Understanding AS-Prefixed Structure Types in PCS 7 v8.1 and v8.2 AS/OS Compilation

In SIMATIC PCS 7 v8.1, v8.2, and later releases (paired with WinCC v7.3+), creating structure types in WinCC Tag Management with the Automation Station prefix (e.g., 'AS1/MotL' instead of generic 'MotL') is a documented product design feature, not an error or configuration bug. This architectural change decouples block structure definitions across controllers, allowing different AS stations in the same multi-project to run different library revisions or customized block interfaces simultaneously without triggering WinCC structure collisions during AS/OS compilation.

Evolution of Structure Type Management in SIMATIC PCS 7

In SIMATIC PCS 7, the AS/OS Transfer (executed via the Compile OS wizard) is the central mechanism that synchronizes Automation Station (AS) control logic with the Operator Station (OS) Human-Machine Interface (HMI).

When an engineer configures technological blocks in CFC (such as MotL, VlvL, or custom user function blocks), the compiler inspects all block parameters marked with the attribute { S7_m_c := 'true' }:
* In WinCC Tag Management, the compiler creates a Structure Type defining the schema of elements (e.g., booleans, status DWORDs, real setpoints, commands).
* For each individual block instance instantiated in CFC, WinCC generates a Structure Tag conforming to that Structure Type schema.
* Starting in PCS 7 V8.1 and continuing through V8.2, V9.0, V9.1, and V10.0 (coinciding with WinCC V7.3+), engineers noticed a dramatic change: structure types were no longer created globally under single names like MotL or M01. Instead, they appeared prefixed with the controller station name: AS1/MotL, AS2/MotL, or AS1/M01.

The Legacy Dilemma: Cross-Station Structure Collisions in PCS 7 <= v8.0

Understanding why Siemens introduced station-prefixed structure types requires examining the fatal architectural limitation of legacy versions (PCS 7 V7.0, V7.1, V8.0):

The Global Collision Problem:
In legacy versions, structure types were global to the entire OS project. If an enterprise facility operated ten S7-400 controllers (AS1 through AS10), all ten controllers shared a single WinCC structure type definition: MotL.
The Plant Upgrade Nightmare:
Suppose an engineer needed to upgrade Unit 1 (AS1) to a newer library hotfix or add a custom technological input pin to a motor block, while Units 2 through 10 remained untouched in active production.
The Compilation Disaster:
Running Compile OS for AS1 updated the global MotL structure type in WinCC. Because the structure type was shared globally, the new schema altered internal tag offsets for all other nine controllers.
When operators clicked motor faceplates on AS2 through AS10, WinCC read mismatched memory offsets, causing corrupted displays, bad quality codes, or system crashes. Engineers were trapped: they could never modify a block on one AS without recompiling and testing every controller in the plant.

The Modern Paradigm: Station-Specific Structure Types (AS/OS Transfer)

To resolve this multi-controller bottleneck, Siemens re-engineered the AS/OS compiler in PCS 7 V8.1 / WinCC V7.3:

Station Isolation:
The OS compiler automatically prepends the AS Station name to the structure type: <AS_Name>/<Block_Type>.
Independent Versioning:
AS1 can execute MotL with 45 internal tags (generating structure type AS1/MotL), while AS2 executes legacy MotL with 42 internal tags (generating structure type AS2/MotL). Both structure types coexist cleanly inside the WinCC tag database without interference.
System Product Feature:
This behavior is hardcoded into the PCS 7 OS compilation engine. It is not an error, nor is there a toggle setting to revert to legacy global structures, as doing so would reintroduce data corruption risks.

Impact on Block Icons, Faceplates, and Tag Management

Engineers frequently express concern that prefixing structure types with the AS name will break pre-existing WinCC graphics, block icons, or faceplate scripts:

Automated Block Icon Binding:
The OS compilation wizard automatically adapts block icon generation. When the compiler instantiates a block icon from @PCS7Typicals.pdl, it writes the full station-prefixed type into the icon's #type property (e.g., #type = @AS1/MotL/1).
Faceplate Script Neutrality:
Standard Advanced Process Library (APL) faceplate scripts (such as APL_OpenFaceplate) do not query the structure type name; they operate on the instance tag prefix (e.g., Plant1/Unit1/Motor101.). The internal WinCC tag engine resolves the underlying structure type transparently.
Seamless Migration:
When migrating an older project to V8.1 or V8.2, existing global structure types remain in Tag Management until the first Compile OS is executed. Upon compilation, the compiler purges unused legacy global types and establishes the new station-specific structures cleanly.

Comparison Table: Global Structure Types vs AS-Prefixed Structure Types

The following table details the architectural differences across PCS 7 versions:

Architecture MetricLegacy Global Structure Types (<= V8.0)Modern AS-Prefixed Structure Types (>= V8.1)Naming Convention<BlockType> (e.g., MotL, M01)<AS_Name>/<BlockType> (e.g., AS1/MotL, AS2/M01)System IntroductionPCS 7 V6.x, V7.x, V8.0 (WinCC <= V7.2)PCS 7 V8.1, V8.2, V9.x, V10.x (WinCC >= V7.3)Cross-AS Library MixingStrictly prohibited (causes collisions)Fully supported (independent per AS)Structure Collision RiskVery High during partial plant upgradesZero (complete namespace isolation)User ConfigurabilityStandard behaviorMandatory product feature (cannot be disabled)Block Icon BindingUses global type keysAutomatically handles AS-prefixed type keysEngineering ImpactRequires plant-wide block harmonizationPermits phased, unit-by-unit plant upgrades

Step-by-Step Procedure to Audit and Manage AS-Prefixed Structures

Follow this verified engineering workflow to inspect and audit structure types following an AS/OS transfer:

Perform AS/OS Compilation:
* In SIMATIC Manager, right-click the OS project > Compile.
* Advance through the wizard, ensuring all target AS stations are selected.
* Enable Create/update block icons and execute compilation.
Inspect WinCC Structure Types in Tag Management:
* Open the OS project in WinCC Explorer.
* Open Tag Management.
* In the navigation tree, expand Structure Types.
* Observe the naming structure: Confirm that structure types are organized as <AS_Name>/<BlockType> (e.g., SIMATIC_400(1)/MotL).
Verify Block Icon Type Mapping:
* Open a target process picture in Graphic Designer.
* Select a newly generated block icon and open Object Properties.
* In the property window, inspect the property #type:
Confirm that the wizard populated the station-prefixed type automatically (e.g., @SIMATIC_400(1)/MotL/1).
Purge Obsolete Unused Structures (Post-Migration):
* If legacy unprefixed structures from a pre-V8.1 migration remain orphaned in Tag Management, right-click the unused structure type and select Delete. WinCC will verify that zero tags are bound to the type before deletion.

Verification

Verify that station-specific structure types function flawlessly in runtime:
1. In WinCC Graphic Designer, verify that all block icons display correct dynamic values without yellow question marks or grayed overlays.
2. In WinCC Runtime, click block icons originating from different AS controllers; verify that faceplates for both AS1 and AS2 open instantaneously with identical operational controls.
3. Open WinCC Channel Diagnosis; verify that Named Connections channels for all AS stations report status "Ready" with 0 tag mapping errors.
4. Inspect <WinCC_Project>\Diagnostics\WinCC_Sys_01.log to confirm that no structure type mismatch warnings are logged.

Limitations and Operational Precautions

Do Not Attempt to Rename Structures Manually: Never attempt to strip the AS prefix manually in WinCC Tag Management. Renaming structure types severs internal relational links generated by the OS compiler and will corrupt subsequent delta compiles.
Custom Third-Party Scripts: If legacy custom C or VBS scripts directly evaluated the structure type name (e.g., querying GetTagTypeName), update the script string comparisons to accommodate the <AS_Name>/ prefix using wildcards or string-splitting functions.
Renaming Automation Stations: If an AS Station is renamed in SIMATIC Manager (e.g., changing AS1 to Boiler_AS), the next OS compilation will generate a brand new set of structure types (Boiler_AS/...) and reassign all instance tags. Recompile all process pictures to update block icon references.
Commercial Accuracy: Structure type generation is an automated engineering system feature governed by standard PCS 7 OS Engineering and Runtime licensing (6ES7658-2CX58-0YB5). Validate license allocations with an authorized Siemens distributor quotation.

Engineer FAQ

Can I disable AS-prefixed structure types and revert to global structures in PCS 7 v8.2?

No. The station-prefixed structure type architecture is an unconfigurable core system design feature implemented in WinCC V7.3 and PCS 7 V8.1+ to prevent cross-controller structure corruption.

Why did my migrated project show unprefixed structures initially before the first compile?

When an older project is migrated without compiling, WinCC retains the legacy database records. As soon as the first AS/OS transfer executes, the compiler rebuilds the database using modern station-prefixed architecture.

Does having AS-prefixed structure types increase WinCC Tag licensing costs?

No. WinCC licensing is based on the total count of Process Objects (PO) or Archive Tags, not on the number of structure type definitions in Tag Management.

How do custom user-defined Function Blocks behave during AS/OS transfer?

User-defined FBs with the { S7_m_c := 'true' } attribute behave identically to Siemens library blocks: the compiler automatically creates <AS_Name>/<UserFBName> structure types in WinCC.