If your card was mistakenly formatted by Windows, Siemens software will no longer recognize it. In this scenario, automation engineers turn to third-party sector-imaging tools to write a clean, raw image back to the card. 1. S7ImgRD and S7ImgWR (By RunMode)
A common point of confusion involves the naming and physical appearance of Siemens memory cards. The cards used in S7-300 CPUs are , recognizable by their turquoise color . The newer S7-1200 and S7-1500 CPUs use SMC (SIMATIC Memory Card) , which are black and function differently. The recovery methods and tools described in this article are specific to the MMC (turquoise) cards used with S7‑300 systems.
The safest way to clear a Siemens MMC is through official engineering software. This requires an official Siemens field utility device (Field PG) or a specialized Siemens USB Prommer. Steps for STEP 7 Classic: Insert the MMC into your PG or USB Prommer slot. Open . →right arrow S7 Memory Card →right arrow Open . Select all blocks on the card. Right-click and choose Delete (or use the Delete key). Steps for TIA Portal: Open your project in TIA Portal . Expand the Project Tree on the left. Locate and expand Card Reader/USB memory . Select your specific Siemens card reader slot. Right-click the MMC and select Format . Method 2: The PLC Hardware Slot Method (No Software Needed)
The software will safely wipe the data while protecting the system files. Method 3: Use a Prommer (External USB Card Reader) siemens mmc card format tool
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:
Browse and select a clean image file ( .img ) corresponding exactly to your card's size (e.g., a 64KB image for a 64KB card, 512KB for a 512KB card).
Here are the safe methods to clear and format your card using standard Siemens software or special hardware. Method 1: Use a Siemens PLC (The Safest Way) If your card was mistakenly formatted by Windows,
The safest way to format or reset a Siemens MMC is through official Siemens software or directly via the PLC hardware.
Proper management of your Siemens MMC is critical for maintaining uptime in automated systems. Using the (via MRES or TIA Portal) is the only authorized way to maintain the correct internal file structure. Avoid third-party formatting tools in Windows to prevent permanent damage to these specialized memory devices. If you're interested, I can:
Formatting should be a last resort. Here are best practices to keep your MMCs healthy: S7ImgRD and S7ImgWR (By RunMode) A common point
Within 3 seconds, press and hold the switch back down to the position again.
A Siemens Field PG a dedicated USB Prommer (such as the Siemens 6ES7792-0AA00-0XA0). Note: Standard PC multi-card readers cannot be used with STEP 7/TIA Portal for this specific operation. Step-by-Step for STEP 7 (Classic):
The card is now "empty" from a PLC perspective. It has no operating system or user program. If you insert this into a PLC, the CPU will likely show "No program" or request a firmware update (depending on the CPU model).