S7-1200 SIMATIC Transfer Card: Fixing Program Mode Lock

Engineers maintaining SIMATIC S7-1200 CPUs frequently encounter a situation where a SIMATIC Memory Card (SMC) previously loaded with a STEP 7 (TIA Portal) project continues to behave as a Program card even after the engineer deletes the project files, reformats the card, and attempts to re-provision it as a Transfer card. This article documents the operational difference between the two card types, the root cause of the most common conversion failure, and the exact Siemens-documented procedures to produce a working Transfer card on the S7-1200 platform.

Problem Details: S7-1200 Card Locked in Program Mode

From chapter 3.4 of the S7-1200 Programmable Controller System Manual, the SIMATIC memory card is a small storage medium used in the S7-1200 CPU. Once inserted, the card can serve in one of the following roles:

• Program card – the entire STEP 7 user program and runtime data are stored on the card; the CPU's internal load memory is overwritten by the card's contents and the internal load memory is erased. With the card inserted, the user program is executed from the card. If the card is removed, the CPU no longer has an executable program.
• Transfer card – the card contains a STEP 7 project (under a special directory layout) that is automatically copied into the CPU's internal load memory at the next power-on or power-cycle of the CPU. After the transfer completes, the project is fully usable even if the card is removed.
• Empty / firmware update card – the card contains a firmware update job that is applied at the next CPU restart.

The reported symptom: an engineer has an SMC that previously operated correctly as a Program card. After deleting the project files on the card via Windows Explorer (or fully reformatting the card to FAT16/FAT32), the engineer attempts to follow the manual's procedure to create a Transfer card. The card continues to behave as a Program card on the next CPU restart. Deleting or formatting the card on the laptop does not change the role detected by the S7-1200 CPU.

This behavior is not a fault in the S7-1200 firmware. The S7-1200 identifies the role of the card by the presence (or absence) of specific marker files written into the root directory of the card by the TIA Portal / STEP 7 download dialog (or by a CPU-inserted Program-to-Transfer procedure). If those files are not written correctly, the card simply defaults to whatever mode the previous card image implies, which on a previously-used Program card means Program mode again.

How SIMATIC SMC Card Modes Work

The S7-1200 CPU inspects the inserted card during the power-on sequence. Card evaluation is not continuous; the CPU only reads role information at OFF/ON transitions. Once a role has been set, the CPU persists the project in the role-appropriate memory (internal load memory for Transfer cards, card-resident for Program cards) and runs from that location.

The role decision is driven by marker files the TIA Portal or the CPU itself writes to the card root. Manually copying or deleting these files outside the TIA Portal / STEP 7 card-provisioning function is not a supported way to switch the card's role.

Root Cause: Card Reader Compatibility and File Layout

The single most common root cause of the "card stuck in Program mode" symptom is the card reader used to write the project to the SMC. In the case that motivated this article, the engineer was using a generic multi-slot USB card reader that accepted MMC, SD, and MS cards in one shared slot. With that reader, every write attempt produced an apparently normal file listing on the laptop, but the S7-1200 CPU still detected the card as a Program card. Replacing the multi-slot reader with a dedicated HAMA USB card reader with a separate MMC slot immediately resolved the issue.

The underlying mechanism is that the S7-1200 expects the SMC to be written with a specific directory layout and a specific set of marker files. The TIA Portal / STEP 7 card-writing functions rely on the host card reader presenting the card with attributes that match the SMC's expected geometry. Some multi-slot readers expose the card as a generic SD/MMC mass-storage device but do not correctly mirror every attribute the S7-1200 expects when the card is returned to the CPU slot. A dedicated MMC reader presents the card with the precise combination the CPU uses to decide which mode to apply.

Three other contributing causes appear repeatedly in field reports:

1. Card was not actually blank when written. The TIA Portal card-creation function checks the card before writing. If residual SIMATIC.S7S / FWUPDATE.S7S files are present (for example, from a prior Program card image that was copied rather than properly re-provisioned), the tool may preserve them and re-emit a Program card image. Manually deleting these files with Windows Explorer is not equivalent to re-provisioning the card with the TIA Portal "Transfer card" function.
2. Card was formatted to a non-supported file system. S7-1200 SMCs are typically pre-formatted to FAT16/FAT32. Reformatting on the laptop to exFAT or NTFS is not supported; the CPU will not read the card and may default to interpreting it as a Program card from prior internal state.
3. Card was not ejected cleanly. Removing the card from a USB reader before the write buffers were flushed leaves the marker files in a partial state. The next CPU power-up detects an incomplete Program card and behaves accordingly.

Required Hardware and File Layout

Method 1: Create Transfer Card via External Card Reader

The S7-1200 System Manual chapter 3.4 documents two paths to create a Transfer card. The first path uses a card reader attached to the engineering PC only.

1. Insert a blank SIMATIC memory card into the card reader attached to the PC. The card must be in its factory state or have been fully re-provisioned by the TIA Portal card function; manually deleting files is not a substitute.
2. In TIA Portal, open the project you want to deploy, then select the S7-1200 CPU and choose the card operation you want from the project tree. For a Transfer card, the typical entry is "SIMATIC Card Reader > Transfer" (or the equivalent menu in your STEP 7 version).
3. Select the target card drive that corresponds to the USB card reader. Confirm the file system is FAT16/FAT32. TIA Portal writes the project plus the SIMATIC.S7S marker so the CPU recognizes the card as a Transfer card on the next power-up.
4. Safely eject the card from the PC's card reader. Do not interrupt the write — partial writes leave the card in an undefined state.
5. Insert the card into the S7-1200 CPU's card slot with the CPU powered off.
6. Power-cycle the CPU (OFF, then ON). The CPU evaluates the card, copies the project into internal load memory, then runs from internal load memory. The Transfer card can be removed after the transfer completes.

Method 2: Create Transfer Card via S7-1200 CPU

The second documented path uses the S7-1200 CPU itself to populate the card, which avoids dependence on the host card reader for the initial write.

1. With the CPU in STOP, download the desired STEP 7 project to the CPU's internal load memory over PROFINET / Ethernet using TIA Portal.
2. Insert a blank SIMATIC memory card into the CPU's card slot while the CPU is powered. The CPU detects the card.
3. Use TIA Portal's "Project > Card Reader > Transfer" command (or the CPU's online card operations) to copy the internal project to the card as a Transfer card image. The CPU writes the required marker files directly to the card.
4. After the write completes, power-cycle the CPU. The CPU recognizes the card as a Transfer card, copies the project back to internal load memory, and runs from internal memory.

Method 2 is the recommended path when the engineer's PC-side card reader is suspect. Because the CPU itself writes the card, the role-detection files are guaranteed to be correct for that CPU's firmware generation. This method is also the safest way to recover a card that was previously mis-provisioned by an unreliable USB reader.

Step-by-Step Power-Cycle Evaluation Procedure

Per the Siemens S7-1200 System Manual and the Siemens support entry on transfer cards, the CPU evaluates a card only at power-on. Card role changes therefore require an OFF/ON transition of the CPU. The procedure:

1. CPU must be in STOP or power-off before the card is inserted or removed. Inserting or removing the card with the CPU in RUN can corrupt the project on internal load memory.
2. Power off the CPU (PS OFF, then PS ON) or use the TIA Portal "Reset to factory settings" / power-cycle sequence.
3. Observe the CPU's LEDs during power-up. The RUN/STOP, ERROR, and MAINT LEDs indicate the result of the card evaluation. A successful Transfer card load is followed by the CPU entering RUN with the loaded project.
4. If the CPU does not enter RUN, the card was not recognized as a Transfer card. Remove the card, re-create it using Method 1 or Method 2 above, and re-insert.
5. After the transfer completes, the card can be removed. The project should continue to run from internal load memory with the card absent.

Firmware and CPU Compatibility Constraints

Card version compatibility is a hard constraint on the S7-1200. The Siemens support entry for transfer cards explicitly warns:

• Do not insert V3.0 program / transfer cards into later-model CPUs.
• Insert the transfer card into the CPU.
• Power-cycle the CPU to evaluate the memory card.

Source: Siemens Industry Online Support – SIMATIC S7 S7-1200 Programmable controller (entry 109759862).

CPU firmware revisions affect which card versions the CPU will accept. If a card written for an older firmware revision is inserted into a CPU with newer firmware (or vice versa), the CPU may not accept the card or may default to Program-card behavior. Cross-check the card's version label against the CPU's firmware release notes on the Siemens support portal before assuming a card failure.

When the CPU firmware is upgraded, older SMCs may need to be re-provisioned with the new firmware-aware card layout. The TIA Portal download dialog will warn the engineer when the project is being written to a card that the current CPU firmware does not support, and the engineer should treat that warning as a hard stop until the card is re-created through Method 1 or Method 2 with a compatible TIA Portal version.

Verification: Confirming Transfer Mode Operation

After a Transfer card is inserted and the CPU power-cycles, verify that the transfer was successful:

1. Establish an online connection from TIA Portal to the CPU. The project loaded from the card should appear in the online view with matching name, version, and block checksums.
2. Compare the online block checksums against the offline project. Identical checksums confirm the card image was loaded without modification.
3. Remove the Transfer card with the CPU in STOP. If the project continues to run (RUN LED steady green, no SF / BF errors) after the next power-on, the transfer completed and the CPU is running from internal load memory. If the CPU goes to STOP when the card is removed, the card was still in Program mode and the project was running from the card itself.
4. Check the CPU's diagnostic buffer for the entry "Transfer of project from card completed" (or the equivalent message in the CPU's firmware language). A failure to transfer leaves a diagnostic entry pointing to card read errors or invalid marker files.
5. Use the TIA Portal online "Online & diagnostics" view to confirm the CPU's current project source. The view should report the project as resident in internal load memory, not on card.

Diagnostic Buffer and LED Behavior

The S7-1200 CPU records every card evaluation in its diagnostic buffer. The relevant entries are:

LED patterns to observe during card evaluation: a brief MAINT blink during power-up is normal as the CPU reads the card. A solid ERROR (red) or a RUN/STOP blink pattern that does not settle to RUN indicates the card was rejected. Capture the diagnostic buffer immediately after a failed power-up to preserve the relevant event entries.

Field-Proven Best Practices

1. Always use a Siemens-branded SMC. Third-party SD cards are not supported and frequently fail to be recognized consistently across CPU firmware revisions.
2. Use a card reader with a dedicated MMC slot. Multi-slot MMC/SD/MS readers are the most common source of "card stuck in Program mode" complaints. The HAMA USB card reader with a separate MMC slot is a field-verified example that works reliably.
3. Always eject the card through Windows' "Safely Remove Hardware" before removing it from the reader. Removing the card during a buffered write leaves the marker files in a partial state and forces re-provisioning.
4. Always power-cycle the CPU to evaluate a new card. Hot-insertion is not supported for role changes. The CPU evaluates the card only at OFF/ON.
5. Use Method 2 (CPU-driven provisioning) when the host card reader is suspect. The CPU writes the marker files directly, eliminating card-reader compatibility as a variable.
6. Re-provision — do not reformat — when switching roles. Manual file deletion or Windows reformatting does not produce a valid Transfer card image. The TIA Portal / STEP 7 card-provisioning function must be used.
7. Label the card with its role and version. Field service personnel frequently mis-deploy Program cards as Transfer cards (or vice versa) because the cards are physically identical. A label on the card reduces deployment errors.
8. Keep a known-good Transfer card for emergency recovery. If the active project is corrupted, a verified Transfer card allows the engineer to restore the project on the next CPU power-up without needing a PC at the machine.

Troubleshooting Matrix

Frequently Asked Questions