Siemens LOGO! FBD Layout Loss After Upload: Reference Guide

Siemens LOGO! FBD Layout Loss After Upload: File Format Architecture and Recovery

The Siemens LOGO! is a modular logic module (smart relay) programmed in LOGO!Soft Comfort. The graphical Function Block Diagram (FBD) workspace places blocks on a 2D canvas using x/y coordinates. When a project is uploaded from a LOGO! device to the PC, the visual layout is frequently scrambled, blocks overlap, lines cross, and the original arrangement is lost. This article explains the underlying file format architecture, why the layout is not retained, and how to recover or protect the original appearance.

The companion LOGO! 8 System Manual (109751041) and the LOGO!Soft Comfort V8.4 documentation (109973006) are the primary engineering references for the topics covered here.

1. Problem Statement and Symptoms

When uploading a program from a LOGO! device or opening a file exported from the device, the engineer observes:

• FBD blocks appear clustered in the upper-left corner of the workspace.
• Blocks are stacked vertically regardless of the original spread layout.
• Connection lines cross each other and pass behind blocks.
• Comments attached to specific blocks appear on unrelated blocks.
• Block numbering (B001, B002, ...) is preserved but spatial relationships are lost.
• Workspace zoom defaults to "fit to window" rather than the original ratio.

The program logic itself remains intact. Inputs, outputs, timers, counters, analog blocks, and network references execute identically. What is lost is purely the visual presentation: the x/y coordinate of every block, the routing path of connectors, the canvas zoom factor, and the grouping of sub-circuits into pages.

2. LOGO! File Format Architecture

LOGO!Soft Comfort distinguishes between project files that live on the engineering PC and the program image that lives inside the LOGO! module. They are not the same file type, and they do not contain the same data.

The .lsc file is the only format that carries the visual FBD layout. Every other format is a logic-only image.

Internal Structure of the .lsc File

A .lsc file is a ZIP archive. The internal structure (for LOGO!Soft Comfort V8.3 / V8.4) typically contains:

• project.xml — main project data and metadata
• circuit/ — FBD diagram subdirectories
• circuit/*.xml — individual page diagrams with block coordinates
• resources/ — icons and symbol graphics
• Author, version, and device target metadata

A circuit page XML file (simplified excerpt) carries block coordinates:

<fbd>
  <block id="B001" type="AND" x="120" y="80" comment="Start enable"/>
  <block id="B002" type="OR"  x="320" y="80"/>
  <block id="B003" type="TON" x="520" y="80" param="PT=5s"/>
  <wire from="B001.out" to="B002.in1"/>
  <wire from="B002.out" to="B003.in"/>
</fbd>

The x and y attributes are the canvas coordinates. These exist only in the .lsc archive; they are stripped before the program is written to the LOGO! device. Therefore, the round-trip PC → LOGO! → PC loses every coordinate.

3. Why FBD Layout is Lost on Upload

The LOGO! firmware (LOGO! 8.x, 6ED1052 series, e.g. 6ED1052-1MD08-0BA2) stores the user program as a compiled token list in non-volatile memory. The compiled image contains:

• Block function codes
• Block instance parameters (timing, thresholds, presets)
• Input and output signal references
• Comment text strings
• Page/section boundaries (limited)
• Password protection state

The firmware does not store:

• Pixel coordinates of blocks on the FBD canvas
• Connector waypoint routing
• Canvas zoom level
• Block color or icon orientation
• Sub-page grouping
• Free-form annotation graphics
• User-assigned block names (alias) — only the auto-generated B-numbers

When LOGO!Soft Comfort issues "PC ← LOGO!" (upload), it receives the .lma archive from the device and opens it in the editor. The editor has only the compiled token list, so it must regenerate the visual diagram. The regeneration algorithm places blocks in a top-to-bottom flow, starting at coordinate (0, 0), with no memory of the user's original arrangement.

The same is true for .bin, .lld, and any direct download-to-logic-module flow where the source is the device rather than a project file. The exception is the .lsc file itself, which is the native project format and contains layout.

Round-Trip Data Flow

1. Engineer edits in LOGO!Soft Comfort on PC.
2. The .lsc file holds layout + logic on the PC.
3. PC → LOGO! (download): LOGO!Soft Comfort strips layout, compiles to token list, writes to device EEPROM.
4. LOGO! runs the program in firmware.
5. LOGO! → PC (upload): device returns compiled token list only.
6. LOGO!Soft Comfort reconstructs FBD from tokens with default layout.

Net result: a full round-trip from PC to LOGO! and back loses the layout. Layout is preserved only when the .lsc file stays on the PC and is used as the working master.

4. LAD vs FBD View Behavior

LOGO!Soft Comfort offers two editors: FBD (default) and LAD (Ladder Diagram). They behave differently on upload.

If layout fidelity after upload is the priority, ladder view appears unaffected because it auto-routes from the rung list. The appearance is "preserved" only because the editor regenerates the same ladder every time. This is regeneration that happens to be deterministic, not true preservation.

5. Preserving Layout: Step-by-Step Procedure

The following procedure protects the visual FBD layout through the project lifecycle.

1. Treat the .lsc file as the canonical master. Store it in version control (Git, SVN, or a managed PLM/automation repository) with check-in comments for every change.
2. Never distribute the .lma file as a working document. The .lma is for firmware-level backup, not for engineering collaboration.
3. After any upload from a device, immediately do "File → Save As" to create a new .lsc project. Document the upload event in the revision history.
4. Open the uploaded .lsc and use "Tools → Auto Format" (or "Arrange → Auto Arrange", depending on the LOGO!Soft Comfort version) to re-flow the FBD. This is not the original layout but it is a clean, readable approximation.
5. Use "File → Export → Diagram as Image" to capture the original layout as PNG before any device round-trip. Store the image alongside the .lsc in the version-controlled folder.
6. Configure "Tools → Options → Diagram" to enable grid snap and to show block reference numbers. This makes manual re-arrangement faster when only small shifts are needed.
7. Use meaningful block comments. They survive the round-trip and help identify blocks after the layout is lost.
8. Apply password protection on the LOGO! device only when needed. Passwords protect against unauthorized upload but do not affect layout preservation.
9. For multi-page programs, set page boundaries explicitly with "Edit → Page Properties" so the FBD has stable sub-circuits that can be re-arranged page by page.
10. Before downloading to the LOGO! for the first time on a new project, export the diagram to PDF and attach it to the project documentation.

6. Auto-Format and Manual Layout Tools

LOGO!Soft Comfort provides several layout tools. The exact menu labels depend on the version.

For an uploaded program, the most effective recovery sequence is:

1. Tools → Auto Format
2. View → Zoom → Fit to Window
3. Manual fine-tune on the most important sub-circuits
4. File → Save As (new revision)

The "fit to window" zoom setting is the default. If the engineer prefers a 100% or 150% default, change it under "Tools → Options → Diagram" before saving the master .lsc.

7. Block Comments and Reference Numbers

Comments and reference numbers are the most reliable identifiers across a round-trip. Use them heavily.

• Reference number (B001, B002, ...) is assigned by the editor and is stable. It is preserved through upload and download.
• Comment text is stored as a string in the project and on the device. It survives upload.
• Block name (user-assigned alias) is stored only in the .lsc and is not on the device. It is lost on upload.

Best practice: keep names short and meaningful, and put detailed descriptions in the comment field. Example:

B001 - name=HEAT_EN,  comment="Permit from HMI + thermostat"
B002 - name=COOL_T,   comment="Off-delay 30 s after stop"
B003 - name=PUMP_IL,  comment="Inhibits pump if door open"

After an upload, the comments and B-numbers allow the engineer to identify each block and re-arrange them into the original logical flow.

8. Layout Survival Matrix and Version Notes

LOGO!Soft Comfort Version Differences

The .lsc project format has been backward-compatible since V8.0. Files from V8.0 can be opened in V8.4. Older LOGO!Soft Comfort (V6, V7) used .lsc.zip; these open in V8.x with a one-time format migration.

9. Verification Checklist

After any round-trip operation, verify the project integrity with the following checks.

1. Open the .lsc file in LOGO!Soft Comfort and confirm the program compiles without errors ("Tools → Compile" or F9).
2. Use "PC ← LOGO!" upload and compare the uploaded logic against the .lsc master by counting blocks and verifying reference numbers.
3. Verify that the LOGO! device firmware version matches the LOGO!Soft Comfort version (e.g., LOGO! 8.4 firmware on a V8.4 project). Mismatches can cause logic errors that are unrelated to layout.
4. Confirm that all block comments are present and readable on the device display (LOGO! devices show a limited set of comments on the onboard screen).
5. Trigger each input manually and verify the expected output in the LOGO!Soft Comfort simulation ("Tools → Simulation").
6. Check the password protection state on the device ("Tools → Options → Password") and confirm it matches the documentation.
7. Document the round-trip in the project revision log with date, source, target, and operator.

10. Common Pitfalls and Field Notes

Related Tools and Documentation Aids

• LOGO! Web Editor (LOGO! 8.3 and later with TDE display) — browser-based interface for monitoring only, does not edit layout.
• LOGO! Access Tool — exports the program variable list as CSV for PLC-to-PLC or HMI integration; does not preserve layout.
• LOGO! TDE (Text Display) external display — shows the program on a remote 6-line display; layout-independent.
• Custom documentation workflow — export the FBD as SVG from LOGO!Soft Comfort, embed the SVG in Confluence, Notion, or a wiki, and store the .lsc alongside.

11. Summary and Recovery Workflow

The FBD layout in a Siemens LOGO! project is stored only in the .lsc project file on the PC. The LOGO! device stores compiled program logic without coordinates. Any upload from the device, or any file derived from a device, will lose the visual layout. The layout can be preserved and recovered by:

• Keeping the .lsc as the canonical master
• Avoiding .lma as a working document
• Exporting PNG/PDF/SVG of the diagram for archival
• Using comments and reference numbers to support post-upload recovery
• Using the LAD view when visual preservation matters less than functional clarity
• Configuring grid snap, block numbers, and zoom in the master .lsc

For complex projects with hundreds of blocks, the .lsc master is the only reliable source of the original visual layout. Engineers should treat the .lsc as the single source of truth and treat device upload as a logic-only recovery operation that will not reproduce the original FBD appearance.