STEP 7 HW Config Shows Missing Modules in Old S7-300 Profibus Projects

Affected environment: SIMATIC STEP 7 V5.4 / V5.5 (incl. SP2 / SP3 / SP4 / SP5) on S7-300 stations with ET 200M (IM 153‑1) Profibus slaves. Project originally commissioned with SIMATIC PDM. Module type observed as missing: 6ES7 321-1BL00-0AA0 (SM 321, 32 DI, 24 V DC).

This reference documents a recurrent fault where a fully editable legacy S7-300 project is suddenly opened in read-only mode, HW Config reports "No changes can be made to this station", and one or more Profibus DP slaves display placeholder slots instead of their configured I/O modules. The fault has been observed to reproduce across multiple PCs, multiple STEP 7 versions, and after every available HW Update.

1. Problem Description

The reported behavior occurs in projects originally created in an early STEP 7 release and reopened years later in a current V5.5 engineering station. The operator receives the message "No changes can be made to this station" immediately on opening HW Config, blocking any insertion, deletion, or parameter modification. ET 200M stations (IM 153‑1) under the Profibus master display empty slots where SM 321 digital input modules are physically configured. The error persists even after:

• Installing every available HW Update (HSP – Hardware Support Package) on the engineering PC.
• Opening the project on a different PC with STEP 7 V5.4.
• Applying STEP 7 V5.5 + SP2.
• Confirming that the affected module MLFB (e.g. 6ES7 321-1BL00-0AA0) is still present in the HW catalog and can be inserted into a fresh station.

The placeholder rendering is non-destructive: the configuration data still resides inside the project database and the PLC, it is simply not drawn or evaluated by the editor in the current session.

2. Affected Modules, Firmware and Versions

See the official STEP 7 V5.5 What's New and HSP list and the SM 321 module manual on the S7-300 Module Data reference page for the canonical MLFB mapping. The IM 153‑1 manual is available under the ET 200M entry.

3. Observed Symptoms

1. HW Config opens. The status bar or the dialog "Edit – Open HW Config" returns "No changes can be made to this station".
2. One or more IM 153‑1 stations show empty slot graphics with a placeholder icon (a hatched frame) where the SM 321 should be located.
3. Clicking once on the Profibus node re-renders the slot list, the SM 321 becomes visible with its order number and parameters.
4. Clicking on any other station, the same station, or a slot of a different module type erases the rendering again. The slot returns to the placeholder state.
5. The placeholder state is independent of the I&M data, the slot address, and the diagnostic buffer of the connected CPU.
6. "Save as with reorganization" (German Speichern unter mit Reorganisation) does not heal the rendering, but it does not lose configuration data either.

4. Root Cause Analysis

Three independent root causes have been reproduced in the field; the visible symptom is identical in all of them.

4.1 Missing or Incomplete HW Update (HSP)

STEP 7 HW Config relies on HSP files (Hardware Support Packages) to extend the module catalog beyond the originally released set. The module 6ES7 321-1BL00-0AA0 was added in HSPs that predate the V5.4/V5.5 distribution media. If the engineering PC received STEP 7 from a volume license or image that pre-dates a particular HSP roll-up, the catalog entry is read but the parameter block for the legacy MLFB may be incomplete. The editor consequently cannot bind the slot to the catalog object and falls back to the placeholder graphic.

4.2 SIMATIC PDM Integration is not Installed

Projects configured with SIMATIC PDM (see SIMATIC PDM manual collection) embed object references that the standard STEP 7 HW Config cannot resolve when PDM is absent. The fault is silent — no warning dialog appears — and the slots bound to PDM-managed objects are blanked out. Reinstalling SIMATIC PDM on the engineering PC and merging its DLLs into the STEP 7 install typically restores the rendering and editing rights.

4.3 Station is Locked because PDM Object is Missing

If the PDM device description (EDD) referenced by the station is no longer present on the PG, STEP 7 protects the station from accidental structural edits. The message "No changes can be made to this station" is a direct consequence: the integrity of the PDM-managed objects cannot be guaranteed. This is the most common root cause for the read-only flag in legacy S7-300 Profibus projects.

5. Diagnostic Procedure

Run the following checks on the engineering PC before modifying the project.

1. Verify the STEP 7 install: Start → SIMATIC → Information → Installed Software. Confirm the version string and the SP level. Record the build number (e.g. K5.5.5.0).
2. Verify all HSPs: Start → SIMATIC → STEP 7 → Install HW Updates. Note the HSP list and the latest installed HSP build (typically visible as a year-quarter stamp, e.g. HSP 0262 2019).
3. Verify PDM: Start → SIMATIC → PDM → Information. PDM must be at the same major version baseline as STEP 7 (PDM V8.x for STEP 7 V5.5, PDM V6.x for V5.4). Mixed baselines corrupt the object manager.
4. Open the project, start HW Config, watch the message bar. Capture the exact text. If "No changes can be made to this station" appears, the station is locked.
5. Click on the affected Profibus node. Verify that the SM 321 becomes visible. If it does, the configuration data is intact; the rendering pipeline alone is failing.
6. Open the project with the archive tool (SIMATIC Manager → File → Archive) and inspect the om003.tx? or om_*.pd? files (object manager) using the S7 Object Viewer if available. Missing object IDs are a strong indicator of root cause 4.3.

6. Solution

Apply the remedies in the order listed. Re-test after each step.

6.1 Reinstall the Missing HSP

1. Download the latest HSP bundle from the Siemens HSP download portal (account required).
2. Close SIMATIC Manager and any S7 online application.
3. Run Start → SIMATIC → STEP 7 → Install HW Updates and select the downloaded HSPs.
4. Reboot the PC; STEP 7 rebuilds the local module catalog at first launch.
5. Open the project, open HW Config, verify the SM 321 is no longer a placeholder.

6.2 Install SIMATIC PDM

1. Obtain the SIMATIC PDM installation media matching the STEP 7 version. For STEP 7 V5.5 SPx, use PDM V8.2 or V9.x as recommended by the PDM/STEP 7 compatibility list (see the SIMATIC PDM compatibility matrix).
2. Run the PDM setup. Accept the integration into STEP 7 when prompted.
3. Apply the matching PDM Service Packs.
4. Re-open the project. HW Config should now allow edits and the placeholders must be replaced by the actual module graphics.

6.3 Re-register the PDM Device Library

If PDM is installed but the station remains read-only:

1. Open SIMATIC Manager → Options → SIMATIC PDM → Device Library.
2. Confirm the device category of the IM 153‑1 and of every HART/PA device that was originally part of the project. The library must contain a green check next to each device.
3. If a device shows red, locate the corresponding EDD on the SIMATIC PDM EDD download center and import it.
4. Reopen the project. The station should now be editable.

6.4 Save As With Reorganization

When the rendering is intermittent and editing is blocked, perform a project reorganization that rewrites the object manager indices:

1. Open the project in SIMATIC Manager.
2. Select the S7 program (or the station) → File → Save As.
3. Enable the option "With reorganization" (German "mit Reorganisation").
4. Choose a new project name; do not overwrite the original until the result is verified.
5. After completion, open HW Config and re-check the affected nodes. In most cases the placeholders are replaced by the proper module graphics.

6.5 Edit the SDB Indirectly as a Last Resort

If the project is still locked and the missing module is critical (e.g. a counter FM with non-documented parameters), edit the System Data Block (SDB) outside of HW Config:

1. Export the SDB container to a file via PLC → Upload Station to PG using a working online connection.
2. Decompile the SDB with a third-party tool (e.g. S7-IBD, S7-Project-Viewer) and verify the slot configuration. Use this step for diagnostics only; do not write back unverified changes.
3. If a complete SDB reconstruction is required, commission a new station with the same topology, then merge the FM parameters from the original project documentation.

7. Commissioning Workflow for a Recovered Station

Once HW Config edits are restored, re-commission the station with the following sequence.

1. Open HW Config, double-click the IM 153‑1, verify the Profibus address matches the rotary switch on the physical module.
2. Verify the slot list: slot 4 must contain the head module, slots 4 through 11 carry the configured I/O. Mismatch in slot number is the most common downstream symptom of a previous placeholder editing attempt.
3. Compile and download HW Config. Watch for SDB download errors in the diagnostic buffer; a "Slot not configured" error means the placeholder was saved to the target CPU and must be cleared by re-downloading the SDB.
4. Use PLC → Compare Online / Offline to confirm the online configuration matches the offline project.
5. Run the standard PROFIBUS diagnostics: Online → Accessible Nodes. All configured slaves must appear with their expected diagnostic LED pattern (green bus, green SF off).

8. Verification Matrix

9. Preventive Measures for Future Projects

• Standardize the engineering PC image. Bundle STEP 7 V5.5 + latest SP, the full HSP set, and SIMATIC PDM V8.x / V9.x in a single deployment image. Document the build numbers in the project header.
• Archive projects with SIMATIC Manager. Always export projects as .s7p archives (not just copied folders). The archive contains all referenced GSD and EDD indices.
• Store GSD/EDD in the project. Use Options → Install GSD File for every Profibus device used, even standard Siemens devices, and re-archive the project after any GSD update.
• Avoid mixing PDM versions. PDM V6 and V8 cannot read each other's project objects. Maintain one PDM baseline per fleet of engineering PCs.
• Document the HSP baseline in the project. Add a comment to the station's object properties (header, "Installation" tab) listing the HSP and PDM versions used during commissioning. Future migrations can then be performed in a controlled manner.
• Use the STEP 7 Version Checker (see the STEP 7 Version Checker tool entry) before opening a project on a new PC.

10. Known Field Issues and Edge Cases

• Editable after second click, blank after third click: The rendering cache is destroyed by redraw events. The configuration is intact; this is purely a UI symptom. PDM reinstallation resolves it.
• Different PCs, same symptom: Rules out a local PC corruption. The project itself carries a PDM reference that no engineering PC can resolve. Reinstall PDM on at least one of the test PCs to confirm.
• Standard SM 321 (not HART, not FM) flagged as missing: Indicates the IM 153‑1 station is bound to a PDM device container. The container loses its sub-objects when PDM is absent. Install PDM and re-archive.
• HSP installed but module still missing: The HSP adds catalog entries for insertion, but the binding of an existing slot requires the original PDM object. HSP alone cannot restore editing of an existing station bound to PDM.
• Function modules (FM 350 / 351 / 352, Siwarex): The EDD is mandatory. Without it, the module is rendered as a generic placeholder and the configuration parameters are inaccessible. See the ET 200M and Siwarex manuals for the device-specific EDD packages.
• Profibus PA devices via PDM: PA masters that delegate device management to PDM show the same placeholder symptom on a missing EDD. See the SIMATIC PDM PA device integration page.

11. Related Configuration Tasks

While the project is open and editable, address the following in the same maintenance window:

1. Update the CPU firmware to the latest available release (download via Siemens firmware update portal).
2. Compare the IM 153‑1 firmware against the released list. The IM 153‑1 (6ES7 153-1AA03-0XB0) firmware 5.x or higher is recommended for projects with HART devices.
3. Re-export the SDB after every configuration change. Store the SDB in the project archive, not in a network share.
4. Update the SIMATIC PDM device library before editing HART or PA parameters.

12. Frequently Asked Questions