Siemens 6ES7951-0KG00-0AA0 MMC Module – SIMATIC S7-300

Siemens 6ES7951-0KG00-0AA0 — Non-Volatile Program Storage for SIMATIC S7-300 Control Architectures

The 6ES7951-0KG00-0AA0 is a 64 KB Micro Memory Card (MMC) manufactured by Siemens AG for exclusive use within the SIMATIC S7-300 programmable logic controller platform. Its primary function within a control loop is deterministic, battery-free program persistence: the CPU copies its user program, data blocks, and system parameters from the MMC into internal work RAM at every cold restart, ensuring that the controller resumes its last-known operational state without manual intervention or external backup media. In process-critical environments — continuous chemical dosing, conveyor sequencing, or multi-axis coordinated motion — this behavior eliminates the single-point failure mode introduced by battery-backed SRAM, which degrades over a 3–5 year service cycle and requires scheduled replacement.

At the architectural level, the MMC interfaces with the S7-300 CPU through a proprietary low-voltage serial bus embedded in the CPU’s front-panel card slot. The bus operates at 3.3 V logic levels and uses a synchronous read/write protocol managed by the CPU’s internal memory controller. Write cycles are initiated only during program download or firmware update operations; during normal PLC scan execution, the MMC is read-only, which eliminates write-wear as a reliability concern in steady-state production. The 64 KB capacity of the 6ES7951-0KG00-0AA0 accommodates user programs up to approximately 48 KB of compiled STL/LAD/FBD code, with the remaining address space reserved for data block storage and system diagnostics headers.

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Technical Parameters

Hardware Logical Analysis

The 6ES7951-0KG00-0AA0 employs NOR Flash memory architecture rather than the NAND Flash used in consumer SD cards. NOR Flash provides byte-addressable random reads with access latencies in the sub-microsecond range, which is essential for the CPU’s memory controller to execute a full program load into work RAM within the cold-restart timing window defined by the S7-300 watchdog. NAND Flash, by contrast, requires page-level reads and introduces variable latency that would be incompatible with the deterministic startup sequencing of the S7-300 platform.

From an EMC standpoint, the MMC card slot on S7-300 CPUs is shielded by the CPU’s metal front-panel housing, and the card’s internal traces are kept short enough that radiated emissions from the serial bus remain well below the EN 55011 Class A industrial limits. The card itself carries no active components beyond the Flash array and a minimal interface logic cell, which means it contributes negligible conducted noise to the CPU’s internal power rail. This passive architecture also means the card draws no standby current when the CPU is powered down, unlike battery-backed SRAM modules that maintain a continuous trickle drain.

The proprietary card format — physically distinct from standard MMC or SD specifications — is an intentional design constraint by Siemens. It prevents accidental insertion of consumer-grade Flash media, which would lack the industrial temperature rating and write-endurance specification required for 24/7 PLC operation. The card’s gold-plated contact pads are rated for a minimum of 1,000 insertion/extraction cycles, supporting routine program updates and field maintenance without contact degradation.

Firmware update capability is a secondary but operationally significant function. When a CPU firmware image is placed on the MMC and the CPU is cold-started with the card inserted, the bootloader detects the firmware file by its header signature and initiates a self-update sequence before loading the user program. This mechanism allows field engineers to update CPU firmware without a laptop or STEP 7 connection, reducing on-site service time in remote installations.

System Integration Benefits

• Battery elimination: Removes the 3–5 year battery replacement cycle from the maintenance schedule, reducing lifecycle cost and eliminating the risk of program loss from a depleted backup battery.
• Deterministic cold-restart behavior: The CPU loads the program from MMC into work RAM in a fixed, repeatable sequence, ensuring consistent startup timing across all power cycles — critical for synchronized multi-axis or multi-PLC systems.
• Firmware field-upgrade path: Engineers can deploy CPU firmware updates by writing the image to the MMC and performing a cold restart, without requiring a STEP 7 workstation on-site.
• Program portability: The MMC can be extracted from one CPU and inserted into an identical replacement unit, transferring the complete program and configuration in under 60 seconds — a significant advantage during emergency hardware swap-outs.
• Diagnostic transparency: STEP 7 and TIA Portal can read the MMC’s program checksum and version header, allowing engineers to verify that the installed program matches the engineering baseline without downloading a full comparison.
• Reduced wiring complexity: Because the MMC provides non-volatile storage natively, there is no need for external EEPROM modules or UPS-backed SRAM expansion cards in standard S7-300 configurations.
• Scalable capacity path: The 6ES7951-0KG00-0AA0 occupies the same physical slot as all other S7-300 MMC variants (32 KB through 4 MB), allowing a capacity upgrade without any mechanical or wiring changes to the control cabinet.
• Industrial temperature compliance: Rated for 0 °C to +60 °C continuous operation, covering the full ambient range of standard industrial enclosures without derating.
• Write-protect discipline: The CPU enforces read-only access to the MMC during normal scan execution, preventing accidental program corruption from software faults or communication errors during runtime.
• Long-term availability: As a standard SIMATIC S7-300 consumable, the 6ES7951-0KG00-0AA0 has been in continuous production for over two decades and remains available through authorized distribution channels for installed-base maintenance.

Quality Assurance & Global Logistics

Every unit of the 6ES7951-0KG00-0AA0 supplied through siemensplc.com is sourced from verified Siemens-authorized distribution channels or authenticated surplus stock with full traceability documentation. Each card undergoes a functional verification procedure prior to shipment: the card is inserted into a compatible S7-300 CPU, a test program is downloaded via STEP 7, and a cold-restart cycle confirms successful program retention and reload. Cards that fail any step of this procedure are quarantined and not shipped.

Packaging is inspected for Siemens holographic authenticity markings and tamper-evident seals before dispatch. Batch records — including lot number, date code, and test results — are retained for a minimum of three years and are available on request for MRO procurement teams and OEM quality audits.

Logistics operations are based in Xiamen, China, a major export hub with direct access to international freight carriers including DHL Express, FedEx International Priority, and UPS Worldwide Expedited. Standard in-stock orders are dispatched within 1–2 business days. Express delivery to most destinations in Southeast Asia, Europe, and North America is achievable within 3–7 business days. All shipments include a commercial invoice, packing list, and certificate of origin. Export compliance is verified against ECCN classifications and applicable dual-use regulations prior to each shipment. Customs documentation is prepared to minimize clearance delays at destination ports.

A 12-month warranty covers all units against manufacturing defects and functional failure under normal operating conditions. Warranty claims are processed with a target response time of 48 hours, and replacement units are dispatched from Xiamen stock upon claim approval.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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