STEP 7 V5.4: Recovering Lost Data Block and UDT Comments from an Online PLC

This technical reference documents the field-proven procedure to restore lost comments inside SIMATIC S7-300 and S7-400 Data Blocks and UDTs programmed with STEP 7 V5.4. The procedure exploits the fact that the offline project archive retains human-readable comment text, while the online PLC CPU only contains compressed machine code. By copying the live (comment-stripped) blocks from the online CPU into a comment-bearing backup project, the engineer effectively re-hydrates the live program with the missing documentation.

1. Problem Statement

After one of the following events, the offline STEP 7 V5.4 project suddenly shows empty Block Title, Block Comment, Network Title, Network Comment, and Symbolic Comment fields for one or more DBs or UDTs:

• A new project was created from the File > New Project wizard and blocks were uploaded with PLC > Upload Station to PG.
• The S7 program was dragged from an archive into a freshly created project (program-level move, not block-level move).
• Hardware was reconfigured with HW Config and the project was recompiled.
• The PC hostname was changed, breaking the path references inside the STEP 7 database.
• An older service pack (e.g. V5.4 SP2) opened a project last saved with V5.4 SP5, silently stripping long multi-line comments.
• The Options > Customize > Editor > Comments setting was unintentionally toggled off.

Despite the comments being absent, the program logic in OB1, FB, FC, and DB still compiles and executes. Only the documentation layer is gone. The PLC itself never stored those comments in the first place - it only stores compressed block content in load memory (MMC card or internal flash) and in work memory (RAM).

2. Why Comments Disappear in STEP 7 V5.4

STEP 7 V5.4 stores the user project in two distinct locations, and the comments live only in one of them:

The MC7 code inside the CPU is the binary result of the compiler and contains no comment strings whatsoever. Uploading a station therefore yields blocks with empty comment fields. The original comment text only survives in the offline .s7d file or in STL/SCL source files that were saved to disk using File > Generate Source.

Consequences:

• If the only copy of the project is the CPU (no recent backup, no source files), comments are unrecoverable and must be re-typed.
• If a backup exists, the backup's offline database contains the comments. The CPU contains the current code. The two must be merged.
• If a source file exists, regenerating the blocks from the source restores the comments without touching the CPU.

3. Recovery Strategy Decision Matrix

4. Prerequisites

Before executing any of the recovery procedures, confirm the following:

1. STEP 7 V5.4 (any SP) is installed on the engineering station.
2. You have read rights to the project folder containing the comment-bearing backup.
3. You have physical or routed (e.g. through a CP343-1 Lean) online access to the target CPU with PG/PC interface set to TCP/IP, MPI, or PROFIBUS as appropriate.
4. The PG/PC interface is correctly assigned in Options > Set PG/PC Interface (e.g. TCP/IP -> Intel(R) PRO/1000... for an S7-300 with CP343-1, or PC Adapter (MPI) for the classic MPI cable).
5. No write-protected MMC is currently inserted that would prevent the CPU from accepting a download.
6. You have created a fresh archive of the current (comment-stripped) project before any recovery action.

5. Solution A - Online/Offline Block Merge (Primary Method)

This is the field-proven technique. The principle is:

• Open the comment-bearing backup in SIMATIC Manager. This is the container for comment text.
• Establish an Online view of the same CPU. The online view is the container for the most up-to-date MC7 code.
• Copy the online blocks (excluding SDBs and system blocks) into the offline project's Blocks folder with Overwrite enabled.
• Save the resulting project - it now contains the latest code with all the original comments.

5.1 Procedure

1. Insert the STEP 7 V5.4 installation DVD or mount the ISO. Open SIMATIC Manager from the Windows start menu: Start > SIMATIC > SIMATIC Manager.
2. From the menu, choose File > Retrieve and browse to the comment-bearing backup file. Default extension: *.zip or the original archive folder.
3. Extract the project to a new working directory, e.g. D:\STEP7\Recovery\Project_With_Comments.
4. In the project tree on the left, expand SIMATIC 300 Station (or SIMATIC 400 Station) > CPU > S7 Program > Blocks. Verify that the DBs and UDTs still show their comments by double-clicking one - the Block Title and Block Comment rows at the top of the editor should contain text.
5. Click the Online button in the toolbar (or press Ctrl+Alt+O). The project view switches to the Online window showing the live CPU contents.
6. Navigate to Online > [Your CPU] > S7 Program > Blocks. You will see all blocks currently loaded on the CPU. Comment fields will appear empty - this is expected.
7. Select all user blocks. Use the menu Edit > Select All, then deselect the system blocks (SDBs, SFBs, SFCs, SFB-instances inserted as system) by holding Ctrl and clicking them. The blocks you want are:
   • OB1, OB10, OB35, OB100, OB101, OB102 (organization blocks)
   • FB1 ... FBxxx (function blocks)
   • FC1 ... FCxxx (functions)
   • DB1 ... DBxxx (data blocks)
   • UDT1 ... UDTxxx (user defined types)
   • Any instance DBs (DBxxx associated with an FB)
   Leave SDB entries (System Data Blocks) and SFB/SFC entries untouched - they are tied to hardware configuration and CPU firmware and must not be overwritten from offline.
8. Right-click the selection and choose Copy (or Edit > Copy, or Ctrl+C).
9. Click the Offline button (or Ctrl+Alt+O again) to return to the offline project view.
10. Right-click the Blocks folder of the offline project and choose Paste (or Ctrl+V).
11. A dialog will appear for each block: "Do you want to overwrite the existing block <DBxxx>?". Click Yes to All to accept the overwrite of every user block.
12. Wait for the paste to complete. SIMATIC Manager will show a progress bar in the status line.
13. Save the project: File > Save (or Ctrl+S).
14. Re-archive the project immediately: File > Archive and store the new zip file with a timestamped name.

5.2 Verification After Method A

1. Double-click any DB (e.g. DB100) in the Blocks folder. The Block Title and Block Comment fields at the top of the data view must contain text.
2. Open the Declaration View tab. Each row's Comment column must show the original description (e.g. "Motor speed setpoint in RPM").
3. Open a UDT (e.g. UDT20). The UDT comment should be intact and the individual member comments should be present.
4. Open FB1, navigate to each network, and verify the Network Title and Network Comment rows are filled in.
5. Switch to Online view and compare: the online blocks should now have empty comment fields (because the CPU strips them) but the program logic must match the offline blocks exactly. Use PLC > Compare for a detailed online/offline comparison.

6. Solution B - Selective DB/UDT Copy Between Archives

When the PLC is not reachable but two project archives exist on disk (one with comments, one with the latest code), you can copy DBs and UDTs directly from the older comment-bearing archive into the newer one. The constraint is that the DB/UDT structure must be identical between the two archives, or the paste will be rejected with the error "The block structure differs".

6.1 Procedure

1. Retrieve both archives into separate working folders:
   • D:\STEP7\Archive_Old_WithComments\ - older archive, comments intact
   • D:\STEP7\Archive_New_Current\ - newer archive, comments missing
2. Open SIMATIC Manager with the new archive.
3. Open a second instance of SIMATIC Manager by launching it again from Start > SIMATIC > SIMATIC Manager. Open the old archive in the second instance.
4. In the old-instance window, navigate to the source Blocks folder. Select the DBs and UDTs you want to copy (e.g. DB10, DB11, DB20, UDT1, UDT2).
5. Right-click > Copy, or press Ctrl+C.
6. Switch to the new-instance window, click on its Blocks folder, and Paste (Ctrl+V).
7. Confirm Yes to All when prompted to overwrite.
8. Open a DB to verify that the comment text now appears in the Block Comment and per-row Comment columns.

7. Solution C - Re-compile From STL or SCL Source

If a source file was generated before the comments were lost, it is the most reliable recovery artifact because it is plain text and can be opened in any editor for inspection.

7.1 Locate the Source

1. In SIMATIC Manager, check the Sources folder under S7 Program. Look for files of type STL source or SCL source.
2. If a source file exists with a name such as FB100_SOURCE or ALL_BLOCKS, double-click it to open in the STL or SCL editor.
3. Verify that the source contains the // STL comment markers or the SCL (*...*) and // comment blocks.

7.2 Regenerate the Block

1. From the source editor, choose File > Compile (or press Ctrl+B in the STL source editor).
2. STEP 7 will create a new block in the Blocks folder that matches the source. The block retains every comment from the source.
3. Open the new block to verify the comments appear.
4. Delete the old (comment-stripped) block if the new one has the same number, accepting the overwrite prompt.

8. UDT-Specific Recovery Notes

UDTs (User Defined Types) behave differently from DBs in two important ways:

The original symptom report from the user "Eddie" mentioned that he could not enter the UDT under the Type column of a DB declaration. This happens when the UDT is missing from the target project's Blocks folder. Fix it by first pasting the UDT (from the comment-bearing backup) into the Blocks folder of the target project, then returning to the DB declaration to insert the UDT reference.

8.1 Procedure to Recover a UDT and Re-link It

1. Open the comment-bearing backup in a second SIMATIC Manager instance.
2. Locate the UDT (e.g. UDT5) in Blocks.
3. Copy with Ctrl+C.
4. Paste into the new project Blocks folder.
5. Open the DB that references UDT5. In the Declaration View, the rows that were previously "UDT5" in the Type column will now resolve correctly because the UDT is present.
6. Save the DB and verify that the UDT's row comments appear inline in the data view.

9. Common Pitfalls and Edge Cases

9.1 "The block has a different interface" error during paste

The DB or UDT structure has changed between archives. The paste is blocked to prevent data corruption. Do not force it. Either:

• Use Method A (Online/Offline merge) so the live code is the destination, not the source.
• Manually re-create the missing comments in the new structure.

9.2 Comments disappear again after Save

STEP 7 V5.4 with no service pack installed has a known issue where comments containing non-ASCII characters (e.g. German umlauts, Cyrillic, CJK) are lost on save. Apply the latest service pack from the Siemens Industry Online Support portal.

9.3 Online block size smaller than offline block

The online block in Online > Blocks is always smaller than the offline block in Blocks because comments are stripped. This is normal and not a sign of corruption.

9.4 Project language

If the project was created in German (object language = Deutsch) and the PG has only the English language pack installed, comments may appear empty. Switch the object language via Options > Language for Display Devices and re-open the project.

9.5 PC hostname change

STEP 7 V5.4 stores absolute paths in the s7lg0000.lis index file. If the PC hostname changed, comments may fail to load. Either rename the PC back to the original name or use File > Reorganize to rebuild the index.

10. Process Flow Diagram

11. Prevention and Long-Term Best Practices

1. Archive before every modification. Use File > Archive and keep at least the last 10 archives in a revision-controlled folder structure (e.g. \\fileserver\projects\PlantA\S7-400_Batch3\2024-01-15_1430.zip).
2. Generate STL or SCL source files for every FB, FC, DB, and UDT after each approved revision. Sources are plain text and survive backup media degradation far better than binary .s7d files.
3. Configure the STEP 7 autosave option via Options > Customize > General to back up working files every 15 minutes to a dedicated folder.
4. Use the Symbol Table (S7T) for as much documentation as possible. Symbols are stored separately and are easier to recover than inline block comments.
5. Avoid creating new projects from uploaded stations unless absolutely necessary. Always open the existing offline project and download it instead.
6. Apply the latest STEP 7 V5.4 service pack from the Siemens Industry Online Support portal to address the non-ASCII comment corruption issue.
7. Enable the PG access protection on the CPU to prevent unauthorized stations from accidentally uploading the project without comments.

12. Reference: Where STEP 7 V5.4 Stores Comments

For a deeper understanding of the storage mechanism, the comment strings are stored in these locations within a STEP 7 V5.4 project:

For authoritative documentation, refer to:

• Siemens Industry Online Support - main portal for STEP 7 manuals, firmware, and service packs
• STEP 7 V5.4 Programming and Operating Manual (entry ID 109742403) - covers the online/offline project model
• STEP 7 V5.4 Reference Manual: Software Installation (entry ID 1117397) - covers service pack contents and bug fixes
• SIMATIC S7-300 CPU 31xC and CPU 31x Operating Instructions - hardware-level online behavior
• SIMATIC S7-400 CPU 41x Operating Instructions - hardware-level online behavior

13. Frequently Asked Questions