CPU 410-5H Memory Reset (MRES) and System Expansion Card (SEC) Process Object License Retention

Performing a Clear/Reset (MRES) on a SIMATIC PCS 7 CPU 410-5H controller clears the volatile work memory (RAM) and resets communication buffers, but DOES NOT delete or affect the Process Object (PO) licenses. On the CPU 410-5H, Process Object capacity (e.g., 100 to 2000+ POs) is permanently stored in non-volatile hardware flash memory on the physical System Expansion Card (SEC) inserted into the rear of the controller. Memory reset, power cycling, and firmware updates leave SEC licensing intact. Following an MRES, the CPU restarts in STOP mode, reads the licensed capacity from the SEC, and validates downloaded CFC process objects against this hardware entitlement.

Executive Summary

Process engineers and commissioning personnel frequently express concern that executing a CPU memory reset (MRES or 'PLC -> Clear/Reset...' in STEP 7 / HW Config) on a SIMATIC PCS 7 CPU 410-5H controller will erase purchased Process Object (PO) licenses, requiring costly re-licensing. Unlike traditional controllers where licenses were tied to battery-backed RAM or software memory cards, the CPU 410-5H implements a dedicated hardware licensing architecture centered on the System Expansion Card (SEC). This article confirms the non-volatile nature of SEC licensing during memory resets, details the underlying mechanics, and outlines safe reset and recovery procedures.

Architecture and Fundamental Mechanics

The SIMATIC S7 CPU 410-5H Process Automation controller employs an innovative scalable capacity model. The physical CPU hardware is identical across all performance classes; its operational capacity—specifically the maximum number of Process Objects (AS RT PO) and system performance limits—is dictated exclusively by the physical System Expansion Card (SEC).

The SEC is a specialized, tamper-proof cryptographic hardware module inserted into a dedicated slot on the CPU. License entitlements (ranging from base 100 PO packages up to 2000+ POs) are loaded onto the SEC using the Siemens Automation License Manager (ALM) via the CPU's engineering interface, or pre-commissioned from the factory.

Executing a Memory Reset (MRES) via the physical toggle switch or STEP 7 engineering command targets the CPU's internal volatile operating memory (RAM):
1. Clears work memory (user program logic, data blocks, dynamic instances).
2. Resets active communication buffers, S7 connections, and diagnostic buffers.
3. Preserves internal firmware and non-volatile parameter storage.
4. Crucially, the CPU operating system queries the SEC hardware register upon reboot. The licensed PO capacity remains permanently recorded on the SEC and is immediately restored. When a new program is downloaded, the CPU recalculates active PO consumption against the SEC limit.

Step-by-Step Implementation Procedure

Verify CPU 410-5H SEC Status Before Reset:
a. Open SIMATIC Manager and establish an online connection to the CPU 410-5H.
b. Select 'PLC -> Module Information' and navigate to the 'Performance Data' or 'Process Objects' tab.
c. Note the total licensed PO capacity granted by the SEC and current PO consumption.
Execute Memory Reset (MRES) via Hardware Switch:
a. Locate the mode selector toggle switch on the front panel of the CPU 410-5H.
b. Move and hold the switch in the 'MRES' position for approximately 3 seconds until the STOP LED flashes slowly.
c. Release the switch back to the 'STOP' position, then immediately (within 3 seconds) toggle back to 'MRES'. The STOP LED will flash rapidly, confirming memory reset execution.
d. When the STOP LED returns to a solid glow, the memory reset is complete.
Alternative: Execute Clear/Reset via STEP 7 / HW Config:
a. In SIMATIC Manager or HW Config, select the target CPU 410-5H.
b. Choose 'PLC -> Clear/Reset...'.
c. Confirm the prompt to reset the automation system memory.
Reconnect and Verify License Retention:
a. In SIMATIC Manager, select 'PLC -> Module Information'.
b. Confirm that the total licensed PO capacity on the System Expansion Card remains 100% intact and unchanged.
c. Download the complete hardware configuration and CFC charts to the CPU in STOP mode, then transition the mode switch to RUN.

Verification

Following MRES, open SIMATIC Manager online to the CPU: verify the STOP LED is steady and no hardware fault LEDs (EXTF/INTF) remain lit.
In 'PLC -> Module Information -> Performance Data / Process Objects', confirm the PO capacity matches the original SEC configuration.
Open the Automation License Manager (ALM) on the Engineering Station: connect to the CPU 410-5H target and confirm the SEC license container reports valid status.
Execute a full program download and switch the CPU to RUN: verify all CFC charts resume cyclic execution without licensing fault alarms.

Limitations and Operational Precautions

In redundant CPU 410-5H (fault-tolerant H-system) configurations, both controllers MUST contain System Expansion Cards with identically matched Process Object capacity; mismatched SEC limits will prevent redundant synchronization. While MRES does not affect the SEC, physically removing the SEC while the CPU is powered on will cause an immediate CPU STOP and hardware fault. Sizing and procurement of SEC capacity upgrades should be coordinated through an authorized Siemens distributor or the Siemens Industry Mall.

Engineer FAQ

Does firmware updating the CPU 410-5H erase the SEC PO license?

No. CPU firmware updates update the operating system flash memory and do not overwrite or modify the license blocks on the System Expansion Card.

Can a System Expansion Card be moved to a replacement CPU 410-5H?

Yes. If a CPU hardware failure occurs, you can unplug the SEC from the failed controller and insert it into a spare CPU 410-5H of identical type; all PO licenses transfer seamlessly with the physical card.

What happens if CFC compilation exceeds the SEC PO capacity?

The CPU 410-5H will allow a download of changes with a PO overrun warning for a temporary grace period, after which the CPU enters a license violation state and blocks further downloads until expanded via ALM.

Does an MRES delete the controller IP address?

If the CPU hardware configuration was loaded into internal load memory, the IP address is reloaded; however, performing a factory reset via SIMATIC Manager clears the IP address, requiring re-assignment via 'Edit Ethernet Node'.

How are PO upgrades applied to an active CPU 410-5H?

PO expansion packs are purchased and transferred to the CPU's SEC online via the Automation License Manager (ALM) without requiring a CPU stop or memory reset.