Understanding CPU 410-5H Hardware Capacity, System Expansion Cards (SEC), and Process Object Limits

In SIMATIC PCS 7 architectures utilizing the CPU 410-5H controller, system capacity is governed by three distinct dimensions: physical hardware I/O address capacity, work memory utilization, and software licensing via the System Expansion Card (SEC). While the CPU 410-5H hardware architecture supports approximately 7,500 physical field I/O signals across PROFIBUS DP and PROFINET IO (16 KB each for inputs and outputs), the actual functional capacity is scaled and authorized by the SEC hardware card (ranging from 100 POs to an unlimited SEC 2K+ package). Final licensing and memory headroom must always be validated against official Siemens catalogs and an authorized distributor quotation.

CPU 410-5H Hardware Architecture vs Software Process Objects

The SIMATIC PCS 7 CPU 410-5H (6ES7410-5HN08-0AB0) introduces an all-in-one hardware platform designed to cover the entire performance spectrum of process automation. Unlike legacy S7-400 modular controllers (where purchasing different CPU models—such as CPU 414, 416, or 417—was necessary to scale performance), every CPU 410-5H possesses identical high-performance computing hardware:
- Physical I/O Memory Address Space: 16 KB for inputs and 16 KB for outputs, supporting approximately 7,500 physical I/O channels across redundant PROFINET IO and PROFIBUS DP fieldbuses.
- Microprocessor Speed: High-performance dual-core processor capable of executing complex APL control algorithms at cycle times down to 10 ms.
- Process Objects (PO) Principle: In PCS 7, capacity is not measured strictly in physical I/O pins. A Process Object represents a technological function block (e.g. motor, valve, PID loop) possessing operator control or alarm capabilities, regardless of how many digital or analog signals it encapsulates.

System Expansion Card (SEC) Sizing and Expansion Options

The computing capacity and allowable Process Object count of the CPU 410-5H are unlocked by a plug-in hardware token called the System Expansion Card (SEC), inserted into the rear of the CPU:

Initial SEC Bundles: Sized based on plant requirements (e.g. SEC 100 PO, SEC 500 PO, SEC 1000 PO, SEC 1600 PO, and SEC 2000+ PO / Unlimited).
SEC 2K+ (Unlimited Capacity): For large installations requiring 2,000 POs or more, the SEC 2000+ (6ES7653-2CC00-0XB0) unlocks the maximum processing authorization of the controller.
Cumulative PO Expansion (CPU 410 Expansion Packs): Plant capacity can be upgraded online in increments of +100 or +500 POs using software license keys loaded via Automation License Manager (ALM) without replacing physical hardware.

Work Memory Constraints and High-Availability Headroom

While an SEC 2K+ removes software PO throttling, the physical controller execution boundary is bounded by Work Memory:
- Total Work Memory: The CPU 410-5H features 32 MB of integrated work memory (split equally: 16 MB for program code and 16 MB for data blocks). No external RAM memory cards are required.
- Redundancy Headroom Guidelines: In high-availability redundant systems (S7-410-5H pair), Siemens best-practice guidelines recommend maintaining work memory utilization below 60% to 70%.
- Online Changes Reserve: Sufficient memory headroom is required to buffer delta compilations during bumpless online downloads. Attempting to run 2,700 high-density technological blocks on a single CPU may exceed 80% work memory, increasing cycle times and risking download aborts.

Controller Capacity and Licensing Schedule Table

The following table details typical SEC capacities and technical specifications for the CPU 410-5H:

System Expansion Card (SEC)Licensed AS PO CapacityOrder Number (MLFB)Recommended Typical Plant SizeWork Memory LimitSEC 100 PO100 Process Objects6ES7653-2CA00-0XB0Small package units / skids32 MB Total (Code + Data)SEC 500 PO500 Process Objects6ES7653-2CB00-0XB0Standard process unit operations32 MB Total (Code + Data)SEC 1000 PO1,000 Process Objects6ES7653-2CD00-0XB0Medium plant area32 MB Total (Code + Data)SEC 1600 PO1,600 Process Objects6ES7653-2CE00-0XB0Large multi-unit operations32 MB Total (Code + Data)SEC 2K+ (Unlimited)2,000+ Process Objects6ES7653-2CC00-0XB0Centralized plant controller32 MB Total (Code + Data)SEC Expansion Pack (+100 PO)+100 PO Cumulative6ES7653-2CA01-0XB0Incremental plant expansionSoftware authorization

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.

Verification

Verify CPU 410-5H capacity and PO consumption:
1. In SIMATIC Manager, right-click the AS project and select Options > Process Objects > Calculate Process Objects to confirm required PO capacity.
2. In HW Config, double-click the CPU 410-5H and open the Module Information dialog; verify under the License tab that the installed SEC card matches or exceeds the required PO count.
3. Open the Memory tab in Module Information; verify that Work Memory (Code and Data) utilization is below 70%.
4. Inspect the controller cycle time under Performance; ensure average OB cycle time remains comfortably within target task bounds (e.g. <30 ms in OB35).

Limitations and Operational Precautions

Essential rules when planning CPU 410-5H architectures:
- The CPU 410-5H will not transition to RUN mode if the physical SEC card is missing, defective, or improperly seated in the rear slot.
- Operating an S7-410H redundant pair requires two identical SEC cards with identical PO capacities.
- For plants exceeding 2,000 POs or 2,500 signals, consider splitting the process across two separate controller pairs to distribute CPU load and optimize failure domains.

Engineer FAQ

Does the CPU 410-5H require external memory cards (RAM/Flash)?

No. The CPU 410-5H incorporates 32 MB of non-volatile integrated work memory; external memory cards are obsolete on this platform.

Can I upgrade the SEC capacity without shutting down the plant?

Yes. Using the CPU 410 Expansion Pack workflow and Automation License Manager, PO capacity can be expanded online without stopping controller execution.