Resolving WinCC Flexible Area Pointer Date-Time PLC Compile Error

Problem Details

The WinCC Flexible Engineering System (ES) returns the compile-time diagnostic Invalid symbol assignment for area pointer 'Date-time PLC' when the HMI project is rebuilt. The error blocks the final compilation pass and prevents the runtime project from being transferred to the operator panel. The message references the area pointer that synchronizes the PLC clock with the HMI clock and points at the symbolic tag that should reference the source data block word (for example, DB 16 DBW 0).

The defect is encountered most often in the following workflow:

1. A STEP 7 project containing an S7-300/S7-400 station is opened, and a WinCC Flexible project is integrated into the STEP 7 project via Insert > Station > SIMATIC HMI Station.
2. The Connections editor of WinCC Flexible binds the HMI tag list to the S7 station.
3. The Area Pointers editor assigns the Date/Time PLC pointer to a symbolic tag that was originally imported from the STEP 7 symbol table.
4. The STEP 7 project is closed (or moved, archived, or compiled with a different STEP 7 version), and the WinCC Flexible project is reopened standalone or from a different work directory.
5. Project > Compiler > All fails with the symbol-assignment error described above.

The visible symptom is identical for offline and online compilation attempts and is independent of the panel type (KTP, TP, MP, or Mobile Panel running WinCC Flexible 2008 SP5 / WinCC Flexible 2008 SP3 / WinCC flexible 2007).

Root Cause Analysis

WinCC Flexible stores area-pointer assignments in two layers:

• Symbolic layer: The tag name as it exists in the connected STEP 7 symbol table (for example, "Date_Time_PLC").
• Absolute layer: The fully-qualified PLC address (for example, DB 16 DBW 0, MW 100, or a bit in a process image).

When the area pointer is configured symbolically and the linked STEP 7 project is not loaded, archived, or the path has been changed, the compiler can no longer resolve the symbolic reference. The fallback to the absolute address fails because WinCC Flexible writes the symbolic name into the configuration while keeping the absolute address only as an unresolved placeholder. The integrity check then raises the error during the Compile pass for the runtime generator. The same root cause applies to all WinCC Flexible area pointers that reference PLC memory: Date/Time PLC, Date/Time HMI (read back), Coordination, Project ID, PLC ID, Screen Number, Job Mailbox, and Acknowledgement.

Three failure modes are observed in the field:

1. Symbol table drift: The symbol was renamed, deleted, or had its address changed in STEP 7 after the WinCC Flexible tag was created. WinCC Flexible continues to display the old absolute address but cannot validate the symbolic name.
2. STEP 7 not open: The WinCC Flexible project is opened on a workstation where the STEP 7 project file (*.s7p) is not accessible at the original path. WinCC Flexible loads the cached project but cannot resolve symbolic tags because the Reconnect step has not been executed.
3. WinCC flexible / STEP 7 version mismatch: The project was edited on one STEP 7 version (for example, STEP 7 V5.5 + SP4) and recompiled on a workstation where only STEP 7 V5.4 or a different service pack is installed. The block container format is incompatible with the symbol table format that WinCC Flexible caches.

Affected Versions and Products

Solution A — Remove the Symbolic Tag and Use Absolute Addressing

The fastest field-proven workaround is to drop the symbolic reference for the area pointer and keep only the absolute address. This is the recommended path when the STEP 7 symbol cannot be reconnected reliably, for example on archived or read-only project directories.

1. Open the WinCC Flexible project in the Engineering System.
2. From the project tree, open Communication > Connections and confirm that the connection to the S7 station still exists. If it is marked (invalid), first repair it via Reconnect as described in Solution B.
3. Open Communication > Area Pointers.
4. Select the row Date/Time PLC.
5. Click the Symbol column of the entry and press Delete to clear the symbolic name. Press Enter to commit.
6. Re-enter the absolute PLC address manually in the Address column. The standard layout uses DB <n> DBW 0 in a clock data block of at least eight words (see Specifications below).
7. Press Enter and confirm the dialog by clicking OK.
8. Save the project and run Project > Compiler > All (Generate Runtime Files).

Verification: the compile log must no longer contain the string Invalid symbol assignment for area pointer. The transfer utility (Project > Transfer > Transfer) must report Transfer completed successfully when the runtime files are pushed to the panel.

Solution B — Re-establish the STEP 7 Link and Reconnect Symbols

If the symbolic reference is required for documentation or for distributed engineering, restore the STEP 7 link instead of removing the symbol. This is the correct long-term fix when the HMI project is integrated into the STEP 7 project.

1. Close WinCC Flexible.
2. Open the STEP 7 project that owns the HMI station.
3. Verify that the data block referenced by the area pointer exists, has the correct length (minimum 8 bytes for the date/time area pointer), and that the symbolic name is present in the symbol table (S7 Program > Symbols). If the symbol was renamed, update the HMI tag accordingly.
4. Re-open the WinCC Flexible project. The synchronization assistant starts automatically because the integrated project detects a more recent STEP 7 timestamp.
5. If the wizard does not start, open Tools > Reconnect (or Options > WinCC flexible > Reconnect). The dialog lists all symbolic tags that cannot be resolved.
6. For the Date/Time PLC row, select the correct symbolic tag from the dropdown and confirm with Apply.
7. Save the WinCC Flexible project.
8. Rebuild the project via Project > Compiler > All.

Solution C — Rebuild the Project from a Clean Cache

If Solutions A and B do not eliminate the error, the cached WinCC Flexible project file is corrupt. Force a regeneration of the symbol cache.

1. Close WinCC Flexible.
2. Browse to the WinCC Flexible project folder (*.hmi or *.log container). Inside the project, navigate to im → <panel name>.
3. Delete the files *.log, *.lsl, and *.bin associated with the panel runtime. Do not delete *.hmi, *.ldf, or the Connections folder.
4. Open the STEP 7 project (integrated scenario).
5. Open the WinCC Flexible project. WinCC Flexible regenerates the runtime files from scratch.
6. Compile via Project > Compiler > All.

If the compile still fails, export the WinCC Flexible project to a fresh directory via Project > Save As and recompile there. This eliminates permission issues on the original share.

Specifications — Date/Time PLC Area Pointer

The Date/Time PLC area pointer transfers the time-of-day from the PLC to the HMI. The PLC writes eight consecutive bytes starting at the configured word address in the format consumed by SET_TIME / READ_CLK on S7-300/400 and WR_SYS_T / RD_SYS_T on S7-1200/1500.

The configured address must point to the first word of the eight-byte clock area. Typical conventions:

• DB 16 DBW 0 — data block 16, word 0, length 8 bytes (recommended for new projects).
• MW 100 — bit-memory area, used when no DB is reserved for time keeping.
• DB 1 DBW 0 — legacy example from the WinCC Flexible samples.

The clock data is written by the PLC using the standard system function SFC 0 (SET_CLK) or by the HMI operator via System > Set Time of Day. When the panel receives a new value from the operator, the Date/Time PLC area pointer is written by the panel to inform the PLC of the change. The pointer is bidirectional and must therefore be located in a writable area on the PLC.

Verification Procedure

1. Compile cleanly: After the fix, Project > Compiler > All must finish with 0 errors, 0 warnings in the output window. Warnings about unused tags are tolerable but must not include Invalid symbol.
2. Runtime transfer: Use Project > Transfer > Transfer or Project > Transfer > Backup/Restore to push the project to the panel. The transfer must end with status Transfer successfully completed.
3. Online clock test: On the panel, open System > Date/Time and change the time. Confirm that the PLC receives the new value by reading the configured data block in STEP 7 online (Monitor/Modify) or by triggering a tag in the PLC program that reads SFC 1 (READ_CLK).
4. Cross-check the pointer direction: If the PLC pushes time to the HMI automatically (for example via SFC 0 on power-up), verify that the displayed time on the panel updates within one second.

Related Area-Pointer Errors

Best Practices for Area-Pointer Configuration

• Reserve a dedicated clock data block (commonly DB 16) with a clear name such as DB_Clock. Document the eight-byte layout in the block header.
• Configure the area pointer with an absolute address and a symbolic reference in parallel, so that the panel can still find the area after a STEP 7 symbol rename.
• Always keep the STEP 7 project open while editing the WinCC Flexible project. WinCC Flexible refreshes the symbol cache in real time only when the STEP 7 project is loaded.
• After every STEP 7 symbol change, run Tools > Reconnect and review the list of unresolved tags before recompiling.
• Maintain a one-to-one mapping between STEP 7 service packs and WinCC Flexible service packs in the engineering image. Mismatches generate silent cache invalidations that surface only at compile time.
• Archive the project as *.zip via Project > Archive before moving it between workstations. Archive files contain both the STEP 7 container and the WinCC Flexible container in a single, byte-stable format.
• For new projects, prefer the TIA Portal with WinCC Professional / Comfort — the area-pointer editor is integrated into the device configuration and uses a single project database that avoids the dual-store (STEP 7 + WinCC Flexible) synchronization entirely.

Migration Path to TIA Portal

WinCC Flexible projects are migrated into the TIA Portal through Project > Migrate project. During migration, every area pointer is re-imported as an HMI tag of the category Area pointer. The migration report lists symbolic tags that cannot be resolved; they must be reconnected manually in the TIA Portal device view. For the Date/Time PLC pointer, the tag name is preserved and the absolute address is updated to the symbolic name automatically when the S7 program is included in the migration scope.