Description
The Siemens 6ES7953-8LJ30-0AA0 is a proprietary 512 KB Micro Memory Card (MMC) designed for use with SIMATIC S7-300 CPUs and ET 200 distributed I/O systems. Unlike standard consumer-grade SD cards, this MMC is specifically formatted to hold the S7 project data (blocks, hardware configuration, and force values) and is required for the operation of most modern S7-300 central processing units.
Availability and Procurement
- Condition: New Original (Factory Sealed) or Refurbished (Tested/Cleared)
- Warranty: 12-month standard industrial warranty
- Lead Time: Typically in stock; same-day or next-day shipping available
- Pricing: Market-driven due to the legacy status of some S7-300 components; contact us for a firm quote.
Technical Specifications
This card is built to industrial endurance standards, capable of handling the high-frequency read/write cycles required for Retentive Data storage in a PLC environment.
| Parameter | Specification |
| Memory Capacity | 512 KB |
| Type | Flash-EPROM (MMC) |
| Minimum Write/Erase Cycles | 100,000 |
| Data Retention | 10 years after final programming |
| Compatibility | S7-300 CPUs, ET 200S (IM151-7/8), ET 200pro (IM154-8) |
| Dimensions | 24 mm x 32 mm x 1.4 mm |
| Weight | Approximately 2 g |
Engineering Insights: Usage and Constraints
As an architect who has recovered countless systems from “Stop” mode, I advise strict adherence to the following technical constraints regarding this module:
1. The “Never Format” Rule
CRITICAL: Never insert this card into a standard Windows PC and format it using Windows Explorer. Doing so destroys the internal Siemens-specific partition and hidden block structure. Once formatted by a standard OS, the card becomes invisible to a Siemens CPU and is effectively e-waste. To read or write via PC, you must use a dedicated Siemens Field PG or the USB Prommer (6ES7792-0AA00-0AA0).
2. Sizing and Capacity (512 KB)
The 512 KB capacity is the “middle ground” for S7-300 applications.
- Suitability: Ideal for medium-sized logic programs and hardware configurations.
- Risk: If your project involves extensive use of Data Blocks (DBs) for recipe storage or historical trending, you may exceed the 512 KB limit. Always check the “Object Properties -> Statistics” in STEP 7 or TIA Portal to verify the “Load Memory” requirement before purchasing.
3. CPU Operation Without MMC
Modern S7-300 CPUs (those with a width of 40mm or less) will not run without an MMC inserted. The MMC acts as the Load Memory; without it, the CPU has no program to execute after a power cycle.
4. Maintenance and Replacement
If a CPU reports a “Memory Card Error” (STOP LED flashing slowly), verify the card is seated correctly. In high-vibration environments, the contacts can oxidize. Clean them with an electronics-grade cleaner—do not use abrasives.
FAQ
Q: Can I use a larger card, like a 2 MB or 4 MB, if the 512 KB is out of stock?
A: Yes. You can always go up in size (e.g., replace a 512 KB card with a 2 MB card). The CPU will simply address the extra space as available Load Memory. However, you cannot downgrade if your project size exceeds the smaller card’s capacity.
Q: How do I clear the card if I don’t have a Siemens Prommer?
A: Use the CPU’s MRES function. Insert the card into the CPU, turn the mode switch to MRES and hold until the STOP LED lights up, release, and quickly turn to MRES again. This resets the card to factory settings using the PLC’s internal firmware.
Q: Is this card compatible with S7-1200 or S7-1500 PLCs?
A: No. S7-1200/1500 systems use the SMC (SIMATIC Memory Card), which is physically similar to an SD card. The 6ES7953 series is electrically different and only works with the S7-300/ET 200 legacy product lines.
| Siemens 6ES7417-4HL04-0AB0 – S7 |
| Siemens6SE7027-2TD61-Z |
| Siemens 1FK7060-2AF71-1RA0 |
