Optimizing SIMATIC Version Cross Manager (VXM) Comparisons for Third-Party GSD Hardware

SIMATIC Version Cross Manager (VXM) flags third-party GSD and GSDML I/O devices as entirely different when GSD file revisions, order number strings, or hexadecimal User_Prm_Data parameter sequences differ between engineering workstations. To eliminate false-positive hardware mismatches, install identical GSD/GSDML library versions across both project environments, compile hardware configurations completely, and apply targeted VXM comparison filters.

VXM Hardware Comparison Challenges with Third-Party Slaves

In regulated process automation industries (pharmaceutical, chemical, nuclear), validating hardware and software modifications between project revisions is a mandatory lifecycle requirement. Engineers deploy SIMATIC Version Cross Manager (VXM) to generate regulatory difference logs comparing two PCS 7 multiprojects or project archives.

When evaluating projects containing third-party fieldbus devices—such as R. STAHL IS1 Remote I/O, Pepperl+Fuchs remote interfaces, or Turck PROFIBUS DP/PROFINET stations—VXM frequently flags all third-party I/O modules as completely modified or deleted/re-added, even when no physical parameters, addresses, or channels were changed.

This creates extensive false-positive discrepancies in compliance documentation, forcing engineering teams to perform laborious manual verifications across thousands of I/O points.

Root Cause Analysis: GSD Hexadecimal Parameter Serialization

The root cause of false-positive discrepancies in VXM stems from how STEP 7 HW Config serializes third-party device descriptions:

Standard Siemens Modules vs. GSD Modules:
* Native Siemens modules (e.g. ET 200M, ET 200SP) are defined via internal STEP 7 Object Managers (OM). Their configuration parameters are stored as structured, named XML attributes (e.g. WireBreakCheck = TRUE, MeasuringRange = 4..20mA). VXM compares these discrete semantic fields directly.
* Third-party devices are integrated via Generic Station Description (GSD) or GSDML files. STEP 7 packages third-party module configurations into raw hexadecimal byte streams (User_Prm_Data).
GSD Revision and Date Stamp Discrepancies:
* If Project A was compiled on an engineering station containing GSD revision v1.2 (2014-05-10) and Project B is compared using GSD revision v1.3 (2015-08-20), the internal checksums, module identifiers, and GSD header strings differ. VXM interprets the modules as completely distinct hardware types.
Hex Parameter Byte Padding and Ordering:
* Depending on the sequence in which modules were inserted into the virtual backplane rack, STEP 7 compiles the raw parameter string (User_Prm_Data_Len and parameter bytes). If byte padding or non-essential default values are serialized in differing byte orders, binary comparison fails even though physical device operation is identical.
Missing Hardware Updates in Local Catalog:
* If the comparing station does not have the vendor-specific GSD installed in its local catalog (<Step7Path>\\S7DATA\\GSD), STEP 7 reconstructs the device from cached project data without descriptor metadata, causing VXM to report missing device profiles.

Standardized Remediation and Comparison Workflow

1. Synchronize GSD and GSDML Libraries

On the source engineering PC, locate all third-party GSD files in the project.
In STEP 7 HW Config, select Options > Install GSD Files....
Point to the vendor device library directory (e.g. R. STAHL IS1 device package).
Ensure the identical GSD file versions (same file name, date, and revision) are installed on both the baseline and comparison engineering stations.
In HW Config, execute Options > Update Catalog.

2. Perform Full Hardware Compilation

Open the HW Config station in the baseline project.
Execute Station > Save and Compile.
Open the HW Config station in the target/modified project and execute Station > Save and Compile.
Both stations must be compiled with the identical version of STEP 7 and the same installed Hotfix/Service Pack level to guarantee consistent binary serialization.

3. Configure VXM Comparison Filters

Launch SIMATIC Version Cross Manager.
Select Options > Settings > Comparison.
In the Filter rules tab:
* Disable comparison of graphical coordinates and visual layout attributes.
* Enable attribute filtering for non-functional slave metadata.
Execute the comparison between Project 1 and Project 2.

4. Alternative Textual Diff Workflow for Regulated Validation

If VXM continues to report false-positive hexadecimal differences on third-party hardware:
1. In HW Config, open Station 1 and select Station > Export....
2. Save the hardware configuration as a text file (Station_Baseline.cfg).
3. Open Station 2 and select Station > Export... (Station_Modified.cfg).
4. Compare the two .cfg files using a professional diff utility (such as WinMerge or Beyond Compare). The text .cfg format isolates slot allocations, I/O addresses, and symbolic names clearly from binary driver blobs.

Hardware Comparison Tool Matrix and Feature Scope

Tool / MethodPrimary Comparison TargetThird-Party GSD SupportAudit Trail ComplianceStrengths / LimitationsSIMATIC VXMMultiproject (AS, OS, HW, CFC, SFC)Supported via GSD parserHigh (FDA 21 CFR Part 11 compliant logs)Comprehensive project scope; sensitive to GSD revision shiftsHW Config CompareHardware Stations (HW-Config)Native comparison engineModerate (interactive window only)Fast online/offline or station-to-station check; no PDF exportStation Text Export (.cfg)ASCII Hardware Station ScriptUniversal (ASCII text)High when paired with version controlIsolates actual address/parameter changes from binary metadataSIMATIC XML CompareSTEP 7 Openness XML dumpsFull XML schemaHighAutomated CI/CD integration; requires Openness scripting

Verification

Run VXM comparison between the baseline and revised projects.
Expand the HW Config tree under the target controller.
Verify that unchanged third-party remote I/O racks (e.g. Stahl IS1 nodes) display as identical (black text / no difference icons).
Introduce a deliberate change on Channel 0 of Slot 4 (e.g., change 4-20 mA to 0-20 mA).
Re-run VXM; verify that only Slot 4 Channel 0 is highlighted as modified, with all other slots marked identical.

Limitations and Operational Precautions

Firmware Version Parity: Upgrading a third-party head module firmware in HW Config requires replacing the module in the virtual rack, which inherently registers as a hardware change in VXM.
Master Catalog Dependencies: Never copy project archives between engineering stations without transferring and installing the corresponding third-party GSD files. Opening HW Config without the original GSD installed can corrupt device parameters upon saving.
Regulatory Record Keeping: When presenting comparison reports to external auditors, accompany VXM reports with exported hardware .cfg diff logs to substantiate third-party module parameter equivalence.

Engineer FAQ

Why does VXM show an entire R. STAHL remote I/O rack as removed and re-added?

The station DP address, master system ID, or slave GSD name differs between the two projects. If the parent bus node identifier changes, all subordinate sub-modules are evaluated as new insertions.

Can I ignore hardware differences in VXM and compare only CFC/SFC software?

Yes. In VXM comparison options, you can deselect the 'Hardware Configuration' checkbox and execute comparisons solely across CFC charts, SFC charts, block types, and shared declarations.

Where does STEP 7 store installed GSD files on the engineering workstation?

GSD files for PROFIBUS are stored in <Step7-Install-Dir>\S7DATA\GSD\, and GSDML files for PROFINET are stored in <Step7-Install-Dir>\S7DATA\GSD\GSDML\.