Tracing Signal Logic and Block Instances Using PCS 7 Chart Reference Data

To trace signal logic, find points of use for I/O addresses (such as Q8.5), or identify which CFC contains a specific FB or FC in SIMATIC PCS 7, use the Chart Reference Data editor. In any open CFC chart, navigate to 'Options -> Chart Reference Data' (or press Ctrl+Alt+R). In the reference data window, select 'View -> Cross-References Chart Element -> Address' to locate physical I/O addresses, or 'Block Types' to display every chart instance of an FB/FC. Right-click the listed record and select 'Go to Point of Use' to navigate directly to the block and interconnected chart logic.

Limitations of Classic STEP 7 Search Tools in PCS 7

Engineers transitioning from discrete STEP 7 (LAD/FBD/STL) to SIMATIC PCS 7 often search for logic by browsing the Blocks folder, opening Organization Blocks (OB1, OB35), or executing standard STEP 7 text searches. In PCS 7, this approach fails because all application software is authored graphically within Continuous Function Chart (CFC) and Sequential Function Chart (SFC) containers.

If an engineer opens a Function Block in the block folder, they may find an output instruction referencing %Q8.5, but STEP 7 cannot indicate which plant unit or CFC chart instantiated that FB. Searching raw text strings across charts is slow and misses dynamic interconnections. The dedicated Chart Reference Data (Plan-Referenzdaten) utility bridges this gap by compiling a comprehensive cross-reference database of all chart elements.

Navigating the Chart Reference Data Toolset

To access and utilize Chart Reference Data:

Open any CFC chart within the target S7 program.
Click Options -> Chart Reference Data or press the keyboard shortcut Ctrl+Alt+R.
The system scans the chart folder and opens the Chart Reference Data management console.
Choose the appropriate diagnostic view from the View menu to interrogate signals, blocks, or execution order.

Tracing Signals, Block Types, and Textual Interconnections

The editor provides specialized views for rapid fault tracing:

Tracing Physical I/O Addresses (View -> Cross-References Chart Element -> Address): Lists all absolute and symbolic I/O addresses (e.g., I8.0, Q8.5, IW512). It details the Chart Name, Block Name, I/O Pin Name, Data Type, and Access Mode (Read or Write). Right-clicking any entry and selecting Go to Point of Use immediately opens the CFC chart and centers the screen on the exact block pin.
Tracing Block Type Utilization (View -> Cross-References Chart Element -> Block Types): Displays every FB and FC present in the project. Expanding a block type (e.g. FB1866 / MotL) enumerates all instantiated blocks across all charts, along with their chart path, instance DB number, and runtime group.
Tracing Textual Interconnections (View -> Cross-References Chart Element -> Textual Interconnections): Identifies unresolved or cross-chart references waiting to be closed.
Evaluating Execution Sequence (View -> Run Sequence): Displays the chronological execution order of runtime groups and blocks across cyclic interrupt OBs (OB30 through OB38).

PCS 7 Execution Model: CFC Runtime Groups vs Classic OB Calling

In traditional STEP 7, the programmer manually writes CALL FB1, DB1 statements inside OB1 or cyclic OBs. In PCS 7, the engineer never writes code directly in Organization Blocks:

Placing an APL block (such as MotL) onto a CFC chart automatically generates an instance DB from the reserved range.
The CFC editor places the block into a default cyclic runtime group (e.g. OB35 with a 100ms cycle).
Interconnecting block outputs to inputs creates software links processed in memory without global bit flags (Merker).
During CFC compilation, the compiler generates the complete OB execution structure and internal call hierarchy automatically.

Chart Reference Data View Matrix and Capabilities

The following table summarizes the diagnostic views available in Chart Reference Data:

View Menu PathTarget DataKey Information DisplayedPrimary Troubleshooting Use CaseCross-References -> AddressAbsolute / Symbolic I/OAddress, Symbol, Chart, Block, Pin, Read/WriteFinding which block drives physical output Q8.5Cross-References -> Block TypesFB, FC, SFC TypesType number, Type name, Instances, Chart, DBFinding where FB is instantiated across plant chartsCross-References -> Chart ElementsAll block pinsBlock, Pin, Value, Interconnection PartnerTracing signal propagation across multiple chartsCross-References -> Textual InterconnectionsString referencesChart, Block, Pin, Target text stringLocating open cross-chart links prior to compilationRun SequenceCyclic OB runtime groupsOB assignment, Group index, Reduction ratio, PhaseDiagnosing execution sequence and deadlocks

[!NOTE]
Commercial Accuracy Notice: Chart Reference Data is an integrated diagnostic utility included in the SIMATIC PCS 7 CFC > engineering software package (6ES7658-1EX58-0YA5). Accessing cross-references and tracing signal logic does not consume > Process Objects or require supplementary engineering licenses.

Verification

Confirm successful logic tracing and signal verification:

Direct Navigation: Select Q8.5 in the Address view, right-click, and select Go to Point of Use. Confirm that the relevant CFC chart opens instantly with the driver or logic block highlighted.
Online Variable Monitoring: Turn on Test -> Test Mode in the resolved CFC chart. Confirm that the output pin evaluates to TRUE (or toggles dynamically) matching the physical field actuator state.
Zero Open Textual Links: Check the Textual Interconnections view. Confirm that no critical signal links remain unconnected (open) prior to commissioning.

Limitations and Operational Precautions

Observe these precautions when using Chart Reference Data:

Reference Data Refresh: If extensive chart edits or block additions were made recently, select Options -> Chart Reference Data -> Update to ensure the cross-reference cache reflects the latest offline state.
Indirect DB Access: If custom legacy blocks access I/O addresses via indirect pointers (e.g. L PIW [AR1, P#0.0]), Chart Reference Data cannot detect the address statically. Standardize on direct CFC signal pins.
Read-Only Inspection: Chart Reference Data is an analytical tool; modifying parameters or addresses must be performed in the source CFC chart, not within the reference table grid.

Engineer FAQ

Why can't I find my output bit (e.g. Q8.5) by searching in SIMATIC Manager?

SIMATIC Manager search scans block comments and discrete STEP 7 code, but does not search inside CFC chart interconnections. Chart Reference Data is specifically designed to index all CFC chart pins and addresses.

Can I call FBs and FCs directly from OB1 in a PCS 7 project?

While technically possible, doing so violates the PCS 7 architecture. Any logic placed outside CFC is invisible to the PCS 7 module driver generator, OS compiler, and delta download manager, risking CPU download locks.

How do I determine which cyclic OB executes a specific block?

Open Chart Reference Data, navigate to 'View -> Run Sequence', and search for the block name. The tree indicates the exact OB (e.g. OB32, OB35) and its execution position within the runtime group.

What is a 'Textual Interconnection' in the cross-reference list?

A textual interconnection is a placeholder link pointing to a chart or pin that does not yet exist or resides in another project. It allows charts to be developed independently before resolving the links centrally.