Using generic "MMC Format" tools found on the internet is dangerous. They often format the card to FAT16, which allows a PC to read it, but the S7-300 CPU will reject it (Result: SF LED flashing, STOP mode).
Siemens officially states that end users cannot "format" an S7-300 MMC. The only user-permissible action is a "reset," which deletes all user data but retains the proprietary Siemens structure. This reset is performed via the CPU itself using the following official procedure:
Key features
Option A: Using a Siemens PG (Programming Device) or USB Prommer siemens mmc card format tool
The you are using (e.g., S7-300, S7-1200, S7-1500). If the card is currently unreadable or "defective." If you have a Siemens USB Prommer or a Field PG.
What or Siemens PG laptop you have available.
If a card has already been accidentally formatted in Windows, Siemens officially considers it non-recoverable. However, the automation community has developed unofficial workarounds: Using generic "MMC Format" tools found on the
Summary
Before diving into the specific tool, it is crucial to understand why you cannot use Windows Explorer or SD Formatter on a Siemens MMC.
Help identify the correct part number for a replacement MMC. The only user-permissible action is a "reset," which
If an MMC has been accidentally formatted in Windows or become unrecognizable to the CPU, the following recovery method has proven effective for many users:
The CPU cannot function without the MMC. If it is flashing "Stop," "Defective," or showing no program, the card may be missing, poorly seated, or corrupted. The MRES process does not work. What now?
Right-click the S7ImgWR.exe tool and choose "Run as Administrator."
Here's a step-by-step guide to formatting an MMC card using the Siemens tool: