Acquire a raw .img file that matches your exact MMC part number and size (e.g., 64KB, 128KB, 512KB, 2MB, 4MB, 8MB).
No. S7-300 CPUs require proprietary Siemens Micro Memory Cards (MMCs). Standard SD cards will not be recognized, and trying to use them may cause CPU errors. Why does my PLC keep asking for an MMC?
Put the card into a standard third-party laptop card reader.
Open the formatting tool. You should see a simple interface listing available drives. siemens mmc card format tool
In the world of industrial automation, Siemens is a titan. Their Simatic S7, C7, and WinAC controllers are the backbone of countless manufacturing plants, power grids, and transportation systems. A critical, yet often overlooked, component of these systems is the . These cards are not your average consumer SD cards; they act as the load memory for the PLC (Programmable Logic Controller), holding the operating system, user programs (OBs, FBs, DBs), and hardware configurations.
, you can format the card directly in the dedicated MMC slot. Critical Warnings Do Not Use Windows Tools
This method is the safest as it uses the official Siemens engineering software. Connect to your CPU and ensure it is in . Open the Online & Diagnostics view for the connected CPU. Acquire a raw
Pull the mode switch down to the (Memory Reset) position and hold it there for roughly 9 seconds until the STOP LED lights up permanently.
If the CPU still does not recognize the card, repeat the procedure with a different image source or consider using WinHex for a more precise sector‑by‑sector copy.
3️⃣
Select all blocks (Ctrl + A) and press , or navigate to PLC > Clear/Reset .
By mastering this tool, you can revive "dead" cards, safely prepare new media, and avoid the costly mistake of bricking a $150 memory card with a simple right-click.
The most popular freeware utility ecosystem developed by the automation community includes (S7 Image Read) and S7ImgWR (S7 Image Write). Standard SD cards will not be recognized, and
Explain how to back up your S7-300 program before resetting.