Fixing Invalid Message Frame on CU240S PN with IM151-8 CPU

Fixing the "Invalid Message Frame" Error on SINAMICS G120 CU240S PN with ET 200S IM151-8 PN/DP CPU

This technical reference documents the resolution of a recurring STEP 7 V5.5 HW Config symptom in which a SINAMICS G120 Control Unit CU240S PN drops into the device slot of an ET 200S IM151-8 PN/DP CPU as a PROFINET IO Device, but the slot dialog refuses to accept any of the standard telegrams (Standard Telegram 1, 2, 3, 4, 20, 220, 352, etc.). The slot properties report an "invalid message frame" and the PZD length cannot be selected. The same G120 inserted as a PROFIBUS DP device (CU240S DP, CU240S PN with DP fallback profile) loads its telegrams correctly, which is the diagnostic signature pointing to a STEP 7 PROFINET Integration / GSD problem rather than a drive firmware problem.

1. Problem Details

When a SINAMICS G120 with a CU240S PN Control Unit is dragged from the PROFINET IO catalog into the PROFINET IO system of an ET 200S station headed by an IM151-8 PN/DP CPU, the device is created and the IP / device name can be assigned without error. However, opening the slot properties of the G120 (double-click on the drive object, then the configuration tab) produces a dialog that is grayed-out for message frame / Telegramm-Auswahl, with the controller property reporting the string "invalid message frame" or, in the German UI, "ungültiger Telegrammaufbau".

Consequences in the engineering workstation:

• Standard Telegrams 1, 2, 3, 4 (setpoint / actual value) cannot be selected.
• Free telegram configuration (999) cannot be enabled.
• The PZD count (number of words in each direction) cannot be modified, so the cyclic I/O mapping in the user program is impossible to derive.
• Compilation (Station → Save and Compile) emits no error, but the generated SDB will not contain the expected PZD I/O addresses, leading to a download-time rejection on the IM151-8 ("Configuration error", SF LED on G120, BF LED flashing on the CU240S PN).

The same G120, inserted on a PROFIBUS DP segment (CU240S DP, or G120 with GSD SIEM811F.GSD / SI01811F.GSD), shows the full family of message frames (Standard Telegram 1, 2, 3, 4, 20, 220, 352, Siemens Telegram 110, 111, 370, 371) and is selectable. This contrast is the single most useful diagnostic: the G120 firmware, the drive parameters p0922 / p2079, and the bus cable are exonerated; the failure is inside the STEP 7 PROFINET Integration layer.

2. Affected Hardware and Software Versions

The following components and software versions have been observed to produce or to be affected by the symptom. Versions outside these ranges should be checked against the relevant Siemens compatibility tables.

3. Root Cause Analysis

Three independent causes have been observed in the field, all of which collapse to the same STEP 7 dialog behavior. A correct first-time fix is to address all three in sequence; the order below is the order in which they should be ruled out.

3.1 Outdated STEP 7 V5.5 PROFINET GSDML parser

STEP 7 V5.5 ships with a built-in PROFINET device-description parser. Earlier service packs of V5.5 cannot decode the module/submodule structure of the SINAMICS G120 GSDML revisions ≥ V2.1 (the G120C, G120 with CU240S PN, and G120P families). The parser silently produces an empty submodule list, which STEP 7 then reports as "invalid message frame". The fix is distributed as Hotfix 4 for STEP 7 V5.5, which is part of the cumulative HF collection; later service packs (V5.5 SP4 and onward) already include the equivalent corrections.

3.2 Drive ES / SIMOTION Scout install-order conflict

DriveES and SIMOTION Scout both install GSD / GSDML catalogs into the shared SIMATIC device-description store (typically under ...\Siemens\Automation\Device Descriptions\). When DriveES is installed after SIMOTION Scout, parts of the G120 GSDML tree that Scout installed can be overwritten or merged inconsistently, and the IM151-8 PROFINET IO controller catalog that Scout shipped with may shadow the DriveES update. The resulting catalog entry looks superficially correct (icon present, slot visible) but the underlying module record is broken, and the slot dialog falls back to the "invalid message frame" state. The remedy is to uninstall both, then install Scout first and DriveES second, in the order Siemens documents for the SIMOTION / DriveES coexistence.

3.3 Damaged telegram definitions (GSD/GSDML file corruption)

On workstations where DriveES was installed, uninstalled, and reinstalled — or where the GSDML was edited manually — the local copy of the SINAMICS G120 GSDML in the STEP 7 catalog can become truncated or mismatched against the XMLDeviceDescriptionCache index. The GSDML file in the file system is intact, but STEP 7's cached index considers it invalid. The slot dialog will again surface the same "invalid message frame" string. The remedy is a GSD repair, described in Section 7 below.

4. Preconditions for Correct Telegram Selection

Before any software repair, verify the engineering station meets the minimum preconditions. A defect anywhere in this list will reproduce the symptom regardless of HF4, install order, or GSD repair.

1. Administrator rights on the engineering PC. STEP 7 V5.5 HW Config writes to HKLM\SOFTWARE\Siemens\Automation and to the protected GSDML cache; non-admin sessions will appear to install without error but silently fail to update the catalog.
2. Matching GSDML / GSD major version. The GSDML shipped in the DriveES / G120 GSDML package must be at the same or higher major version as the CU240S PN firmware in the drive. For CU240S PN firmware V4.5 / V4.6 / V4.7 the GSDML revision is V2.32 or higher; for firmware V5.x the GSDML is V2.35 or higher. Mismatches manifest as "invalid message frame" or as a slot list that is empty.
3. Catalog rebuild cache. After any GSDML update, the catalog index in ...\Siemens\Automation\Catalog must be rebuilt (Options → Install HW Updates → … → Rebuild catalog) before the new devices appear correctly. Skipping this is the single most common cause of a half-working catalog.
4. Project saved and closed. HW Config reads catalog entries only at object-plug time and at compile. The project must be saved and closed, then re-opened, after any catalog or HF update. A working catalog against an open project continues to use the cached in-project schema.
5. No active PG/PC interface conflict. The PROFINET IO controller (IM151-8) and the PG must be on the same subnet for the G120 to be reachable at download; this is a separate test but is often confused with the slot-dialog problem. Use the menu PLC → Ethernet → Edit Ethernet Node to confirm reachability before chasing catalog errors.

5. Solution 1 — Apply STEP 7 V5.5 Hotfix 4 (HF4)

This is the primary fix. Apply HF4 (or any later cumulative hotfix) on the engineering station, then re-open the project.

5.1 Procedure

1. Close all SIMATIC applications (SIMATIC Manager, HW Config, NetPro, Scout, DriveES, STARTER).
2. Verify the current STEP 7 build: open SIMATIC Manager → Help → About → Installed Software and switch the display to Installed Software (or the "Products List" / "Components List" tabs that the original symptom report references). Note the exact build number of STEP 7 V5.5.
3. Locate Hotfix 4 for STEP 7 V5.5 in Siemens Online Support (search entry ID 67549496 / 57005835 family, or the cumulative HF collection that includes HF4 — these IDs are part of the standard STEP 7 V5.5 patch set).
4. Download STEP7_V55_HF4.exe (or the cumulative package) and any prerequisites it lists (typically a recent SIMATIC device-description base hotfix).
5. Run the hotfix as Administrator. The installer detects existing STEP 7 V5.5 and patches the binary tree; do not uninstall STEP 7 first.
6. Reboot. Confirm the new build number in Help → About; it should change from V5.5 + SPx to V5.5 + SPx + HF4 (or higher).
7. Re-open the project, open HW Config, navigate to the G120 slot, and verify the message-frame list is now populated.

5.2 What HF4 actually changes

HF4 is a cumulative patch set; among other items it updates:

• The PROFINET GSDML parser in HW Config to correctly enumerate the G120 submodules.
• The NetPro PROFINET IO controller index used by the IM151-8 PN/DP CPU build.
• The Device Description Cache (DDC) and the catalog rebuild routine used by Options → Install HW Updates.

After HF4, the dialog at the G120 slot shows the Standard Telegram drop-down populated with the PROFIdrive profile telegrams 1, 2, 3, 4, 20, 220, 352, and the Siemens manufacturer-specific telegrams 110, 111, 370, 371, plus the Free Telegram Configuration (999) option for custom PZD layouts. Selecting a telegram enables the PZD count (e.g. 2/2 for Telegram 1, 6/6 for Telegram 3, 4/4 for Telegram 4, 2/6 for Telegram 20) and the I-address / Q-address fields become editable.

6. Solution 2 — Correct DriveES / SIMOTION Scout Installation Order

If HF4 alone does not clear the symptom, or if the original symptom persists immediately after a fresh DriveES install, the install order is the next thing to address.

6.1 Procedure

1. Open Control Panel → Programs and Features on the engineering PC. Confirm the install order of SIMOTION Scout V4.2 and DriveES V5.5 by the Installed On date column.
2. If DriveES is listed after Scout, DriveES is likely overwriting or shadowing the G120 GSDML in the shared catalog. Uninstall DriveES.
3. Open the catalog directory directly: %ProgramFiles%\Siemens\Automation\Device Descriptions (or ...\Siemens\Automation\PNIO\GSD on some installations). Look for two copies of the SINAMICS G120 GSDML: GSDML-Vx.x-Siemens-Sinamics_G120_CU240S_PN-yyyymmdd.xml. If both exist, the older one (lower version) is the one Scout installed; the newer one is the DriveES version. After the uninstall the DriveES copy should be removed.
4. Verify Scout is still installed. Repair or re-install Scout if necessary.
5. Reinstall DriveES V5.5 as Administrator. Watch the installer dialog for any "merged catalog" warnings and accept the default merge behavior unless the Siemens readme specifies otherwise.
6. Rebuild the STEP 7 catalog: Options → Install HW Updates → … → Rebuild catalog.
7. Re-open the project. Test the G120 slot.

6.2 Why this works

DriveES installs the G120 GSDML into the shared Device Descriptions tree; if a previous version (from Scout) is present, DriveES can either update the entry, append, or silently skip the write if the file is read-only. When the update is skipped, STEP 7 continues to use the older Scout GSDML that does not know about the latest CU240S PN firmware submodules — exactly the surface symptom observed. Reinstalling in the correct order (Scout first, then DriveES) lets the DriveES writer win the catalog.

7. Solution 3 — Repair Damaged Telegram Definitions (GSD / GSDML Cache Repair)

If the symptom persists after HF4 and the install-order fix, the catalog index is likely damaged. STEP 7 reads the GSD/GSDML file from disk but indexes it in a separate XMLDeviceDescriptionCache and Catalog binary. A damaged index must be rebuilt.

7.1 Procedure

1. Close all SIMATIC applications.
2. Delete (or rename) the catalog index: %ProgramFiles%\Siemens\Automation\Catalog\Catalog.bak and Catalog.dat if present. Delete the GSDML cache: %ProgramFiles%\Siemens\Automation\Device Descriptions\XMLDeviceDescriptionCache. Do not delete the GSDML XML files themselves.
3. Verify the SINAMICS G120 GSDML is still present in ...\Siemens\Automation\Device Descriptions\PNIO. If absent, re-install the GSDML from the latest DriveES / G120 GSDML package on Siemens Online Support.
4. Re-launch SIMATIC Manager. STEP 7 will rebuild the index on first HW Config open.
5. Open HW Config; the G120 will re-appear in the PROFINET IO catalog at the correct position. Insert it; the slot dialog should now present the message-frame list.

7.2 Verification of the GSDML source

Open the GSDML file in a text editor and confirm the <ModuleList> contains the G120 submodules. Search for the strings "Standard Telegram 1", "Standard Telegram 3", "Free Telegram Configuration (999)" in the <ModuleItem> entries. If they are missing the GSDML itself is wrong; replace with a fresh copy from Siemens Online Support.

7.3 GSD file re-install via the STEP 7 GUI

As an alternative to manual repair, use Options → Install HW Updates → … → Install GSD file. Browse to the GSDML XML and let the wizard perform the install + catalog rebuild in one operation. This is the recommended first attempt when the user is uncomfortable deleting cache files manually.

8. Verification Procedure in HW Config

After each of the above three solutions, perform the following verification sequence. The verification either passes (slot dialog populates with valid telegrams) or fails (the symptom persists and the next solution is required).

1. Open the project, open HW Config.
2. Click the G120 device object under the IM151-8 PROFINET IO system.
3. Open Properties → Configuration tab.
4. Confirm the Message Frame drop-down is populated and selectable.
5. Select Standard Telegram 1 (2 PKW, 2 PZD — minimum default). Click OK.
6. Confirm the I-address and Q-address fields in the slot details are now editable and show the expected offsets (typically the IM151-8 reserves the I/O range I 0..7 for the SINAMICS PKW and I 8..11 for the PZD by default, but the exact range depends on the ET 200S module order).
7. Compile the station (Station → Save and Compile). The download-ready SDB should be created without "Configuration error" warnings.
8. Download the configuration to the IM151-8 (PLC → Download). The IM151-8 should report RUN without SF / BF errors. The G120 should report ready-to-operate (the G120 RDY LED green) within a few seconds of the cyclic data being established.

8.1 Verification matrix

9. Cross-Reference: Why DP Works and PN Fails

The diagnostic contrast "DP works, PN fails" deserves a closer look, because it is what points unambiguously to the STEP 7 catalog rather than the drive.

PROFIBUS DP GSD files are flat ASCII files with a well-defined structure that has not changed materially in 15 years. The STEP 7 GSD parser for DP is therefore extremely stable across service packs; the G120 GSD files (e.g. SIEM811F.GSD) parse identically on a vanilla STEP 7 V5.5 and on V5.5 + HF4. The PROFINET GSDML parser, by contrast, handles nested XML schemas with versioning, and the G120 GSDML schema has had several major revisions (V2.0, V2.1, V2.25, V2.31, V2.32, V2.35). An old STEP 7 build will refuse to load a newer GSDML, and a damaged STEP 7 install will load the GSDML but fail to enumerate the submodules. Both produce the same dialog text: "invalid message frame".

Practical implication: if the same G120 (same firmware, same drive parameters) appears correctly when inserted on a DP segment in the same project, you can stop checking the drive. The remaining fix space is entirely on the STEP 7 / catalog side.

10. Alternate Path: Migrating to TIA Portal

For greenfield stations, or for stations where the STEP 7 V5.5 environment is already at the end of its support window, the modern path is to migrate to TIA Portal. In TIA Portal the G120 GSDML is delivered as part of the SINAMICS G120 Support Package (or installed by HSP) and the message-frame dialog at the G120 slot is the same kind of slot-properties dialog but is far more tolerant of GSDML major-version mismatches.

For the IM151-8 PN/DP CPU, the migration is more involved: the IM151-8 is an ET 200S CPU and is supported in TIA Portal as a third-party / legacy device via GSD import. Many integrators choose to migrate to a S7-1500 ET 200S station or to a S7-1500 with a PROFINET interface module for the G120, rather than re-host the IM151-8 in TIA. If the application requires keeping the IM151-8, the typical pattern is to leave the IM151-8 in STEP 7 V5.5 and run a mixed environment: the ET 200S station in STEP 7 V5.5 + HF4, and the rest of the plant in TIA Portal, with a PN/PN coupler between them.

11. Field-Commissioning Checklist

Use this checklist at the cabinet to reduce time-to-recovery on a fresh install.

• STEP 7 V5.5 + latest SP + HF4 or later — verified in Help → About.
• DriveES V5.5 installed after SIMOTION Scout (when both are present).
• Latest GSDML package for SINAMICS G120 CU240S PN installed and catalog rebuilt.
• Catalog rebuild performed (Options → Install HW Updates → … → Rebuild).
• Project saved, closed, re-opened after every catalog / HF change.
• PG/PC interface set to the correct PROFINET network adapter (S7ONLINE access point).
• PROFINET device name assigned to the G120 (PLC → Ethernet → Assign PROFINET Device Name) and IP confirmed reachable via Edit Ethernet Node.
• IM151-8 firmware version on a release that supports the loaded GSDML.
• Drive parameter p0922 = the PROFIdrive telegram selected in HW Config.
• Drive parameter p2030 = 2 (PN interface) and p2031 set if a second interface is used.
• CU240S PN switch S1 (PROFINET address / DHCP) set to the expected mode before power-up; S1 changes only take effect after a power cycle.

12. Frequently Asked Questions