LOGO!SoftComfort Upload: Recovering Comments and Rung Sequence

1. Problem Overview

When an engineer designs a circuit diagram in LOGO!SoftComfort using the Ladder Editor, attaches comments to inputs, outputs, and timers, and arranges the rung sequence so that Q1 is the first line, Q2 is the second, and so on, those human-readable artifacts are saved only inside the LOGO!SoftComfort project (.lsc) file on the PC. The transfer to the LOGO! device stores only the executable logic. When the program is later uploaded from the LOGO! back to LOGO!SoftComfort, three observable symptoms appear:

• The program name is replaced by the default Circuit Diagram1.
• All editor comments disappear from inputs, outputs, and function blocks.
• The rung order is reshuffled by the LOGO!SoftComfort import logic — Q7 can become the first line instead of Q1.

These symptoms have been confirmed on a LOGO! 230RCO with catalog number 6ED1 052-2FB00-0BA6 running LOGO!SoftComfort Ladder projects, and the behavior is by design rather than a fault. Understanding the underlying memory layout is the key to preserving engineering content across round-trips.

2. LOGO! Memory Architecture: What Is Stored Where

The LOGO! Basic module family separates its non-volatile memory into two physically and logically distinct regions. Only one of them reaches the controller over the programming cable; the other lives entirely inside the PC-side project archive.

2.1 On-device program memory

The LOGO! stores the compiled circuit diagram. This region holds the boolean expression list, timer and counter preset values, block interconnections, and the block names that the engineer typed into each function block. It does not hold:

• Free-form text comments placed in the Ladder editor.
• I/O tag comments (e.g., descriptions on I1, I2, Q1).
• The graphical layout — block positions, line routing, page assignments.
• The project file name or author metadata.

2.2 Layout memory (graphical information)

For documentation purposes, the LOGO! allocates a fixed layout memory for the graphical arrangement of function blocks and connecting lines. Per Siemens support FAQ 109478376, this budget is approximately 30,000 bytes on the LOGO! 6 series. The layout memory stores geometry only; it does not include editor comments, project names, or Ladder/FBD/UDF editor style decisions.

3. Round-Trip Behavior: What Survives a Transfer

A clean round-trip — PC → LOGO! → PC — returns only the subset of the original project that was ever stored on the device. The following table summarizes what survives, what is lost, and what is reconstructed.

4. Root Cause Analysis

Three independent factors combine to produce the observed symptoms:

4.1 Memory budget constraint

The LOGO! 230RCO (6ED1 052-2FB00-0BA6) belongs to the LOGO! 6 series, which uses a microcontroller-class non-volatile memory architecture. The full layout memory budget is documented at 30,000 bytes in Siemens support FAQ 109478376. This figure must absorb block coordinates, wire geometry, page structure, and block name strings. Adding free-form editor comments — which can be unbounded in length — would either exhaust this budget on modest programs or force a hard cap that breaks engineer workflow. Siemens chose to exclude comments from the device entirely.

4.2 No semantic distinction between "logic" and "documentation"

The Ladder editor stores comments and the rung layout as parallel metadata streams attached to the compiled logic. When the LOGO! receives the program, it stores the logic and a stripped layout. There is no on-device representation of editor comment text, so an upload cannot reconstruct what was never written. There is also no checksum or hash of the comment text included in the on-device image, so the upload cannot even detect that comments were present in the original .lsc.

4.3 LOGO!SoftComfort re-layout algorithm

On upload, LOGO!SoftComfort parses the compiled logic and rebuilds a fresh Ladder diagram using its own block placement algorithm. The algorithm optimizes for readability of signal flow rather than preservation of the original rung order. Outputs that share a common input chain are typically grouped, which is why Q7 can become the first rung even though it was originally the seventh. The default program name "Circuit Diagram1" is hard-coded into LOGO!SoftComfort as the placeholder for projects lacking stored metadata. The placeholder string is defined in the LOGO!SoftComfort resource files and can be inspected by extracting the executable with a ZIP tool — useful for forensic work.

5. LOGO! 6 Series Hardware Reference

The 230RCO variant cited in the source is part of the LOGO! 6 generation. Key specifications relevant to this issue:

The "6ED1 052-2xx00-0BA6" catalog number scheme (digits 9–12 of the part number) identifies the LOGO! 6 family. LOGO! 8 modules use the 6ED1052-xMD08-0BA0 scheme. The "-0BA6" suffix on LOGO! 6 designates the variant released in the sixth revision of the LOGO! 6 series. Earlier "-0BA5" or "-0BA4" revisions have identical memory architecture but may carry earlier firmware.

6. LOGO! 8 Series: What Changed

The LOGO! 8 generation (firmware V8.0 and later, LOGO!SoftComfort V8.0 and later) increased the program memory to 400 function blocks and introduced the integrated web server, SD card support, and Ethernet connectivity. Documentation handling, however, follows the same principle as LOGO! 6:

• Block names still transfer to the device and are read back on upload.
• Free-form Ladder editor comments still do not transfer to the device.
• Project name and rung order are still reconstructed by LOGO!SoftComfort on upload.
• The 30,000-byte layout memory budget is preserved in LOGO! 8 for backwards compatibility, although the larger program memory allows more blocks within the same layout footprint.

Engineers familiar with Siemens S7-1200 or S7-1500 documentation transfer should not expect the same behavior on LOGO!. The LOGO! line predates the TIA Portal comment/UDT transfer model and has its own simpler data model. TIA Portal stores comments inside the PLC's symbolic address table; LOGO! has no equivalent symbolic table on the device.

7. Procedure: Preserving Comments Across Round-Trips

The only durable mechanism to preserve Ladder editor comments, project names, and the original rung sequence is to keep the LOGO!SoftComfort .lsc project file on the PC and to load from file whenever the controller is re-flashed. The PC → LOGO! → PC round-trip should not be used as a backup strategy. Follow this procedure:

1. Establish a project folder structure. On the engineering workstation, create a folder hierarchy of the form \\engineering-server\projects\SITE\AREA\LOGO!\. Use one subfolder per physical LOGO! device, named with the device's serial number or asset tag.
2. Save the .lsc file as the working master. In LOGO!SoftComfort, use File → Save As and overwrite the master file after every meaningful edit. The .lsc file is a ZIP archive that contains the logic, layout, comments, and project metadata.
3. Use Load from PC (Download). When commissioning, always transfer PC → LOGO! using Tools → Transfer → Load to Device. The device will receive the compiled logic plus block names but will discard editor comments.
4. Avoid Upload as a backup. Never rely on Upload from Device to retrieve the project. The uploaded copy will lack comments, project name, and the original rung order. Use the on-device program as a logic source for cloning to a replacement device only, then re-apply the documentation by opening the master .lsc.
5. Document block names for field serviceability. Because block names survive the round-trip and are visible on the LOGO! on-device display (where fitted), populate them deliberately with text that helps an on-site technician identify parameters. Example: MOTOR1_DLY, PUMP3_RETENT, FAULT_LATCH. Keep each name under 12 characters to avoid truncation on LOGO! 6.
6. Version the .lsc file. Embed the firmware version of LOGO!SoftComfort and the LOGO! device into the project notes. Use a naming convention such as PUMP_BAY_3_v17.LSC where v17 is the engineering revision. The LOGO!SoftComfort internal version string lives in Tools → Options → General.
7. Use source control where practical. For multi-engineer sites, commit the .lsc file to a version control system (Git, Subversion) with binary support enabled. Add an ASCII release note alongside each commit describing functional changes, since most diff tools cannot compare .lsc contents directly.

8. Working With .lsc Project Files

The LOGO!SoftComfort .lsc file is a compressed archive. Engineers performing forensic work on a corrupted project or comparing two revisions can extract the contents using any ZIP utility. The internal layout follows a stable schema across LOGO!SoftComfort V7.x and V8.x.

If a project is corrupted, rename project.lsc to project.zip, extract the contents, inspect each XML entry for well-formedness, and re-zip with the original archive structure. A common cause of "Circuit Diagram1" appearing after a clean download is a corrupted or missing project.xml entry inside the .lsc archive. The file must remain UTF-8 encoded; engineers using regional Windows code pages sometimes corrupt the XML headers when round-tripping through older backup tools.

9. Block Naming Best Practices

Because block names are the only documentation that survives a round-trip, treat them as the primary operator-facing interface. Apply these conventions:

• Length: Stay under 12 characters for LOGO! 6 compatibility; LOGO! 8 allows more but the on-device display truncates for the system menu.
• Case: Use UPPER_SNAKE_CASE to maximize readability on the LOGO! 6 / LOGO! 8 integrated display.
• Noun-first structure: Begin with the asset tag (e.g., P3 for Pump 3), then the function (e.g., RUN, FLT, DLY). Example: P3_RUN_DLY.
• Avoid special characters. The LOGO! on-device menu accepts only ASCII alphanumerics and underscore. Avoid spaces, slashes, and accented characters.
• Match the comment. When the .lsc file is opened on the PC, mirror the block name as a comment prefix so the engineer can correlate the on-device text with the in-editor documentation. Example block name P3_RUN_DLY pairs with the comment P3_RUN_DLY: Pump 3 run delay, 30 s preset.
• Unique across the project. Block names must be unique within a single circuit diagram. Duplicates are flagged by LOGO!SoftComfort on download and produce inconsistent behavior on the on-device menu.

10. LOGO!SoftComfort Version Notes

LOGO!SoftComfort V8.x is the current released line for LOGO! 8 hardware. V7.x supports LOGO! 6. Engineers upgrading from LOGO! 6 to LOGO! 8 should perform the migration using LOGO!SoftComfort V8.x's Tools → Convert function, which preserves the .lsc structure including comments. The converter re-emits the block layout but keeps the original block names. Confirm successful conversion by inspecting the converted .lsc in the editor — comments, project name, and rung order from the LOGO! 6 source should appear unchanged in the LOGO! 8 destination.

11. Diagnostic Checklist

Use this matrix to triage unexpected upload behavior:

12. Verification Steps After Recovery

1. Open the master .lsc file in LOGO!SoftComfort and confirm the project name, comments, and rung order appear as designed.
2. Use Tools → Simulation to validate the logic against the original functional specification. Verify timer presets match the documented values.
3. Re-download to the LOGO! device with Tools → Transfer → Load to Device. Confirm the device accepts the program and enters RUN mode without error.
4. On the LOGO! device (or via the LOGO! 8 web server for V8.x), navigate the on-device menu and confirm the block names display as expected. Validate that names are not truncated.
5. Test the operational sequence on the physical I/O. Pay particular attention to timer and counter presets, which sometimes drift if the wrong .lsc was transferred.
6. Confirm the LOGO! is in RUN and not STOP. If the device powers up in STOP, check for program errors reported via the integrated display or web server.
7. Commit the recovered .lsc to source control with a release note describing the recovery action.

13. Layout Memory Budget: When 30,000 Bytes Is Not Enough

Engineers pushing the LOGO! to its functional limits sometimes encounter a related symptom: the LOGO!SoftComfort download completes without error, but on upload the layout looks "squashed" with overlapping blocks and broken wire geometry. This is the layout memory budget exhaustion.

Symptoms include:

• Block coordinates clustered in a small region of the editor.
• Connecting lines drawn as straight diagonals instead of orthogonal routes.
• Page breaks inserted at unexpected locations.
• LOGO!SoftComfort warning dialog "Layout memory exceeded" during download.

Mitigations, in order of preference:

1. Reduce the number of distinct function blocks by consolidating logic into arithmetic or analog blocks.
2. Replace long block names with shorter codes; each saved character frees layout memory.
3. Split the project across two LOGO! devices communicating via Ethernet (LOGO! 8) or hardwired I/O.
4. Migrate to a Siemens S7-1200 if the LOGO! memory budget is fundamentally inadequate for the application.

The formula for the practical layout cost of a block is approximately:

where NameLength is the block name character count and ConnectionCount is the number of input/output terminals wired on the block. Use this as a sanity check when the budget approaches the 30,000-byte ceiling.

14. On-Device Serviceability: Reading Block Names Without a PC

For service technicians without a PC, the LOGO! on-device menu (on "L" variants such as the 6ED1 052-2HB00-0BA6) provides direct access to block parameters via the system menus. Block names guide the technician to the correct parameter. To access block parameters on the LOGO! 6:

1. Press ESC until the main menu appears.
2. Select Start to enter the program display.
3. Use the cursor keys to highlight a block; its name appears at the bottom of the screen.
4. Press OK to open the parameter menu (password protected on protected LOGO! variants).

For LOGO! 8 modules, the integrated web server exposes the same block names through the device's web interface at http://<logo-ip>/. Block names appear in the variable list and can be edited live with operator authorization. The web server is enabled by default on firmware V8.0 and later; disable it via the LOGO! configuration menu if network exposure is undesirable.