Fixing LOGO! 8.FS4 Online Monitoring After FS03 Program Import

Problem Overview

When migrating a LOGO! Soft Comfort (LSC) project from a LOGO! 8 with feature set 03 (0BA8 Standard, marketed as 8.FS3) to a LOGO! 8.FS4 to enable Modbus TCP communication, the program loads onto the new controller, executes correctly, and the controller runs as expected. However, LOGO! Soft Comfort Online Monitoring stops displaying the live state of inputs, outputs, flags (M markers), and analog variables. The status display freezes at the last connected state, shows dashes, or remains static while the controller clearly continues scanning the logic.

This symptom appears consistently across both Windows 7 and Windows 10 engineering stations and is independent of the Ethernet cable, switch, or IP address configuration. The root cause is a project-side device-type inconsistency that LSC does not validate during program import.

Affected Hardware and Software Versions

For official Siemens product information, see the Siemens LOGO! Software page and the Siemens Industry Online Support portal.

Root Cause Analysis

LOGO! Soft Comfort stores the target hardware description inside the LSC project file (the .lsc / .lscx archive) in two distinct places:

1. The Network Configuration (Tools → Ethernet Connections / Network view), which lists each LOGO! station, its IP address, subnet mask, gateway, and device class identifier.
2. The Device Properties of the LOGO! node itself, opened by double-clicking the LOGO! station in the project tree or right-clicking → Properties. This object holds the detailed hardware profile: 0BA8.Standard, 0BA8.FS4, 0BA8.FS5, 0BA8.FS6, expansion slot count, memory size, and the firmware revision expected by the project.

When you re-target an existing project to a newer LOGO! 8 generation, you typically open the network configuration, replace the device (e.g. select LOGO! 8.FS4 instead of LOGO! 8) and confirm the change. This action updates only the first record (network view). The second record (device properties) is left untouched because the dialog is separate and is not automatically refreshed by the network selection.

The result: the imported .lsc file still carries the FS03 device profile. The compiled code that the PC sends during the next PC → LOGO! download is built for the FS03 instruction set and FS03 register layout. The download succeeds because backward-compatible blocks are present, the program executes, and the FS04 controller is tolerant enough to run it. However, the Online Monitoring handshake uses the project-side hardware profile to negotiate the variable map. Because the project advertises an FS03, the FS04 controller cannot satisfy the monitoring request with its FS04 register layout, and the live state stream is silently dropped.

Solution: Align Device Type in Project Properties

The fix is to update the device-class identifier inside the LOGO! device properties of the LSC project. Once the profile matches the physical hardware, Online Monitoring re-negotiates successfully and live values return.

Prerequisites

• LOGO!Soft Comfort V8.1 or later installed on the engineering PC (V8.2 recommended; V9.0 fully supports FS04 → FS06 migration).
• The original .lsc / .lscx project file from the FS03 controller.
• Physical or VPN access to the FS04 controller's Ethernet interface.
• Current firmware for the target controller (see firmware update section below).

Step-by-Step Procedure

1. Open the project in LOGO!Soft Comfort. Launch the matching or newer LSC version. LSC V8.0 cannot fully edit FS04 projects — use V8.1 or higher. If the project opens with a banner indicating conversion, accept it; conversion is normal when migrating between feature sets.
2. Open Network Configuration. From the menu, choose Tools → Ethernet Connections (or Tools → Network Configuration depending on LSC version). Select the LOGO! station that you previously changed to FS04. Confirm that the device listed is LOGO! 8.FS4 (or FS05/FS06 if applicable) and that the IP address matches the physical controller.
3. Open the LOGO! Device Properties. In the project tree (left-hand panel, Network view or Devices and Networks), double-click the LOGO! station. The Properties dialog opens with several tabs (General, Ethernet, Security, System, etc.).
4. Update the Hardware Type. On the General tab, change the device / hardware type from 0BA8.Standard (FS03) to LOGO! 8.FS4 (or to FS05/FS06 if that is your physical hardware). Apply the change and confirm any prompt about program compatibility.
5. Verify the project compiles. Use File → Check Program Consistency or simply attempt a download. The compiler must succeed against the new device profile; warnings about newly available instructions or memory layout are normal.
6. Update the controller firmware. Before downloading, update the FS04 firmware to the latest released version (FS06 where supported) using the Siemens LOGO! Web Loader or the firmware update tool from Siemens Industry Online Support. Newer firmware resolves known monitoring bugs in early FS04 releases and unlocks full instruction coverage.
7. Re-establish PC → LOGO! connection. From the LSC menu choose Tools → Transfer → PC → LOGO! (or PC <-> LOGO!) and complete the download to the controller. Wait for the "Transfer successful" confirmation.
8. Start Online Monitoring. From the menu choose Tools → Online Monitoring (or click the Online Monitoring button on the toolbar). The status of inputs (I1…In), outputs (Q1…Qn), analog inputs (AI1…AI8), analog outputs (AQ1…AQ2), flags (M1…M27, M8…M25 byte flags), and Modbus holding registers should now update in real time.

Firmware Update Procedure (recommended)

1. Connect the PC directly to the LOGO! Ethernet port using a patch cable (or through a managed switch).
2. Browse to the LOGO! Web Server (default URL http://<logo-ip>) and log in with the user password.
3. Open the Module Information page and note the current firmware version (e.g. FS:04).
4. Download the latest LOGO! firmware LFA file from Siemens Industry Online Support (article ID 109751706 contains the current LOGO! 8 firmware bundle).
5. In the web server, navigate to Update Firmware, upload the LFA, and confirm the update.
6. The controller reboots with the new feature set. Re-attempt the download and online monitoring.

Verification

After completing the procedure, verify the fix using the following checks:

Why Feature Sets Matter for LOGO! 8

Siemens marks each successive revision of the LOGO! 8 base module with a Feature Set (FS) number. The feature set is a firmware-generation identifier, not a marketing label: it changes whenever the controller gains new instructions, new communication functions, new web pages, or a new memory layout. The active feature set is shown on the LOGO! display as FS:03, FS:04, FS:05, or FS:06 and on the web server module information page.

The original poster's scenario — needing Modbus TCP — is the most common reason to migrate from FS03 to FS04. Without FS04 (or higher) firmware, the LOGO! cannot expose a Modbus TCP server on its Ethernet port. This is independent of whether the FS03 program is logically correct.

Modbus TCP on LOGO! 8.FS4 — Quick Reference

After the migration succeeds and Modbus TCP is active, the following register map is exposed by the LOGO! 8.FS4 server on TCP port 502:

Reference the LOGO! 8 system manual for the exact register layout and unit IDs. The most recent manuals are available on the Siemens Industry Online Support portal under product "LOGO! 8" → Manuals.

Common Pitfalls During LOGO! Program Migration

1. Forgetting the Device Properties Profile

The single most common migration error, as documented in this case. Always open the Device Properties dialog after any network-level change.

2. Mismatched LSC and Controller Firmware

Pairing LSC V8.0 with an FS04 controller — or LSC V9.0 with an FS03 controller — produces inconsistent compilation. The recommended pairing rule is: LSC version ≥ feature set. Use LSC V8.2 or higher for FS04 devices.

3. IP Address Change After Restore Factory Settings

If the controller was factory-reset, its IP returns to 192.168.0.10. Update the LSC project's network configuration accordingly or use the LOGO! Web Loader to discover the device on the network.

4. Online Monitoring on Multiple PCs

LSC permits only one Online Monitoring session per controller. If a second engineering station opens Online, the first session is silently disconnected and may show frozen values.

5. Modbus TCP Holding Register Offset Confusion

Modbus uses 1-based addressing, while LOGO! variable IDs are 0-based internally. Some client tools (modpoll, pymodbus) require the offset to be applied manually; some apply it automatically. Confirm with a simple read holding register 401 test.

6. SD Card Program Transfer vs. Online Monitoring

Transferring a program via SD card bypasses LSC entirely. If the SD card was created from an FS03 project and inserted into an FS04 controller, the controller runs FS03-compatible code without the FS04 profile, and the same Online Monitoring symptom appears. Always re-create the SD card from the corrected FS04 project.

Troubleshooting Matrix

Best Practices for LOGO! Project Version Control

• Annotate every .lsc file with the target FS in the project name (e.g. PumpPanel_FS04_v1.3.lsc).
• Keep an engineering note per project stating the source FS and the migration date.
• After every controller firmware update, re-synchronize the LSC project with PC <-> LOGO! to read the current program back into LSC.
• Maintain a backup of the SD card contents (program and recipes) for each FS06 controller.
• Document the Modbus TCP map in a spreadsheet attached to the project — register, meaning, units, scaling, and which client uses which register — so future migrations do not need to re-discover the mapping.