Tracking CFC Chart Changes in PCS7: VXM, Badges, Block Indicators

1. Overview: Why Change Tracking Matters in PCS7 CFC

SIMATIC PCS 7 Continuous Function Charts (CFC) are the primary engineering artifact for the AS 410 / AS 400 controller family. Unlike classic STEP 7 ladder or STL, CFC stores both compiled code and the offline chart topology inside the SIMATIC Manager project tree. When multiple engineers edit the same S7 program, or when a chart is modified after the last successful download, the runtime program in the CPU no longer matches the offline source. PCS 7 will refuse a normal "Download to Target System" and force the user to either re-enable test mode or perform a full download, both of which can disrupt an operating plant if the difference is not understood first.

Siemens ships several built-in indicators in the SIMATIC Manager and the CFC editor so that the engineer can identify, at a glance, which charts have been touched, which blocks inside a chart were modified, and which interconnections have changed. For a deeper, project-wide audit trail the optional SIMATIC Version Cross Manager (VXM) add-on generates an XML image of the program at the moment of a successful download and lets you diff that image against the current project state before the next download.

2. PCS7 Chart State Indicators: The Badge System

From PCS 7 V8.0 SP1 onward, SIMATIC Manager attaches a small visual badge to every chart folder and to every individual CFC chart that reflects the relationship between the offline chart and what is currently in the CPU or in the S7 program container.

The badge is updated by the S7 database the moment the chart is saved in the CFC editor. The badge is not reset by closing and reopening the project; it is only reset by a successful download (or by an explicit "Mark as downloaded" action in some V9.x service packs). This is why, in multi-user or contractor environments, the first thing to check when the dialog "The program on the CPU is different from the offline program" appears is which chart carries the red badge.

2.1 Reading the badges in the component view

1. Open SIMATIC Manager and select the plant view.
2. Navigate to the AS station → S7-Program → Charts.
3. Inspect every chart folder (Unit, Function group, etc.) and expand to the chart level.
4. Right-click a chart with a red badge → Chart > Check consistency to see if the chart will compile before any download attempt.

3. Enabling Test Mode Before Going Online

Before opening an online view of any CFC, PCS 7 requires you to put the CPU into test mode. The test-mode button is the small icon immediately to the right of the Download button on the CFC toolbar (or on the SIMATIC Manager toolbar when the chart is in focus).

1. Open the CFC chart you want to inspect.
2. Click the Test mode icon. A dialog appears: "Do you want to enable CPU test mode?"
3. Click Yes. The CPU enters test mode and the online view becomes available.
4. Click Monitor (on/off) to display live values. The online block view overlays the offline chart, allowing per-block comparison.

If the CPU is already in test mode but the offline chart does not match the CPU, PCS 7 raises the dialog "Register CPU for testing" (German: CPU zum Testen anmelden). This means that an offline change has been made that has not yet been downloaded. The dialog does not block the test-mode request; instead, it warns you that whatever is on the CPU is now potentially out of sync with the offline source, and any monitoring you do will be against the runtime image, not against the current offline chart.

4. Block-Level Change Markers (Red Nubs)

From PCS 7 V9.0 onward, the CFC editor paints the input and output nubs of every block that has been modified, added, or removed since the last download. This is the fastest way to localize a change inside a single chart that contains dozens of blocks.

To use the red nubs in practice:

1. Open the suspect chart.
2. Press F5 or click View > Refresh to force the editor to repaint markers from the current project database.
3. Scan for any red-marked block. Hover the mouse to display a tooltip that includes the timestamp of the last edit and the user account (when Windows authentication is enabled on the project).
4. Open the block's Object properties dialog (→ right-click the block → Object properties) and check the History tab if the project has the Change history option enabled in Options > Customize > Change history.

5. Connection Change Indicators (Cross Arrows)

Modifications to signal interconnections (the lines drawn between output and input nubs) are flagged with a small cross arrow rendered on top of the line. PCS 7 draws three flavors:

• Solid cross on a new line — the interconnection was added since the last download.
• Open cross on a moved endpoint — the line existed but its source or destination block or pin was re-routed.
• Broken cross (red X) — the interconnection was deleted; the line is shown for reference only and is not part of the compiled runtime program.

Combined with the red nubs, the cross arrows let you reconstruct a change list in the form: "Block CTRL_PID_2 has a new input from LIC_101.SP; previous source was LIC_101.PV" without opening the VXM.

6. Version Cross Manager (VXM): The Add-On Solution

For project-wide, file-level diffing, Siemens ships SIMATIC Version Cross Manager (VXM). VXM is an optional add-on package installed from the PCS 7 DVD (or via the SIMATIC PCS 7 installation media) and requires its own license key. The VXM order numbers and the releases that have been GA'd are listed in the Siemens support article SIMATIC Version Cross Manager V8.2 Available for Delivery.

6.1 What VXM compares

VXM walks the entire S7 program container (charts, shared declarations, types, the S7 program itself) and produces a normalized XML representation. It then performs a structural diff and reports:

• Charts added, removed, renamed.
• Blocks added, removed, or re-instanced.
• Block parameter value changes (with old → new value).
• Interconnection add, delete, and modify.
• Compiler / OS / driver changes if those XML sections exist.

7. Configuring VXM: Download Image Generation

By default, PCS 7 does not generate the XML download image because the I/O cost of writing the image slows the full download measurably (a measurable 5-15 % on a typical 2 000-block program). You must opt in.

1. Open a CFC chart.
2. Select Options > Customize → Compile / Download tab.
3. Tick "Generate image of downloaded program for comparison".
4. Click OK. The setting is written to the project registry and applies to all future downloads in that project.

8. VXM Workflow: From Download to Comparison

1. Successful download. After the program is downloaded and the CPU is in RUN, PCS 7 writes an XML image into the project folder under <Project>\<Station>\S7Program\XML (the exact name is configured in the VXM options; default Download.xml).
2. Edit offline. An engineer modifies one or more charts and saves. The S7 program is now out of sync with the XML image.
3. Open VXM. Start the Version Cross Manager from the Windows start menu or from SIMATIC Manager → Tools → Version Cross Manager.
4. Select the comparison pair. Choose File 1 = XML image and File 2 = Current project (S7 program). The online option compares against a fresh snapshot of the CPU.
5. Run the diff. VXM displays a tree view on the left and a detail view on the right. Expand a changed chart → a changed sheet → a changed block to see parameter-level deltas.
6. Export the report. Right-click the result tree → Export → CSV or XML for inclusion in the change-log book of the plant.

8.1 VXM online vs. saved version

VXM has two distinct comparison modes:

• Online check: VXM connects to the AS over the configured PG/PC interface and reads the live program from the CPU. It does not read the XML file in this mode. The online check is what you use to verify that the CPU's running program matches the image you believe is in there.
• Offline check: VXM compares two XML files (typically the previous download image against the current project, or two project archives).

The online check is a read-only operation; it never modifies the project. It is the safe way to confirm a successful download before the second engineer starts work.

9. Archive-Based Comparison Workflow

When VXM is not licensed or when the download image was not generated, you can still perform a useful diff using the PCS 7 archive (.zip) mechanism.

1. At the end of every engineering session, run File → Archive in SIMATIC Manager and store the zip in a versioned directory (V&V\AS410_HVAC_2024-05-12.zip).
2. When a change question arises, open the current project, then File → Retrieve the previous archive to a temporary directory.
3. Open VXM and select File 1 = retrieved project, File 2 = current project.
4. Run the diff. The output is functionally identical to the download-image workflow, but with the disadvantage that the retrieved project temporarily co-exists with the working project; the temporary project must be closed and removed before the engineer continues editing to avoid data loss.

9.1 Using VXM across PCS 7 versions

VXM is generally forward-compatible within a major version (e.g. a V8.2 VXM can read V8.2 SP1 XML). Mixing major versions (V8.2 VXM against a V9.0 XML) is not officially supported; in practice VXM will warn that the schema is unknown and the diff may miss new block types. Always run VXM from a workstation that matches the highest PCS 7 version present in the comparison.

10. Best Practices and Commissioning Tips

• Compile, then archive, then walk away. A compiled-but-archived project is the cheapest insurance against "what changed since lunch".
• Enable the download-image option as soon as the project is commissioned. The 5-15 % download overhead is a small price for a permanent audit trail.
• Use the test-mode button before going online. If PCS 7 asks to register the CPU for testing and the chart carries a red badge, stop and diff before downloading.
• Check the badges weekly. A chronic red badge on a chart that no one claims to have edited usually indicates a project that was edited on a second offline copy and re-merged without a recompile.
• Lock the project for editing with the SIMATIC Logon / Central User Management when the site is large. A locked chart cannot be opened, which prevents accidental concurrent edits and removes the need to diagnose "who changed what" after the fact.
• Keep the VXM license on the FAT workstation. The commissioning engineer is the person most often asking "what is in this chart" and the VXM question travels with the chart.

11. Troubleshooting Matrix

12. FAQ