Resolving PCS7 V5.1 'Nonexistent Tags' Error in WinCC Tag Linking

Problem Summary

Engineers maintaining SIMATIC PCS7 V5.1 plants routinely add new analog or digital signals to the AS program (typically via CFC charts on an S7-400 CPU) and then attempt to bind those new tags to existing WinCC picture objects on the OS. The CFC logic works — the value updates correctly when watched in the CFC online view — but at the moment the engineer clicks OK in the tag-selection dialog, a secondary dialog titled "Creation of Nonexistent Tags" ("Anlegen nicht vorhandener Tags" in German locales) appears. Its left pane lists the desired tag name; its right pane prompts for a destination: Internal Tags or SIMATIC Protocol Suite. Choosing either branch creates a local placeholder in the WinCC tag database that is decoupled from the actual AS-side symbol, which then behaves erratically at runtime — either reading a stale value, an address of zero, or failing the compile on download.

This symptom is not an error in the new CFC code and not a fault in the picture. It is a synchronization gap between the AS-side symbol/image description and the OS-side WinCC tag database that the engineer must close manually in PCS7 V5.1 by running a PLC-OS Transfer (and, where appropriate, an OS Compile). The remainder of this article documents the precise menu paths, the architectural reasons for the behavior, the differences versus PCS7 V7.0+ where the workflow is partially automated, and the verification procedure that confirms the gap is closed.

PCS7 ES / AS / OS Architecture Context

To understand why WinCC demands a manual transfer step in V5.1, the role of each station in the PCS7 plant model must be clear. PCS7 separates engineering, control, and operation across three logical roles that may be co-located on one PC or distributed across many.

The ES is the only station that knows the symbolic name of a tag and the absolute PLC address behind it. The AS knows the address and the live value but not the symbol. The OS needs both — the symbol to display in the picture and the address to poll the AS at runtime. The bridge that carries the symbol-to-address mapping from ES to OS is the PLC-OS Transfer, which writes a generated image description into the OS project's \<OS>\<CPU name>.LDB file (or its V5.1 equivalent). Without that file, the WinCC tag database has no entry for the new CFC variable, and the tag-selection control falls back to its "create local placeholder" behavior, which is the dialog in question.

Root Cause: ES/OS Tag Database Synchronization Gap

When a CFC chart is compiled and downloaded, the AS-side symbol table on the ES is updated. The WinCC tag database, however, is a separate, OS-local data structure (technically a Microsoft Access MDB in early WinCC versions and a SQLite/embedded store in later ones, but architecturally isolated from the AS project). The two structures are not kept in lockstep by the CFC compile step. In PCS7 V5.1, three explicit actions are required to keep them aligned:

1. Compile the CFC/SFC chart (or the S7 program) — updates the ES-side symbol table and generates the S7 downloadable image.
2. PLC-OS Transfer — exports the AS-side symbol information into the OS project's tag database.
3. OS Compile (where picture regeneration is required) — regenerates the OS picture DLLs and any cross-references that the picture depends on.

Skipping step 2 is by far the most common cause of the "Creation of Nonexistent Tags" prompt. In V5.1 the workflow is non-intuitive because steps 1, 2, and 3 are launched from different menus, and step 2 is not flagged as mandatory by the CFC compile dialog. V7.0+ partially mitigates this by bundling steps 2 and 3 behind a single "OS Compile" wizard, but V5.1 engineers must remember to invoke the transfer explicitly.

Solution A: PLC-OS Transfer Procedure in PCS7 V5.1

The PLC-OS Transfer is the canonical fix for the symptom. Execute it after every CFC change that introduces a new tag.

Menu Path (SIMATIC Manager)

Step-by-Step

1. Open the SIMATIC Manager and load the multi-project (or single-project) containing the OS you are editing.
2. Select the OS station in the component view (right pane) — single-click, do not double-click into it.
3. From the menu bar, navigate to Options → PLC-OS → Transfer. In some V5.1 service packs the menu reads Options → AS-OS Transfer; both are equivalent.
4. The PLC-OS Transfer wizard appears. Confirm the Source AS (S7 program) and Target OS (the WinCC project) — both should be pre-filled from the project structure.
5. Click Transfer. A progress bar reports the number of tags created, updated, and deleted on the OS side.
6. Wait for the confirmation dialog ("Transfer successfully completed"). Do not interrupt the transfer while the OS project is open in WinCC Explorer; close WinCC Explorer first if you have it open.

Expected Outcome

After a successful transfer, re-open the WinCC picture in Graphics Designer. The tag-selection dialog will resolve the new symbol directly from the WinCC tag database; the "Creation of Nonexistent Tags" dialog will no longer appear for that variable. Runtime polls from the OS will read the correct address from the AS.

Solution B: OS Compile Procedure

Some picture regeneration scenarios — for example, when a CFC block instance name is renamed or a new SFC chart is added — also require an OS Compile in addition to the PLC-OS Transfer. In V5.1 the compile command is less prominent than in V7.0+, which is why engineers migrating from V5.1 to V7.0 often search in vain for an obvious button.

Locating the OS Compile Command in V5.1

There are three ways to invoke it; use whichever is most accessible in your installation:

1. Right-click context menu: In the SIMATIC Manager component view, right-click the OS object and choose OS Compile from the context menu. This is the most discoverable route in V5.1.
2. Menu bar: With the OS selected, use Options → OS → Compile. Some installations expose this under Edit → Compile OS.
3. OS Station Editor: Double-click the OS to open the station editor, then choose Station → Compile from its menu bar.

OS Compile Parameters to Verify

PCS7 V5.1 vs V7.0+ Workflow Comparison

Engineers who learned PCS7 on V7.0 or later are often surprised by V5.1's separate menus. The table below captures the functional differences that matter for tag synchronization.

The underlying data flow is identical across versions; only the user interface that orchestrates it differs. Engineers porting V5.1 projects to V7.0+ should still understand the two distinct concepts (Transfer and Compile) because the V7.0+ wizard exposes them as separate steps in its detailed log.

Step-by-Step Verification

After running the PLC-OS Transfer (and OS Compile, if applicable), confirm that the synchronization gap is actually closed. A transfer that reports "successful" but silently fails on a malformed symbol still leaves the dialog active.

1. Check the WinCC tag database. Open WinCC Explorer → Tag Management → [your channel, e.g., SIMATIC S7 Protocol Suite → S7-400 station] and confirm the new tag is listed with the correct data type and address. If it is absent, the transfer did not actually pick it up — verify the CFC chart is in the compiled S7 program and re-run the transfer.
2. Re-open the Graphics Designer picture that previously triggered the "Creation of Nonexistent Tags" dialog. Re-bind the tag and confirm the dialog no longer appears.
3. Compile the picture only (Graphics Designer → File → Compile) to surface any object-level issues that the OS-wide compile may have missed.
4. Activate WinCC Runtime in test mode on the ES (or on a stand-alone OS) and observe the picture. The new value should track the CFC online value within one OS acquisition cycle (default 1 s for a polled tag; 500 ms typical for a fast analog).
5. Inspect the OS server's alarm and trend logs for any tag-resolution warnings raised by the runtime during startup. A healthy synchronization produces no warnings related to the new tag.

Configuring TCP/IP-Based PLC-OS Transfer

For distributed plant topologies where the ES and OS are on separate subnets — common in large V5.1 installations — Siemens documented a TCP/IP-based PLC-OS transfer option that avoids the legacy MPI/Industrial Ethernet coupling. The default V5.1 transfer assumes the ES and OS are reachable over the project's configured S7 connection; if not, the transfer silently produces an empty result and the symptom persists.

Enable TCP/IP PLC-OS Transfer

1. In SIMATIC Manager, select the OS object.
2. Choose Options → PLC-OS → Transfer via TCP/IP (the precise label varies by V5.1 service pack; SP4 and later expose this option explicitly).
3. In the dialog, enter the IP address of the target OS server (the WinCC runtime PC). The default port is the S7 protocol port (102/TCP).
4. Confirm the S7 connection name matches an existing NetPro connection; otherwise the transfer will fail with a "connection not found" warning.
5. Run the transfer and observe the diagnostic log. A successful TCP/IP transfer reports the same confirmation message as the local transfer.

Common Related Errors and Diagnostic Matrix

Engineers sometimes misdiagnose the "Creation of Nonexistent Tags" dialog as a different fault. The table below maps the most frequent V5.1 symptoms to their real root causes and the appropriate remedy.

Best Practices for ES/OS Synchronization

Adopt the following discipline in PCS7 V5.1 projects to prevent recurrence of the "Creation of Nonexistent Tags" symptom and to keep the AS and OS projects maintainable across engineer handovers.

1. CFC compile → PLC-OS Transfer → AS download → OS Compile → runtime test — execute these five steps in that order for every AS-side change. Document them on a project checklist posted at the ES.
2. Close WinCC Explorer on the OS server before running the PLC-OS Transfer. A live WinCC Explorer holds file locks on the tag MDB and aborts the transfer with a write-protected warning.
3. Avoid manually creating tags in WinCC Explorer for variables that exist on the AS. Every AS-side variable should propagate through the transfer pipeline; manual tags become orphan entries that complicate the next transfer.
4. Use S7_m/c attributes on CFC chart I/O to control which symbols are exported to the OS. Symbols marked with the appropriate attribute are included in the transfer; unmarked ones are filtered out, which is sometimes the cause of "missing" tags even after a successful transfer.
5. Tag naming convention. Keep a project-wide naming convention that matches the CFC chart hierarchy (e.g., UNIT101/FC101/AI_TEMP_01). The convention short-circuits the manual tag-selection dialog and makes picture-to-CFC audits trivial.
6. Schedule transfers during plant downtime when the OS is running in test mode or a backup OS is hot. Transfers on a live, operating OS can cause momentary loss of picture updates and, in rare cases, disconnect redundant OS servers if the WinCC project file is replaced mid-cycle.
7. Maintain a transfer log. The V5.1 PLC-OS Transfer wizard can be invoked from a command-line wrapper for batch execution. Capture the output of every transfer to a project logbook; a delta from the previous run is the most reliable audit trail for tag changes.
8. Run an OS Compile at every major milestone — initial commissioning, every functional change, every AS firmware migration. An out-of-date OS picture DLL is the most common source of "transfer worked, but picture still does not update" follow-on issues.

Frequently Asked Questions