If you format a Siemens MMC using Windows (FAT/FAT32), the card's partition table is overwritten. The PLC will no longer recognize it as a Siemens card, and it often cannot be recovered.
💡 If the tool cannot read the card at all, try a different card reader. Some modern generic USB readers struggle with the proprietary format of Siemens industrial cards. siemens mmc card format tool
The most "official" way to format a card is through the Siemens programming software itself. If you format a Siemens MMC using Windows
Siemens SIMATIC Micro Memory Card (MMC) is a cornerstone of industrial automation, specifically for Siemens S7-300 and S7-400 PLC series Some modern generic USB readers struggle with the
Siemens MMC Card Format Guide: Tools and Techniques Formatting a Siemens Micro Memory Card (MMC) is a delicate process because these cards use a proprietary filesystem. Using standard Windows formatting tools often renders the card unusable by the PLC because it destroys the hidden Siemens-specific header information. Industrial Monitor Direct Recommended Tools and Official Methods