6ES7953-8LL31-0AA0 SIMATIC S7 Micro Memory Card

SKU: 6ES7953-8LL31-0AA0 Category: PLC

Description
Additional information

The Siemens SIMATIC S7 Micro Memory Card (MMC), part number 6ES7953-8LL31-0AA0, is a non-volatile flash memory card designed for use with SIMATIC S7-300 PLCs and related automation components. It belongs to the SIMATIC S7 memory card family and serves as the primary program and data storage medium for S7-300 CPUs, replacing the need for a battery-backed RAM in many applications. The card stores user programs, data blocks, and CPU parameters in a secure, non-volatile format.

The 6ES7953-8LL31-0AA0 variant provides 4 MB of flash memory storage capacity, making it suitable for larger S7-300 CPU programs and data-intensive applications. The card uses a compact MMC form factor and interfaces directly with the CPU's front-panel card slot without requiring any additional adapter. It retains data without a backup battery, supports firmware updates for compatible CPUs, and can also store recipe data, archiving data, and HTML pages for web-enabled CPUs. The card is write-protected against accidental erasure during normal CPU operation.

The SIMATIC S7 Micro Memory Card is widely used across manufacturing, process automation, and machine building industries wherever S7-300 PLCs are deployed. It is particularly suited for applications requiring reliable, battery-free program retention during power loss, such as conveyor systems, packaging machinery, press controls, and process plant automation. The card is also used during CPU replacement or firmware upgrades, allowing fast and reliable program transfer to a new CPU unit.

Technical Specifications

Memory Capacity	4 MB
Memory Type	Flash (non-volatile)
Form Factor	Micro Memory Card (MMC)
Compatible Systems	SIMATIC S7-300 CPUs, C7, ET 200 with CPU
Data Retention	Battery-free, non-volatile
Operating Voltage	3.3 V
Operating Temperature	0 °C to +60 °C
Storage Temperature	-20 °C to +85 °C
Relative Humidity	95 %, non-condensing
Series/Product Family	SIMATIC S7 Micro Memory Card
Certifications	CE, UL
Write Protection	Hardware write-protect switch

Common System Event Codes

Fault Code 129: Memory card not recognized or not inserted correctly by the CPU.
Remove and re-insert the Micro Memory Card. Ensure the card is fully seated in the CPU slot. Check for physical damage to the card contacts.
Fault Code 130: Memory card content is invalid or corrupted. CPU cannot load the program.
Re-download the user program from the programming device (PG/PC) to the Micro Memory Card using STEP 7. If the error persists, replace the card.
Fault Code 133: Memory card is write-protected during a program download attempt.
Check the write-protect switch on the side of the Micro Memory Card and set it to the write-enabled position before attempting to download.
Fault Code 137: Incompatible Micro Memory Card type detected for the inserted CPU.
Verify that the MMC part number is compatible with the specific S7-300 CPU variant in use. Replace with a compatible card if necessary.
Fault Code 141: Memory card capacity insufficient for the user program or data being transferred.
Use a Micro Memory Card with a larger storage capacity. Ensure the program size does not exceed the card's available memory.
Fault Code 121: CPU in STOP state due to missing or unreadable Micro Memory Card on startup.
Insert a valid, programmed Micro Memory Card into the CPU slot and perform a memory reset (MRES) before restarting the CPU.
Fault Code 126: Error during internal transfer of program from Micro Memory Card to CPU work memory (load memory transfer fault).
Perform a CPU memory reset (MRES), then re-download the user program. If the fault recurs, replace the Micro Memory Card.

Frequently Asked Questions

What is the storage capacity of the 6ES7953-8LL31-0AA0 Micro Memory Card?

The 6ES7953-8LL31-0AA0 provides 4 MB of non-volatile flash memory storage for user programs, data blocks, and CPU parameters.

Does this Micro Memory Card require a backup battery to retain data?

No. The MMC uses flash memory technology and retains all stored data without a backup battery, even during extended power outages.

Which Siemens PLCs are compatible with the 6ES7953-8LL31-0AA0?

This card is compatible with SIMATIC S7-300 series CPUs, C7 controllers, and ET 200 distributed I/O stations equipped with an integrated CPU that accept the standard MMC form factor.

Can the Micro Memory Card be used to transfer a program to a replacement CPU?

Yes. The MMC stores the complete user program and CPU parameters. Inserting the card into a replacement CPU of the same type and performing a memory reset will load the program automatically.

Is it possible to store data other than the user program on this card?

Yes. In addition to the user program and data blocks, the card can store firmware updates, recipe data, and HTML pages for web-enabled S7-300 CPUs, depending on the CPU variant used.

Troubleshooting

CPU enters STOP mode immediately after power-on with the MMC inserted

Check the CPU diagnostic buffer in STEP 7 (accessible via PG/PC online connection) for fault codes related to memory card errors. Verify the card is fully inserted and the write-protect switch is in the correct position.

Perform a CPU memory reset (MRES) by holding the mode selector switch in the MRES position for the required duration. Re-download the user program from STEP 7 to the MMC and restart the CPU.

STEP 7 cannot download the program to the Micro Memory Card

Check whether the write-protect switch on the MMC is enabled. Verify the online connection between the PG/PC and the CPU is established and that the correct CPU address is configured in STEP 7.

Slide the write-protect switch on the MMC to the unlocked position. Ensure the MPI or PROFIBUS connection is active and retry the download. If the card is not recognized, replace it with a new 6ES7953-8LL31-0AA0.

Program is lost after power cycle despite using the MMC

Confirm that the program was downloaded directly to the MMC (load memory) and not only to the CPU's internal RAM. Check STEP 7 download options to ensure the target is the memory card.

In STEP 7, select 'Download to module' and ensure the program is written to the load memory (MMC). The MMC must contain the program for it to persist across power cycles without a battery.

CPU does not recognize the newly inserted Micro Memory Card

Inspect the card slot and card contacts for contamination or physical damage. Verify the MMC part number is compatible with the CPU model in use.

Clean the card contacts gently with a dry, lint-free cloth. Re-insert the card firmly. If the CPU still does not recognize the card, test with a known-good MMC of the same type to determine whether the fault is with the card or the CPU slot.

Memory card read/write errors occur during CPU operation

Check the CPU diagnostic buffer for specific fault codes. Excessive read/write cycles can degrade flash memory cells over time. Verify the application is not writing to the MMC at an excessively high cycle rate.

Reduce the frequency of write operations to the MMC in the user program (avoid writing to the card in every scan cycle). If errors persist, replace the Micro Memory Card with a new 6ES7953-8LL31-0AA0.

Condition	Repair, Used, Refurbished, New in box (sealed)