Resolving LOGO! 8 Ladder .lld Import Failure in Soft Comfort v8

Siemens LOGO! Soft Comfort V8.x restricts the import of *.lld (LAD) programs when the project is opened in Network Project Mode. Only *.lsc (FBD) programs can be imported or created. The default editor preference set under Tools → Options → General only governs the editing view; it does not override the import filter. This article documents the underlying constraint, the supported editor/file matrix, and the field-proven workaround that converts the LAD program to FBD, saves it as *.lsc, and then imports it into the target 0BA8 device node in the project tree.

Problem Summary

When working with a Siemens LOGO! 0BA8 (LOGO! 8) base module inside LOGO! Soft Comfort V8.x on Windows 7 Professional, an existing ladder diagram stored as *.lld cannot be imported directly. The Import dialog filters out *.lld files and only shows *.lsc. The user has already configured the default editor to Ladder under Tools → Options → General, yet the import behavior does not change because the option controls the editing view, not the file-type acceptance of the Import action.

Symptoms observed in the field:

• Import dialog lists only *.lsc files. The *.lld ladder program does not appear even when All files (*.*) is selected, and double-clicking the file opens a separate instance rather than importing.
• Right-click → Import on a 0BA8 device node is greyed out for *.lld source programs.
• Project tree shows a new device node for the 0BA8 but the circuit program slot remains empty after the attempted import.
• Setting the default editor to Ladder has no effect on import. The Tools → Options → General → Default editor setting governs only how a brand-new or freshly opened program is displayed in the diagram editor window.

Root Cause: Network Project Mode Import Restriction

LOGO! Soft Comfort V8.x supports two distinct top-level workspace modes:

1. Diagram Mode (single-program editor) — both LAD and FBD are first-class program representations. Users can create, open, save, and convert between them freely.
2. Network Project Mode (multi-device project tree) — the project tree may contain multiple LOGO! base modules and expansion nodes. Within this mode, only FBD-based programs (*.lsc) may be imported or newly authored. LAD is not a supported representation for imported or newly created circuit programs in this mode.

This restriction is enforced at the project-tree level and is independent of the user's editor preference. The internal circuit-program model used by the network project stores blocks in a format that mirrors the LOGO! 0BA8 firmware's FBD program representation. LAD files (*.lld) are essentially LAD-native serializations that do not map one-to-one onto this FBD-centric internal model without an explicit conversion step.

The conversion button labeled "Convert to FBD" in the diagram editor performs the necessary translation. Once executed, the program can be saved as *.lsc and subsequently imported into a network project device node.

LOGO! Soft Comfort v8 Editor Modes Compared

File Type and Editor Compatibility Matrix

Prerequisites

Before running the conversion workflow, confirm the following on the engineering workstation:

• LOGO! Soft Comfort V8.x installed. Versions V8.0, V8.1, V8.2, and V8.3 are all known to exhibit the same network-project LAD import restriction. Verify version via Help → About.
• Supported OS. Windows 7 Professional SP1, Windows 8.1, Windows 10 (1809+), or Windows 11. LOGO! Soft Comfort V8.0 was the last official build tested against Windows 7; V8.2 and V8.3 require Windows 10 or later.
• Source program on disk. The *.lld ladder program must be in a folder writable by the engineering user; the conversion step writes a new *.lsc to the same path by default.
• Project file location. The target *.lnp network project must be located on a local drive (not a network share) for reliable file-locking during import.
• User permissions. Write access to the project folder and the *.lld source folder.

Optional but recommended:

• A spare LOGO! 0BA8 on the bench, programmed via Ethernet for end-to-end verification (PC → switch → LOGO! 0BA8).
• Backup copy of the source *.lld file in a separate folder, since the "Convert to FBD" operation is non-destructive but the file may be resaved with format metadata changes.

Step-by-Step Conversion and Import Workflow

The end-to-end procedure is split into two phases: (A) Diagram-mode conversion of the LAD file to FBD, and (B) Network-project import of the resulting *.lsc.

Phase A — Convert .lld to .lsc in Diagram Mode

1. Launch LOGO! Soft Comfort V8.x and ensure the application opens in Diagram Mode. If the workspace currently shows a network project tree with multiple devices, close it (File → Close Project) so the application returns to the single-program editor.
2. Open the source *.lld file via File → Open or by dragging the file onto the workspace. The diagram editor renders the program in LAD view. Verify visually that all rungs loaded correctly before converting.
3. Convert to FBD. Click the toolbar button labeled "Convert to FBD". In V8.0 the icon is a two-block arrow (LAD → FBD). The dialog Do you want to convert the program from Ladder Diagram to Function Block Diagram? appears. Click Yes.
4. Inspect the converted program. Soft Comfort regenerates the circuit as FBD blocks. Confirm that:
   • All normally-open / normally-closed contacts are present.
   • All coils (Q outputs, memory flags M, jump labels) are connected.
   • Timers, counters, analog blocks, and any UDFs are present and parameterized.
   • No blocks show an exclamation mark indicating unresolved references.
5. Save as *.lsc. Use File → Save As and select LOGO! Program (*.lsc) as the file type. Pick a filename that clearly indicates the FBD variant, e.g. pump_seq_v3_FBD.lsc. Confirm the save.

Phase B — Import .lsc into the Network Project

1. Open or create the network project. In LOGO! Soft Comfort, choose File → New Project (or Open Project for an existing *.lnp). The workspace switches to Network Project Mode with a device tree on the left.
2. Add or select the target 0BA8 device node. Right-click the project root and choose Add Device → LOGO! 0BA8, or expand an existing device to expose its circuit program slot.
3. Import the FBD program. Right-click the target device's Circuit Program node and choose Import. The file-open dialog appears filtered to *.lsc. Navigate to the converted file and confirm.
4. Confirm the program appears in the device node's circuit program. The program is stored as FBD and is no longer convertible to LAD inside the network project.
5. Save the network project with File → Save (or Ctrl+S). Soft Comfort writes the updated *.lnp and associated *.lsc payloads.
6. Download to the LOGO! 0BA8. Right-click the device and choose Download → PC ↔ LOGO!. Confirm the Ethernet connection (or use USB cable) and complete the transfer.

Network Project Mode Import Walkthrough (Inline SVG)

The decision flow below summarizes the import path taken by Soft Comfort V8.x when a network project is open and a user attempts to load a program onto a 0BA8 device node.

Verification

After completing the import, verify that the program is functionally identical to the source *.lld by running the following checks in order.

1. Block-count parity. Compare the number of blocks in the original LAD (rungs × contacts/coils + blocks) against the FBD result. A discrepancy greater than 5% typically indicates a failed conversion of a UDF or an analog block.
2. Tag and address audit. Open Tools → Reference Data in the FBD program. Confirm that all I/O (I1–I24, Q1–Q16, AI1–AI8, AQ1–AQ2), flags (M1–M27), and shift-register bits (S1.1–S4.8) match the source LAD reference.
3. Simulation run. Use Tools → Simulation to start the LOGO! Soft Comfort simulator. Toggle each input used in the program and confirm the expected output, timer, or counter behavior. Soft Comfort's simulator uses the same runtime model as the 0BA8 firmware, so functional drift between modes is rare.
4. Online test against hardware. Connect the PC to the LOGO! 0BA8 via Ethernet and select Online → Start Online Test. Soft Comfort displays live I/O state. Manually exercise inputs and compare against the simulated results.
5. Download and cold-start. Perform a final download with PC → LOGO!. Power-cycle the 0BA8 to confirm the program is non-volatile and boots into RUN. The LOGO! display should show the configured text message and the green RUN LED should be steady.

Troubleshooting Matrix

Edge Cases and Caveats

UDF and Macro Preservation

User-Defined Functions (*.lma) and macros used inside the LAD source must be installed on the engineering PC before the conversion step. If a UDF is referenced by block name but not present in the local library, the converter may emit a placeholder block that lacks the macro's internal logic. Always re-install the UDF library set that accompanied the source program before converting.

Comment and Text-Message Loss

Inline rung comments in LAD are stored as block-property text in FBD. The conversion preserves comment strings but visually relocates them onto block properties dialogs. The "Show comment" toggle in the FBD view does not show legacy LAD-style inline notes. Use the Comment tab in the block's properties dialog to re-verify and reformat documentation after conversion.

Analog Threshold and Hysteresis

Analog comparator and threshold blocks retain their parameter set across conversion, but the gain/offset scaling constants are stored with full precision only when the target 0BA8 firmware is ES 02 or later. On early ES 01 firmware, the conversion may quantize the constants to the nearest displayable value. Verify analog behavior in simulation before relying on it.

Network Project Save Format

Network projects saved by Soft Comfort V8.x are not forward-compatible with LOGO!Soft Comfort V7. The internal *.lnp format changed. If a mixed-version team is involved, store the FBD *.lsc separately and re-create the network project on the older V7 workstation if a V8 import is not feasible.

Multiple 0BA8 Devices in One Project

When several 0BA8 nodes are present, each must hold its own FBD program. Importing the same *.lsc into multiple devices works, but the project file size grows linearly. For projects with more than four 0BA8 nodes, prefer splitting into separate network projects and linking via Ethernet routing rather than a single monolithic project.

Clock and Timer Block Parameter Rounding

On conversion, timer preset values are preserved exactly. The "Convert to FBD" path does not resample the time base. Edge cases where the original LAD file used non-standard 10 ms time bases (the legacy LOGO! 5/6 base) are remapped to the LOGO! 8 native 10 ms base. Verify any timing-critical ladder logic after conversion, especially where the legacy base was 100 ms or 1 s.

Field Notes and Best Practices

• Always keep a master *.lld. Treat the LAD file as the canonical, human-readable documentation of the control logic. The FBD *.lsc inside the network project is a derived artifact for runtime deployment.
• Name files semantically. Use suffixes like _LAD.lld and _FBD.lsc to keep variants unambiguous in version control and on shared drives.
• Set Tools → Options → General → Default editor to LAD for users who primarily author in LAD. Remember that this only affects newly created or standalone-opened programs — it does not enable LAD inside a network project.
• Validate in simulation first. Run the FBD program in the LOGO! Soft Comfort simulator with a representative input sequence before downloading to hardware. The simulator is cycle-accurate with the 0BA8 firmware and catches conversion drift quickly.
• Use Ethernet for download to 0BA8. USB download is supported but slower and locks the LOGO! display into a transfer mode. Ethernet keeps the HMI usable during PC ↔ LOGO! sync.
• Back up the network project before bulk import. Right-click the project root and choose Archive to produce a *.lna snapshot. This is the only way to roll back a corrupted *.lnp after an import failure.
• Document the conversion in the project log. A short note in the project README listing which devices were imported from which LAD master helps future maintenance engineers reverse the mapping if the original *.lld is updated.

Standards and Documentation References

The conversion behavior described above is consistent with the LOGO! 0BA8 system manual and the LOGO! Soft Comfort V8.x online help. Confirm firmware-specific limits against the official Siemens documentation before commissioning:

• LOGO! 0BA8 System Manual (Siemens Industry Online Support, entry ID 109751634)
• LOGO! Soft Comfort V8.0 Online Help and Function Manual
• Siemens LOGO! Product Family Overview
• Siemens Industry Online Support — LOGO! Downloads and Firmware