections across multiple charts and runtime groups, visual clarity is critical for commissioning and debugging.

To ensure safety and readability, the CFC graphic subsystem classifies interconnections into distinct visual classes:
* Elementary Data Types: Scalar signals such as BOOL (binary logic), REAL (floating-point process values), TIME, and integer formats (INT, DINT, WORD, DWORD). The CFC editor permits engineers to assign customized colors to these signal types to highlight safety lines, interlocks, or specific technological subsystems.
* Complex / Structured Data Types: Structures (STRUCT, such as APL structures RealVal.Value + RealVal.ST), strings (STRING), and arrays. These contain composite memory allocations and multiple nested sub-elements.
* Chart-to-Chart (Cross-Sheet) Connectors: Signals extending beyond the local sheet boundary, indicated by page references in chart sheet margins.

Configuring CFC Connection Colors and Display Limitations

Engineers can adjust graphical preferences in the CFC editor through the menu Options > Customize > Colors. In this dialog, the user can configure foreground, background, grid, and connection line colors.

However, when an engineer attempts to set all interconnection lines to a uniform color (such as dark blue), the CFC compiler and display manager maintain fixed rendering rules:
1. Lines linking elementary data types update to the selected color.
2. Lines representing STRUCT and STRING variables remain black.
3. Lines representing chart-internal feedback loops or inverted binary inputs maintain dedicated visual identifiers (such as a solid circle for inversion).

This behavior is hardcoded into the Siemens CFC graphic engine (s7cfcapp.exe). It is an intentional design rule rather than a software defect: structured data flows must remain distinct to prevent engineers from mistaking a composite data structure for an elementary boolean or analog value.

Color Customization Support Across CFC Data Types

The following table details the customization options and graphical representations enforced by the PCS 7 CFC editor:

Data Type CategorySpecific Data TypesConfigurable Color in CFC Options?Default Visual AppearanceOperational SignificanceBinary / BooleanBOOLYesThin line (Configurable color)Single-bit process status, interlocks, and commands.Numeric / ScalarREAL, INT, DINTYesThin line (Configurable color)Analog values, setpoints, timers, and counters.Bit StringsBYTE, WORD, DWORDYesThin line (Configurable color)Status words, feature words, and error masks.Structured TypesSTRUCT (APL Structs)No (Hardcoded)Solid black line (Standard thickness)Composite structures carrying process value and Signal Status (ST).Text / StringsSTRINGNo (Hardcoded)Solid black lineText identifiers, unit designations, and message strings.Inverted BinaryBOOL (Inverted)Partial (Line color changes, dot remains)Inversion dot at block pinLogical NOT condition evaluated at the input pin.Global VariablesShared DB / SymbolsYesSheet margin reference boxExternal symbol table or global data block link.

Table 1: Data type color customization matrix in SIMATIC PCS 7 CFC.

Navigating and Tracing Structured Interconnections in Complex CFC Charts

Because structured lines cannot be color-coded, engineers use built-in CFC navigation and documentation tools to trace complex signal routes:

Connector Highlighting: Click directly on the connection line or the connector pin. CFC highlights the entire signal path—including source block pin, routing line, and destination pin—in bright cyan/yellow across the sheet.
Sheet Reference Jumps: Double-click on the margin reference indicator at the edge of the sheet to jump directly to the target chart and block pin.
Signal Tracking Window: Use the Chart > Jump to Partner command (shortcut Ctrl + J) or open the Interconnection List (Options > Interconnections) to view a tabular listing of all inputs and outputs associated with structured types.
CFC Bookmarks: Place bookmarks on critical charts to switch rapidly between master logic and sub-charts.

Verification

To verify CFC color configuration settings:

In SIMATIC Manager, open any CFC chart containing both elementary (REAL / BOOL) and structured (STRUCT / STRING) connections.
Navigate to Options > Customize > Colors.
Under the Connections category, select a distinctive color (e.g., Blue or Red) and click OK.
Observe the chart canvas:
* Verify that scalar interconnections (BOOL, REAL) immediately render in the selected color.
* Verify that structured interconnections (STRUCT, STRING) remain black.
Click on a structured connection line: verify that the interactive selection highlight color activates correctly across the entire route.

Limitations and Operational Precautions

Do not attempt to modify binary .ini files or DLL resources of the STEP 7 / CFC installation to alter hardcoded struct line colors; doing so can corrupt the CFC editor and invalidate software licensing.
Be cautious when setting custom line colors that closely match the sheet background or the text color, as low contrast can cause errors during code review and commissioning.
Exporting CFC charts to PDF or printing maintains the hardcoded black lines for STRUCT connections regardless of printer color profiles.

Engineer FAQ

Can I change the thickness of structured connection lines in CFC?

No. The line thickness and styling for structured types are fixed by the CFC rendering engine to ensure consistent visual presentation across all engineering stations.

Why does APL use STRUCT for almost all process values?

The Advanced Process Library (APL) uses structured types (such as Struct: Value + ST) to transport both the process value and its IEEE 754 quality code (Signal Status) simultaneously across a single interconnection line.

Does changing CFC colors affect controller execution or compilation?

No. CFC display colors are purely local graphical editor settings stored in the user profile. They have zero impact on controller program execution, compilation checksums, or CPU cycle time.