Restoring LOGO! 8.4 Communication After Firmware v1.84.03

Restoring LOGO! 8.4 Communication After Firmware v1.84.03

Siemens LOGO! 8.4 base modules updated to firmware v1.84.03 (rendered as 18.4.3 on the onboard LOGO! display) can lose every Ethernet-based communication channel after the upgrade. Engineering teams have reported simultaneous failures of the integrated web server on TCP/80, Modbus TCP polling on TCP/502, and the S7 connection used by WinCC RT Advanced and TIA Portal HMI panels. This reference walks through the root cause, the full version-compatibility matrix for the LOGO! 8.4 toolchain, and the step-by-step recovery procedure that brings the LOGO! 8.4 stack back online without rolling back the firmware.

1. Problem Summary and Observed Symptoms

After a firmware update on a LOGO! 8.4 base module (BM) — either a single jump from v1.84.02 to v1.84.03 or the cumulative chain v1.84.01 → v1.84.02 → v1.84.03 — the following symptoms appear together:

• The integrated web server becomes unreachable on TCP/80 (or TCP/443 if HTTPS is enabled), even though the LOGO! still responds to ICMP ping and the Web Server user account remains activated in the project.
• Modbus TCP clients on TCP/502 receive "connection refused" or stop receiving updated register values; the BM still answers ARP but does not complete the TCP three-way handshake.
• WinCC RT Advanced and TIA Portal HMI runtimes lose the S7 connection; the HMI tag status toggles to connection fault or addressing error.
• LOGO! Soft Comfort V8.4 Online mode cannot establish a programming link over Ethernet, although the device is visible in Tools → Ethernet Connections.

Multiple field deployments confirm that enabling the web server user and the guest flag in LOGO! Soft Comfort is not sufficient to restore service after the firmware jump. The engineering software stack (LOGO! Soft Comfort V8.4 and LOGO! Web Editor V1.2) must also be on a release that recognizes the v1.84.03 project descriptor signature.

2. Affected Components and Firmware Versions

The following Siemens LOGO! 8.4 generation base modules are affected by the v1.84.03 communication handshake. Order numbers are listed at the family level; for a full breakdown of the 6ED1052 / 6ED1055 / 6ED1056 part numbers refer to the official Siemens LOGO! catalog.

Verify the installed firmware on the LOGO! BM via the onboard display menu System → Information → FW Version (the value shown on the display is 18.4.x — the leading 1. is dropped by the 7-segment rendering). Cross-check with the online diagnostic in LOGO! Soft Comfort V8.4 under Tools → Online Services → Diagnostics. Official firmware release notes are published on the Siemens Industry Online Support (SIOS) portal.

3. Root Cause Analysis

Firmware v1.84.03 introduces changes to the Ethernet service dispatcher that govern the HTTPS TLS handshake path and the Modbus TCP frame parser for compliance with the Modbus Application Protocol Specification V1.1b3. The new dispatcher requires the LOGO! Soft Comfort project to be saved in a circuit-diagram version whose project-header signature is recognized by the v1.84.03 firmware loader. When the engineering workstation is still running an older release of LOGO! Soft Comfort (for example V8.3.x or V8.4 build < 8.4.0_64) or an older LOGO! Web Editor (V1.0 / V1.1), the program pushed to the BM contains a project header that the v1.84.03 loader flags as unsupported revision.

The loader does not abort the transfer — it writes the program to non-volatile memory — but it leaves the S7 server socket, the Modbus TCP listener, and the integrated web server disabled because the project descriptor is not on the v1.84.03 allowlist. The IP stack itself remains up, which is why ICMP ping and ARP continue to work, but no application-layer TCP listener binds.

Independent confirmation in the field: when the firmware is updated first (LSC, LWE, and BM firmware in that order), the LOGO! remains reachable on TCP/80 for the v1.84.02 web pages until the next project transfer from a stale LOGO! Soft Comfort build. The first project download overwrites the previously cached web project bundle and re-breaks the web server. This is why reports of "we did not change the project, just updated the firmware" still result in a broken web server within hours. The project was not changed, but the project header is checked on every transfer.

4. Compatibility Matrix for the LOGO! 8.4 Toolchain

5. Pre-Upgrade Verification Checklist

Capture these values from the LOGO! before the firmware update so they can be restored after the recovery procedure.

1. Read the IP address, subnet mask, default gateway, and DNS server from System → Network on the LOGO! display, or via ipconfig /all on a PC on the same subnet. The factory default is 192.168.0.10 / 255.255.255.0 with gateway 192.168.0.1.
2. Export the LOGO! Soft Comfort project to a .lsc file (File → Export) and archive the generated *.lwe web project if a custom web visualization exists in the LOGO! Web Editor.
3. Document the S7 connection name in TIA Portal (HMI → Connections → name), the partner IP, the rack/slot, and the connection ID. LOGO! uses rack 0, slot 1, connection resource 02.
4. Record the Modbus TCP client configuration: polling interval, register ranges, function codes, and any scaling factors applied to analog values.
5. Document the activated web server user list and which user has the Administrator role versus the read-only role.
6. Photograph the BM display splash screen, the IP address, and the firmware version shown on the LOGO! for an audit trail.

6. Step-by-Step Recovery Procedure

Follow the steps in this exact order. Skipping ahead typically leaves the LOGO! in a half-restored state where the web server comes back but the Modbus TCP listener stays closed.

6.1 Update the Engineering Stack

1. Download the current LOGO! Soft Comfort V8.4 (build 8.4.0_64 or newer) from the Siemens Industry Online Support portal and install it on the engineering workstation. The installer replaces the older LogoSoftComfort.exe binaries in %ProgramFiles%\Siemens\LOGOComfort.
2. Install LOGO! Web Editor V1.2 from the same support portal. LWE V1.2 is the only release that can rebuild the web project bundle for v1.84.03 firmware.
3. If the project is integrated with a TIA Portal HMI (WinCC RT Advanced, WinCC Professional, Unified), confirm TIA Portal is at V17 Update 4 or newer (V18 / V19 recommended). Older TIA Portal versions do not import the v1.84.03 S7 partner descriptor.
4. Restart the engineering workstation. Some LOGO! Soft Comfort components register COM/DCOM handlers that are only refreshed on reboot.

6.2 Reconnect to the LOGO! and Verify the Firmware

1. Open LOGO! Soft Comfort V8.4 and select Tools → Ethernet Connections. Set the BM IP to the value captured in the pre-upgrade checklist. The default subnet is 192.168.0.x/24.
2. Click Connect. The dialog must report Device: LOGO! 8.4, FW: 1.84.03. If the version still reads 1.84.01 or 1.84.02, stop and re-run the firmware update using Tools → Firmware Update from the now-current LOGO! Soft Comfort.
3. Read the online diagnostic: Tools → Online Services → Diagnostics. Verify that Ethernet Status shows Link Up / 100 Mbps Full Duplex and that Socket Count reports at least one active listener (web server, Modbus TCP, or S7).

6.3 Transfer the Program to the BM

1. Open the exported .lsc project, then choose Tools → Transfer → PC → LOGO!. The transfer dialog must display the project-header signature as FW >= 1.84.03 compatible. If the dialog reports "Project revision older than firmware," the wrong LSC build is in use and step 6.1 must be repeated.
2. After transfer, the LOGO! restarts automatically. Wait 15 to 20 seconds for all three Ethernet services to bind.
3. Reconnect via Tools → Ethernet Connections and confirm that the S7 partner socket is now present — visible in the Online → Watch Table view.

6.4 Redeploy the LOGO! Web Editor Project (if used)

1. Open the existing *.lwe project in LOGO! Web Editor V1.2.
2. Choose Project → Rebuild Web Project. The V1.2 editor regenerates the static index.htm and the dynamic SVG pages with the v1.84.03-compatible web server tags.
3. Transfer the rebuilt project via Project → Transfer to LOGO!. The progress indicator should show Uploading ~/web/* 100%.
4. Clear the browser cache of every HMI client PC and the engineering PC before the first web server test. Stale index.htm from the v1.84.02 deploy is the most common reason "the web server is still broken."

7. Web Server User and Access Configuration

LOGO! 8.4 supports up to 8 web server users with role-based access. After a clean v1.84.03 install the user list is empty and every browser request returns HTTP 401 until at least one user is created.

Test the web server with the following command from a workstation on the same subnet:

A working v1.84.03 LOGO! returns HTTP/1.1 200 OK with Server: LOGO! 8.4 Webserver/1.84.03 in the response header. A HTTP 401 with body "Authentication required" indicates the user database is empty. A TCP connection refused on port 80 indicates the web server dispatcher was disabled by an incompatible project header — return to step 6.3 and re-transfer the program with the correct LSC build.

8. Modbus TCP Register Verification

The LOGO! 8.4 with v1.84.03 firmware exposes the following Modbus address spaces, identical to v1.84.02 except for two new function codes added to support 32-bit float transfers:

Function codes 0x14 (Read FIFO Queue) and 0x15 (Read File Record) are new in v1.84.03 and are not present in v1.84.02. They allow the LOGO! to serve 32-bit float values from the VM area without client-side word swap. Older Modbus masters that only support function codes 0x03 and 0x04 continue to work unchanged.

To verify the Modbus TCP listener is back, run the test query from a PC on the same subnet using modpoll or a Python Modbus client:

$ modpoll -m tcp -a 1 -r 1 -c 8 -t 0 -p 502 192.168.0.10
-- Polling slave...
[1]: 0
[2]: 0
[3]: 0
[4]: 0
[5]: 0
[6]: 0
[7]: 0
[8]: 0

A working v1.84.03 LOGO! returns a stream of zero or one values matching the current Q-output state. A timeout indicates the Modbus listener is still disabled — repeat step 6.3 with the corrected LOGO! Soft Comfort build. A "illegal data address" response (exception code 0x02) indicates the BM firmware is responding but the project memory layout has changed — re-check the VM mapping in Tools → Variable Memory Layout.

9. WinCC RT Advanced S7 Connection

WinCC RT Advanced connects to LOGO! 8.4 over an S7 connection using ISO-on-TCP (port 102). After the firmware update the connection is established by the HMI only if the TIA Portal project uses a LOGO! device descriptor compatible with v1.84.03.

Validation sequence after the recovery steps in section 6:

1. In TIA Portal, open the HMI project, then Devices & Networks → Connections. The "LOGO! 8.4" partner must be online; the green check mark in the connection table confirms the S7 partner is reachable.
2. Right-click the connection and run Check Consistency. TIA Portal V17 Update 4 / V18 / V19 reports No errors only when both the project descriptor and the BM firmware are aligned to v1.84.03.
3. Compile the HMI and start WinCC RT Advanced. The tag status bar should show the green connection icon within 30 seconds. If the icon stays gray, open Tools → Connection Diagnostics in the runtime to read the S7 error code (0x0001 = partner unreachable, 0x0002 = resource not available).

10. Verification Procedure

Run the following matrix end-to-end on the bench before putting the line back into production:

11. Rollback to Firmware v1.84.02 (if required)

If v1.84.03 must be left in place for upstream compliance but a downstream device cannot be updated in time, use the firmware rollback to v1.84.02:

1. Open LOGO! Soft Comfort V8.4 (build 8.4.0_64 or newer).
2. Connect to the LOGO! BM, then Tools → Firmware Update → Downgrade to V1.84.02. Confirm the warning dialog. The downgrade takes 60 to 90 seconds and reboots the BM.
3. Re-transfer the project from the same LOGO! Soft Comfort build. The project header is the same for v1.84.02 and v1.84.03, so no project change is required.
4. Validate the matrix from section 10 with the v1.84.02 expected values (e.g. Server: LOGO! 8.4 Webserver/1.84.02 in the response header).

Downgrading does not wipe the IP address or the user database, but it does reset the LOGO! to the factory program. The current LSC program must be retransferred after the downgrade completes. Document the BM, the firmware version, the LSC build, the LWE version, and the TIA Portal version in the audit log before the rollback so the firmware jump can be retried when the downstream equipment is updated.

12. Troubleshooting Matrix

FAQ