Resolving OP77B Unsupported Storage Card Error via Correct MMC

Problem Overview

The SIMATIC HMI OP 77B operator panel reports an "Unsupported storage card" message at boot when a Siemens Micro Memory Card (MMC) 6ES7 953-8LG30-0AA0 is inserted in its card slot. The same card, however, works correctly in an S7-300 CPU because the firmware image written to it at the factory is the S7-300 system image, not the HMI runtime image. The OP 77B validates the card content against its own runtime signature and refuses to mount a foreign image, which is exactly the protection the panel's firmware is designed to enforce.

Symptom stack observed in the field:

• Boot message: "Unsupported storage card — insert storage card and try again".
• Restore attempt via USB stick fails with the same wording.
• Serial restore over RS232 fails because the USB-to-serial converter used is not one of the small set of converters the OP 77B accepts.
• An MPI/DP OS update starts from TIA Portal but is aborted mid-transfer; on reboot, only RS232 and USB appear under Transfer Settings; MPI/DP is no longer listed.
• Device version reported: V07.02.03.00_01.55 (WinCC Flexible 2008 SP5 image family).

Root Cause Analysis

The OP 77B is a member of the SIMATIC 77 series and shares the storage interface with the TP 177B and OP 177B. According to the SIMATIC HMI OP 77B device manual, the panel is rated Protection Class I per EN 61131-2 and EN 50178, and its card slot accepts only MMC/SD media that carry the HMI runtime image (or the HMI option bitmap). A S7-300 MMC 6ES7 953-8LG30-0AA0 ships with the S7-300 firmware image; the OP 77B boot loader reads the first sector, fails the signature check, and returns the "Unsupported storage card" alarm without writing any data to the panel.

Why the USB restore path also fails: the OP 77B uses the USB port strictly as a backup/restore channel once the panel is running. If the project on the panel has been wiped or was never loaded, the panel's transfer settings are read from flash. A bad transfer setting (set to USB-only or with no valid source) blocks the USB restore from completing.

Why MPI/DP disappears after a failed OS update: when the OS image is partially overwritten, the device boots into a fallback image that exposes only the guaranteed-working channels — RS232 and USB. MPI/DP is re-enabled only when a complete OS image is written to the panel's internal flash and the transfer channel list is regenerated.

Correct Memory Card Selection

The MMC card family for SIMATIC products is shared across CPUs and panels but the firmware pre-loaded on each card is product-specific. The cross-reference for the OP 77B family is published by Siemens in the entry HMI Panels / Slots — which card fits which panel? (Siemens Support entry ID 21847868).

Two card roles exist in the OP 77B:

1. Option-bitmap card — a Siemens-supplied card with the HMI image used for a clean OS restore or feature enable. Order as 6GK7 953-8LP00-0AA0 (or current equivalent).
2. Backup/restore card — a standard SD/MMC formatted FAT16 or FAT32 used by Backup/Restore from the Control Panel to write or read a .psb (panel backup) file.

Preconditions Before Any Restore

Verify each of the following before attempting a transfer. The OP 77B is unforgiving about partial state and will lock the active channel after a failed transfer.

• Power supply: 24 V DC (±20 %), protected with the SELV/PELV insulation required by EN 61131-2.
• OP 77B firmware target: V07.02.03.00_01.55 (or the version stamped on the rating plate of your unit).
• Configuration tool: TIA Portal V13 SP2 or later for a project transfer, or WinCC Flexible 2008 SP5 for legacy project compatibility.
• One known-good RS232 path (zero-modem cable) and, separately, one USB stick of ≤ 4 GB formatted FAT16/FAT32.
• The correct HMI image card available on the bench.

Restore Path A — RS232 Zero-Modem Cable

The OP 77B IF1B port is an RS232 port configured as DCE. The standard serial transfer requires a null-modem (cross-over) cable, DB9 female to DB9 female, with the following pinout:

The default OP 77B transfer baud rate is 115 200 bit/s, 8 data bits, no parity, 1 stop bit, software flow control off. The DIP switches on the rear of the panel must be set so that DIP 1 (transfer enable) and DIP 4 (RS232 transfer mode) are ON, DIP 2 and DIP 3 OFF. Without this setting the panel will not respond to the PC's polling frame.

USB-to-serial converters: most off-the-shelf converters fail to enumerate on the OP 77B. Use either the Siemens PC Adapter USB (6ES7 972-0CB20-0XA0) on the MPI/DP port or, on the RS232 port, a converter based on the FTDI FT232 or Siemens-native chip set. Converters with the Prolific PL-2303 are known to mis-frame at 115 200 bit/s and should be avoided.

Procedure to start a serial restore from TIA Portal:

1. In TIA Portal, open the project and select Online → Extended Download to Device.
2. Set the PG/PC interface type to Serial (RS232), select the COM port of the USB-to-serial converter or the COM port of the Siemens Field PG, and set the baud rate to 115 200.
3. Hold the OP 77B in transfer mode: power up with the SD/MMC slot empty and DIP 1 in the ON position; the panel enters transfer mode automatically when no project is loaded.
4. Trigger the download. The panel first requests the OS image; allow TIA Portal to write the matching image (V07.02.03.00_01.55 or later). Do not interrupt power during this phase.
5. After the OS completes, TIA Portal pushes the project (compilation, then runtime). The panel restarts into the project.

Restore Path B — USB Stick

Once a project is loaded, the OP 77B exposes Backup / Restore in the Control Panel. The USB stick path requires that a valid project is already running. It is therefore a second-line restore path, used when the panel boots cleanly into WinCC Flexible runtime but the project needs to be replaced or rolled back.

1. Format the USB stick FAT16 (default on sticks ≤ 2 GB) or FAT32 (≤ 4 GB). No other file system is supported.
2. Pre-stage the backup file: <ProjectName>.psb placed in the stick's root directory.
3. On the panel, open Control Panel → Backup/Restore. Select Restore from USB.
4. Select the .psb file and confirm. The panel reboots after restore.

Restore Path C — SD/MMC Card Restore

The SD/MMC restore path is the only path that works when the panel is so corrupted that no project loads and no USB/serial path is open. The card must be a SIMATIC HMI option bitmap card or a card prepared with the correct image via ProSave on the engineering station.

1. Insert the prepared HMI image card into the powered-off panel.
2. Power up. The panel detects the card, validates the bitmap, and prompts Update operating system?
3. Confirm with the panel's tactile keys. The OS image is written to internal flash; the panel reboots.
4. After reboot, the panel is in transfer mode and accepts a project download over RS232, USB, or MPI/DP (if the OS supports the channel).

MPI/DP Recovery After an Aborted Transfer

An interrupted OS update resets the channel mask. The panel in the reported case showed only RS232 and USB after the failure. Recovery steps:

1. Confirm the panel boots and shows the runtime loader (no project).
2. Connect RS232 (zero-modem cable, 115 200 bit/s, DIP 1 + DIP 4 ON).
3. In TIA Portal or WinCC Flexible, perform a Reset to factory settings first: Online → Accessible Devices → OP 77B → right-click → Reset to Factory Settings. This clears the partial OS image and reverts the channel mask to defaults.
4. Then perform an OS update: Online → OS Update with the image matching the panel (V07.02.03.00_01.55 in the reported case).
5. Reboot. The Control Panel Transfer Settings menu should now show all three channels: MPI/DP, RS232, USB.
6. Reconnect MPI/DP at 1.5 Mbit/s (default) or 187.5 kbit/s for legacy MPI networks. Verify the panel address (default 1) does not collide with the S7 CPU address.

Firmware/OS Update Procedure

The OS update is the only operation that restores the MPI/DP subsystem when it has been wiped. Execute it from RS232 to keep the path deterministic:

1. Open TIA Portal, project view.
2. Select Online → Accessible Devices. If the panel does not appear, verify DIP 1 and DIP 4 are ON, the cable is a true null-modem cable, and the COM port is set to 115 200 bit/s.
3. Once accessible, right-click the panel and select OS Update.
4. Browse to the OS image file shipped with WinCC Flexible 2008 SP5 or the TIA Portal HSP for OP 77B (image family OP77B_V07.02.03.00_01.55).
5. Confirm. Do not power-cycle the panel during the OS write; the bar at the bottom indicates progress.
6. When the panel reboots, log in via the Control Panel and verify the version string matches the loaded image.

Project Transfer and Re-Provisioning

Once the OS image is intact, transfer the project:

1. In TIA Portal, compile the project for the OP 77B target. Check that the device version of the compiled project matches the panel's OS version; mismatches are the most common cause of an aborted transfer.
2. Select Online → Download to Device → Software (all).
3. Choose the channel in use (RS232 recommended for the first transfer after an OS update).
4. Confirm the overwrite prompt and wait for the project to load. The panel restarts into the new project.
5. Switch the active channel to MPI/DP if the production network is MPI: Control Panel → Transfer → Channel: MPI/DP → Address: 1 → Baud Rate: 1.5 Mbit/s.

Verification Checklist

• Panel boots without "Unsupported storage card" with the original S7-300 MMC removed.
• Correct SIMATIC HMI SD card inserted is accepted silently (no alarm).
• OS version string in Control Panel matches the loaded image (V07.02.03.00_01.55 or later).
• Transfer Settings lists MPI/DP, RS232, USB; all three can be selected and saved.
• Project loads and the first screen displays without error.
• A tag connected to the S7 CPU updates live (e.g., a clock tag updated by the CPU toggles every second).
• Backup to USB stick completes and the resulting .psb file size is non-zero and matches the project footprint.

Troubleshooting Matrix

Field-Proven Caveats

• Always pull the SD/MMC card before any RS232 transfer. A card left in the slot during a serial OS update can interrupt the write and brick the panel's channel mask.
• The OP 77B does not accept SDHC cards larger than 4 GB for backup/restore. For backup/restore, stay on FAT16/FAT32 sticks ≤ 4 GB.
• The Siemens Field PG's native RS232 port is the only guaranteed-good serial source for the OP 77B at 115 200 bit/s. USB-to-serial adapters are likely to fail the first poll.
• If the panel is part of a Profibus network, switch off Profibus traffic during the OS update. A noisy bus can interrupt the long write and produce the same "only RS232/USB" symptom.
• After restoring, re-check Transfer → Settings and disable any channel the production environment does not use (e.g., USB in a clean-room install).