Integrating Non-Released Standard S7-400 Controllers (CPU 412-2 PN) into SIMATIC PCS 7: APL and AS RT PO Rules

The Siemens standard S7-400 controller CPU 412-2 PN is not released for use as a SIMATIC PCS 7 Automation Station (AS). While individual Advanced Process Library (APL) function blocks can technically execute in the controller if programmed in CFC, the limited work memory (1 MB) and lack of communications resources on a CPU 412 severely restrict practical deployment. Furthermore, programming the CPU 412 in PCS 7 CFC will still consume AS Process Object (AS RT PO) licenses during download, because PO counting is enforced by the PCS 7 engineering compiler regardless of CPU model. To integrate a CPU 412-2 PN package unit into PCS 7, connect it as an external package unit using the PCS 7 Industry Library (IL) or standard S7 communication blocks (BSEND/BRCV).

Released Controller Baseline in SIMATIC PCS 7 Architectures

SIMATIC PCS 7 is a tightly coupled process control system designed for high availability, deterministic execution, and seamless diagnostic transparency. To guarantee these runtime characteristics, Siemens officially tests and releases only specific central processing units:

Dedicated PCS 7 Controller: CPU 410-5H Process Automation (and specialized derivatives CPU 410 SMART / CPU 410E).
Standard S7-400 High-Capacity Controllers: CPU 414-3, CPU 416-2/3, CPU 417-4.
Fault-Tolerant S7-400H Controllers: CPU 414-4H, CPU 417-4H.

Entry-level standard controllers from the factory automation portfolio—specifically the CPU 412-1 and CPU 412-2 PN—are explicitly not released for SIMATIC PCS 7. Incorporating an unreleased CPU into a PCS 7 project introduces severe architectural constraints and voids standard technical support guarantees.

Technical Constraints of the Standard S7-400 CPU 412-2 PN

The exclusion of the CPU 412-2 PN from PCS 7 is driven by physical hardware bottlenecks:

Severely Constrained Work Memory: The CPU 412-2 PN features only 1.0 MB of integrated work memory (expandable up to only 1.5 MB). In contrast, released PCS 7 controllers provide between 4 MB and 48 MB (CPU 410-5H). A standard PCS 7 baseline program with system OBs and driver libraries consumes over 500 KB before a single control loop is created.
Communication & PBC Buffer Limits: PCS 7 relies on Parameter and Block Change (PBC) communication buffers and high-density ALARM_8P queues. The CPU 412-2 PN lacks the connection resources to service redundant OS servers, engineering stations, and batch clients simultaneously.
Module Driver Generation: The PCS 7 compiler utility 'Generate Module Drivers' does not contain hardware abstraction rules for entry-level CPUs, generating compilation errors when linking ET 200 distributed peripherals.

Can APL Function Blocks Execute on a Non-Released CPU 412?

From a pure instruction-set perspective, APL blocks (such as PIDConL, MotL, VlvL) are compiled S7 Function Blocks (FBs). If an engineer manually copies APL blocks into an S7 program on a CPU 412-2 PN:

The blocks can execute mathematically within controller RAM.
However, each APL block has a massive instance memory footprint: a single PIDConL instance DB consumes several kilobytes of RAM. In a CPU with only 1 MB work memory, the controller exhausts memory after creating fewer than 20 to 30 technological loops.
Essential APL supervisory functions—such as automatic diagnostic generation (Pcs7AnIn, MOD_D1) and maintenance station linking—will fail.

AS Process Object (AS RT PO) License Accounting Enforced on Non-Released Hardware

Engineers frequently assume that using a standard 'non-PCS 7' PLC will bypass Siemens Process Object licensing fees:

Process Object licensing is enforced by the PCS 7 Engineering System (CFC Compiler and ALM), NOT by the physical controller hardware.

When an engineer compiles and downloads CFC charts from a PCS 7 Engineering Station:

The compiler parses all blocks bearing the attribute S7_m_c := 'true' (Operator Control & Monitoring capability).
The compiler calculates the total Process Object count.
During download, the ES queries Automation License Manager (ALM) and deducts the required AS RT PO licenses from the engineering station's pooled license key.
Downloading to a CPU 412-2 PN will consume AS RT PO licenses identically to a released CPU. If PO licenses are insufficient, ALM records a license debt.

Comparative Architecture Matrix: Released PCS 7 CPUs vs Standard S7-400

The following table compares technical specifications between controllers:

Technical DimensionCPU 412-2 PN (Standard STEP 7)CPU 414-3 / 416-3 (Standard PCS 7)CPU 410-5H (Dedicated PCS 7)Siemens PCS 7 ReleaseNOT RELEASEDOfficially ReleasedOfficially Released (Flagship)Integrated Work Memory1.0 MB4.0 MB to 16.0 MBUp to 48 MB (Dynamic SEC Sizing)AS RT PO License DeductionYes (If downloaded from ES)YesYes (Hardware SEC + Software ALM)Generate Module DriversIncompatible; driver errorsFully SupportedFully SupportedOnline Changes in RUN (CiR)Extremely LimitedFully SupportedHigh-Speed Online Changes in RUNPrimary ApplicationSmall standalone machine automationMedium-to-large process cellsDCS, High-Availability, & F-Safety

Recommended Architectural Integration for Package Units

If a vendor delivers a skid or package unit controlled by a CPU 412-2 PN, do not attempt to force it into the PCS 7 AS hierarchy. Instead, integrate it using the standard Package Unit Architecture:

Decoupled Engineering: Maintain the CPU 412-2 PN in a separate standard STEP 7 V5.x or TIA Portal project.
Communication Linkage: Configure a native S7 connection in NetPro over Industrial Ethernet. Use coordinated communication blocks (BSEND/BRCV or PUT/GET) to exchange process handshakes with the primary PCS 7 controller.
PCS 7 Industry Library (IL): Utilize the Siemens PCS 7 Industry Library package unit blocks (IL_S7 / Panel) to map skid data cleanly into WinCC OS faceplates without violating PCS 7 controller baselines.

Verification

Verify architectural boundaries and license consumption:

In SIMATIC Manager on the Master ES, open Options -> Process Objects -> Available Licenses. Record the current AS RT PO balance.
If a test CFC containing APL blocks is compiled and downloaded to the CPU 412-2 PN, re-open the Available Licenses dialog; confirm that PO consumption has increased.
In HW Config, verify whether module driver generation flags errors on unreleased peripheral modules.
Confirm that S7 communication blocks (BSEND/BRCV) transfer process data reliably between the package unit and the master DCS.

Limitations and Operational Precautions

Adhere to the following architectural precautions:

No Manufacturer Support for Unreleased AS: Siemens Customer Support will not troubleshoot system crashes, driver generation failures, or timing overruns on PCS 7 systems running on CPU 412 controllers.
Work Memory Exhaustion: Never attempt to run APL faceplates or large continuous process plants on CPU 412 hardware; memory exhaustion will cause CPU STOP during delta compilation.
Commercial License Audit: Understand that using standard controllers does not reduce software licensing costs; always factor AS RT PO entitlements into procurement schedules.

[!NOTE]
Commercial Accuracy Disclaimer: Software order numbers (MLFBs), package structures, and hardware capacity prerequisites vary across PCS 7 versions > and hardware platforms. System integrators must confirm exact software entitlements and licensing requirements against the official Siemens > Catalog CA 01 and obtain an authorized Siemens distributor quotation prior to purchasing.

Engineer FAQ

Can individual APL blocks execute inside a CPU 412-2 PN?

Yes, the S7-400 CPU can physically execute the block instructions, but its small 1 MB work memory will be exhausted after only a few technological control loops.

How should a CPU 412-2 PN package unit be connected to a PCS 7 plant?

Integrate it as an external package unit using S7 communication blocks (BSEND/BRCV) or the PCS 7 Industry Library, rather than treating it as an internal PCS 7 Automation Station.

What S7-400 CPUs are officially released for SIMATIC PCS 7?

Released controllers include the dedicated CPU 410-5H Process Automation, standard high-capacity CPUs (CPU 414-3, CPU 416-2/3, CPU 417-4), and fault-tolerant CPUs (CPU 414-4H, CPU 417-4H).