The safest and most reliable way to format or clear a Siemens MMC is through official Siemens software. This method ensures that the card's master boot records and structural integrity remain intact. How to Format via TIA Portal or STEP 7 V5.x
Verdict (concise)
This is the safest method, ensuring the PLC creates the correct structure. Put your CPU into STOP mode. Insert MMC: Insert the MMC into the slot on the S7-300 CPU. Power On: Power on the PLC. Reset via Switch: siemens mmc card format tool
Insert the Siemens MMC into the PG card slot or USB Prommer. Open or STEP 7 Manager .
Insert the MMC into a standard multi-card reader (Note: some modern USB 3.0 readers block raw commands; older internal or USB 2.0 readers often work best). Run the tool as an Administrator. The safest and most reliable way to format
Insert the working MMC into a standard MMC/SD card reader connected to a Windows PC. Launch S7ImgRD.exe , select the drive letter corresponding to the MMC, and save a complete image file (typically with the extension .S7img or .bin ).
Do not use right-click format in Windows Explorer, and do not use standard disk management tools. If your PC prompts you to format the card upon insertion, always select . Put your CPU into STOP mode
Routine maintenance and clearing old PLC projects. 2. TIA Portal
I can provide the specific step-by-step recovery workflow for your equipment. Share public link
The STOP LED will flash rapidly, indicating the CPU is formatting the MMC back to its default internal structure. 2. Third-Party Siemens MMC Format & Image Tools