S7-1200 CPU 1212C Firmware Update: SIMATIC MC 24MB Card Guide

Overview

The SIMATIC S7-1200 CPU 1212C (order numbers 6ES7212-1AD30-0XB0 and 6ES7212-1BD30-0XB0) requires a Siemens-supplied SIMATIC MC 24 MB memory card to perform an operating-system (firmware) update. Standard SD cards — even when partitioned or formatted to 24 MB — will not be accepted by the bootloader as a valid update medium. This reference documents the exact procedure, the hardware prerequisites, the firmware files, and the known failure modes observed in the field.

Affected CPU Variants and Order Numbers

Only the listed 1212C variants in the table below support the SIMATIC MC 24 MB firmware-update workflow described in this article. Always confirm the order number on the CPU's front label and match it to the firmware bundle on Siemens Industry Online Support.

Both variants use the same SIMATIC MC 24 MB card and the same update file layout; only the firmware bundle differs.

Prerequisites

1. SIMATIC MC 24 MB memory card (Siemens 6ES7954-8LF02-0AA0 or equivalent current revision). The card ships pre-formatted with a Siemens vendor signature in sector 0.
2. Windows PC with an SD-card slot or USB card reader.
3. Firmware update file downloaded from Operating system updates for CPU 1212C. The file is delivered as a self-extracting .exe that contains the .S7FW image.
4. CPU 1212C powered down (24 V DC or 120/230 V AC depending on variant).
5. Network access to support.industry.siemens.com for firmware and release notes.

Why a Third-Party SD Card Fails

The S7-1200 bootloader inspects the card during power-up before any user files are read. Specifically, the bootloader verifies:

• Vendor signature in the card's CID/MBR region that identifies the media as a Siemens SIMATIC MC.
• Pre-formatted image that contains the 24 MB FAT partition layout Siemens uses for program and firmware storage.
• Card capacity — the bootloader in firmware V2.x accepts only the 24 MB card; cards with 2 GB, 4 GB, or larger capacities (even if partitioned to 24 MB) are rejected.

Field reports confirm that partitioning a 2 GB SD card to a primary 24 MB FAT16 partition and writing the .S7FW file to the root does not initiate the update. The CPU either ignores the card or raises the ERROR LED. This is a deliberate design choice to protect the CPU from corrupted or counterfeit update media.

Preparing the SIMATIC MC 24 MB

1. Insert the SIMATIC MC 24 MB into the PC's SD card reader.
2. Double-click the downloaded firmware update .exe (for example CPU_1212C_V2.2.exe). The self-extractor opens a wizard.
3. Click Next, accept the license, and set the destination path to the root directory of the SIMATIC MC card (typically D:\ or the drive letter assigned to the card reader).
4. Confirm the extraction. The card now contains one file: S7_JOB.S7S and a firmware .S7FW file (for example FWUPDATE.S7FW).
5. Safely eject the card from the operating system before removing it from the reader.

Performing the Firmware Update on the CPU

1. Power down the CPU 1212C. The SD slot is on the underside/front of the module behind the lower door.
2. Open the card door and insert the prepared SIMATIC MC 24 MB with the labeled side facing up until it clicks.
3. Apply 24 V DC (or 120/230 V AC for the relay variant) to the CPU's power terminals L+ / M (or L1 / N).
4. Observe the LED pattern:
   • STOP flashing yellow — the bootloader is reading the .S7FW image.
   • RUN/STOP flashing alternately with ERROR — the update is in progress. Do not remove power.
   • STOP solid yellow — update complete.
5. The update typically takes 30–120 seconds. When the STOP LED becomes solid, the new firmware is active.
6. Power down the CPU again and remove the SIMATIC MC if you do not want it to remain in the slot as a transfer card.

Verification

1. Connect the CPU's PROFINET port to the TIA Portal engineering station.
2. In TIA Portal, open the project, right-click the CPU in the device tree, and select Online & Diagnostics > Diagnostics > Module Information.
3. Confirm the Firmware field now displays the target version (for example V2.2.0).
4. Alternatively, use the CPU's built-in Web Server: navigate to http://<cpu-ip>/ and check Module Information > Identification > Firmware.

Firmware Version Notes

Common firmware releases for the 1212C and their characteristics:

Always download the firmware matching your exact MLFB. Mixing V2.x firmware on a CPU with a newer hardware revision may not be supported and can result in the bootloader rejecting the image.

Troubleshooting Matrix

Alternative Workarounds When a SIMATIC MC Is Unavailable

The SIMATIC MC 24 MB is the only supported path for a field firmware update. When one cannot be obtained quickly, evaluate the following options in priority order:

1. Borrow from local Siemens support or distributor — the card is reusable and the firmware file is rewritten for each update.
2. Replacement CPU — a new 1212C ships with the latest firmware and may be more cost-effective than purchasing the card separately.
3. TIA Portal online firmware update — using TIA Portal V13 SP1+ on a connected engineering station, the firmware can be pushed over Ethernet via Online & Diagnostics > Firmware Update. This requires TIA Portal, a working Ethernet connection, and a CPU already responsive on the network. The same SIMATIC MC is not required for this path, but the CPU must be online and STOP.

Safety and Handling

• Observe ESD precautions when handling the SIMATIC MC.
• Do not insert or remove the card while the CPU is in RUN unless documented as a hot-swap operation for the specific firmware version.
• Store the card in its original ESD packaging when not in use.
• Never write to the card on a non-Windows system that may re-apply journaling (for example, macOS Finder's hidden .DS_Store files have been reported to interfere with older card images).

FAQ