Resolving LOGO! 0BA7 / 0BA8 SD Card Read Failure: Memory Card Selection Guide

When a Siemens LOGO! 0BA7 base module refuses to recognize an SD card inserted in its slot, the root cause is almost always card identity confusion at the part-number level. The 0BA7 and 0BA8 generations do not accept every card that physically fits the socket. The slot is keyed for the Siemens LOGO! Card (a pre-formatted, copy-protected SD card) and, on 0BA7, ordinary consumer SD cards formatted to FAT12, FAT16, or FAT32. A SIMATIC S7 MMC such as 6ES7953-8LP20-0AA0 is a completely different product line with a proprietary S7 file system and will never mount in a LOGO! base module. This reference details how to identify the wrong card, select the correct one, format it properly, and verify that the LOGO! 0BA7 or 0BA8 actually uses the media.

1. Problem Statement: SD Card Not Recognized

The reported failure mode is consistent across many field incidents:

• An SD card with Siemens part number 6ES7953-8LP20-0AA0 is inserted into the SD slot of a LOGO! 12/24RCE or LOGO! 230RCE (0BA7 generation).
• The base module does not mount the card; the SD activity LED does not blink, and LOGO!Soft Comfort V7.0+ reports that no card is present.
• Removing the card and reading it on a PC shows a non-FAT file system structure (proprietary S7 layout) that Windows cannot read without Siemens tooling.

The 0BA7 firmware does not include a fallback driver for the S7 MMC file system. The card is electrically compatible (same SD interface) but logically incompatible. The 0BA7 boot loader will silently ignore it.

1.1 Affected Hardware and Firmware

2. Root Cause: 6ES7953-8LP20-0AA0 Is Not a LOGO! Card

The 0BA7 manual is explicit: "LOGO! 0BA7 supports standard SD (Secure Digital) cards that support FAT12, FAT16, or FAT32 file system format." The 0BA7 cannot read or write the SIMATIC S7 MMC file system used on 6ES7953-8L... cards. The same limitation exists on 0BA8, but with a different physical format (microSD/microSDHC).

The reason a user typically ends up with the wrong part is procurement confusion. Both product lines use the same SD form factor on the S7-300 side and a near-identical visual appearance on the LOGO! Card side, but their MLFBs come from different catalog trees:

3. Correct Memory Card for LOGO! 0BA7

For the LOGO! 0BA7 (12/24RCE, 230RCE) the correct memory media are:

1. Siemens LOGO! Card 6ED1056-1DA00-0BA0 – a pre-formatted, copy-protected SD card sized for the LOGO! 0BA7. It uses the standard SD form factor and ships ready to plug in.
2. Any standard SD card formatted to FAT12, FAT16, or FAT32 – a commercial 1 GB / 2 GB SD card works for almost every 0BA7 program. SDHC (4 GB–32 GB) compatibility is firmware-dependent; ES02 firmware generally mounts FAT32 on consumer SDHC cards but the LOGO! Card remains the recommended media for long-term service.

The 0BA7 will use the card for three purposes:

• Circuit program storage – copy the .lsc program from PC/LOGO!Soft Comfort to the card, then transfer to another 0BA7 without a PC.
• Data log of process values – the base module writes CSV-style process data to the card when a Data Log function block is configured.
• Firmware update – when a valid LOGO! 0BA7 firmware .bin file is placed on the card, the module will flash itself on the next power-up.

4. File System and Capacity Requirements (0BA7)

5. LOGO! 0BA8 Memory Card: microSD / microSDHC

The LOGO! 0BA8 generation moved from the full-size SD slot to a microSD / microSDHC slot. The supported media list, derived from the 0BA8 manual excerpt and field reports, is:

The 0BA8 also accepts the Siemens-branded 6ED1056-1DA00-0BA8 LOGO! Card. This card is essentially a Siemens-labelled microSDHC that is pre-formatted and pre-licensed for copy-protected program transfer. It is the same physical media that any consumer 16 GB card uses; the added value is the Siemens warranty, the part traceability in a bill of materials, and a known-good blank state.

6. Program Memory and Circuit Program Size Limits

Independent of card size, the LOGO! 0BA7 and 0BA8 enforce a firmware-side limit on the circuit program that can be loaded into RAM from the card. Per Siemens Knowledge Base article "Memory space and circuit program size - LOGO!" (ID 109741041):

• Each circuit program is limited by the maximum number of function blocks allowed for that device generation.
• Each block consumes a fixed number of memory bytes in the program memory region.
• If the program exceeds the block count or the byte budget, LOGO!Soft Comfort will refuse the download and report the error in the status pane.

7. Step-by-Step: Replacing the Wrong Card with a LOGO! Card

7.1 Prerequisites

• One LOGO! 0BA7 (12/24RCE or 230RCE) with power removed, or a 0BA8 with the front flap open.
• One Siemens 6ED1056-1DA00-0BA0 LOGO! Card (0BA7) or 6ED1056-1DA00-0BA8 LOGO! Card (0BA8), or a known-good consumer SD / microSD card formatted to FAT12/16/32 (0BA7) or FAT32 (0BA8).
• PC with LOGO!Soft Comfort V7.0+ (0BA7) or V8.0+ (0BA8).
• Ethernet cable (for direct PC connection on 0BA7/0BA8 Ethernet SKUs).

7.2 Procedure

1. Power down the LOGO! base module. Do not hot-swap SD cards; the slot is mechanical-only and data corruption can occur if the card is removed while the Data Log block is writing.
2. Open the front cover of the base module to access the SD slot. On 0BA7 the slot is on the right side of the module under the door; on 0BA8 it is also under the door, but accepts a microSD.
3. Remove the incorrect 6ES7953-8LP20-0AA0 card and store it in the S7-300 / S7-400 spares bin. It belongs to a SIMATIC MMC, not a LOGO!.
4. Insert the LOGO! Card (or pre-formatted consumer SD) with the label side up until the spring latch clicks.
5. Reapply power to the LOGO!. The base module POSTs in < 5 s. The SD activity LED (where fitted) should pulse once if the card is recognized.
6. Connect LOGO!Soft Comfort to the LOGO! via Ethernet. In the menu bar, choose Tools > Transfer > LOGO! → PC to confirm the base module is online.
7. Copy the circuit program to the card:
   • Open the project in LOGO!Soft Comfort.
   • Select File > Memory Card > Copy LOGO! → Card.
   • Choose the target slot (the LOGO! Card is the default).
   • Confirm; the project is written to /LOGO/<projectname>.bin on the card.
8. Verify by removing the card, reading it on a PC with a USB card reader, and confirming the project file is present in the LOGO! directory.

8. Verification Checklist

Use this list to confirm the card is correctly installed and recognized:

9. Troubleshooting Matrix

10. Data Log Operation on a LOGO! Card

The 0BA7 and 0BA8 firmware support a configurable Data Log function block. When wired into a circuit, the block writes timestamped samples to a CSV file on the card. Practical settings:

After a Data Log session, eject the card and copy the CSV to a PC for analysis. A 1 GB LOGO! Card typically stores several years of 1-minute interval process data before rollover is required.

11. Sizing a Card for a Project

The 0BA7 program memory is device-resident, but the on-card file size depends on the project archive format:

For a circuit program of P bytes, the on-disk archive size is approximately:

card_file_bytes = P + 512 + 16 · N_blocks

where N_blocks is the number of function blocks in the program. The 512 bytes is the LOGO!Soft Comfort header and 16 · N_blocks is the per-block index.

For a typical 0BA7 program of 12 KB containing 80 blocks:

card_file_bytes = 12 288 + 512 + 16 · 80 = 14 080 bytes (≈ 14 KB)

A 1 GB LOGO! Card therefore holds tens of thousands of projects. The only practical storage limit is the FAT32 file-count ceiling of 65 535 entries per directory.

12. Network Communication Affects Card Behavior

On the 0BA7 (and 0BA8) Ethernet SKUs, the SD card operation is logically independent of the S7 communication stack, but both share the same SPI bus on early 0BA7 PCBs. Practical implications:

• Up to 8 S7 connections can be active simultaneously; card read/write latency may rise slightly under heavy S7 traffic.
• The 0BA7 supports only one Ethernet connection to a PC running LOGO!Soft Comfort at a time. A second PC attempting a connection will be refused until the first disconnects.
• Firmware update from the card is blocked while an S7 connection is open; the module waits for all S7 connections to close before flashing.

This is documented in the LOGO! 0BA7 system manual and is unchanged on 0BA8 with the exception that 0BA8 supports up to 8 S7 connections plus a LOGO!Soft Comfort connection in parallel.

13. Spare-Parts Strategy

For plants that mix LOGO! generations:

• Maintain at least two 6ED1056-1DA00-0BA0 LOGO! Cards per panel for 0BA7 spares.
• Maintain at least two 6ED1056-1DA00-0BA8 LOGO! Cards per panel for 0BA8 spares.
• Never co-mingle S7 MMCs in the same drawer; the label "SD card" is not enough to identify the part. Use the MLFB on the white sticker.
• For hazardous-area or vibration-prone cabinets, prefer the Siemens-branded LOGO! Card over consumer cards; the operating temperature range of the LOGO! Card is rated -20 °C to +70 °C.

14. Quick-Reference Card Matrix

15. Frequently Asked Questions