Siemens LOGO! 7 IP Address Drift: Root Cause and Permanent Fix

Problem Statement: LOGO! 7 Spontaneously Changes IP Address and Gateway

A deployed Siemens LOGO! 7 (6ED1052-xxx08-0BA0 family, firmware 0BA7) is observed to migrate its Ethernet configuration without user intervention. The unit is configured statically with:

• IP address: 192.168.1.62
• Subnet mask: 255.255.255.0
• Gateway: typically 192.168.1.1

After an unpredictable interval (hours to days), the controller self-reports as 192.168.20.62 on a different subnet, and the gateway field also shifts. The peer LOGO! 8 on the same network continues to hold its IP without anomaly. No PC software, HMI, or remote client is intentionally writing to the LOGO! during the drift window. There is no other device on the plant network that advertises a 192.168.20.0/24 address block.

Because the LOGO! is a deterministic controller with no autonomous network configuration mechanism, the symptom points to one of three documented causes: an undetected restart that re-applies a different stored project, an SD card that overwrites the active program on power-up, or a hardware fault in non-volatile storage. This article walks through every documented mechanism for IP change, then provides a deterministic diagnostic and a permanent remediation path.

LOGO! IP Address Storage Architecture

The Ethernet configuration of a LOGO! 7 is persisted in two locations, both implemented as FLASH sectors managed by the LOGO! firmware:

Storage Region	Owner	Updated By	Survives Power Cycle
Project block (LSC file on internal flash)	LOGO! Soft Comfort (LSC) programming tool	Program transfer via Ethernet, SD card, or USB	Yes
Operator-modified parameters (IP, subnet, gateway, NTP, etc.)	LOGO! onboard edit menu	Front-panel menu or Web Config (only in STOP)	Yes

Per the LOGO! 7/8 system manual, the IP address field is part of the program block when the project is created in LOGO! Soft Comfort and is committed to non-volatile FLASH on each successful program download. The settings can also be edited from the LOGO! display only while the controller is in STOP state. There is no automatic update path: the field cannot be rewritten by SNMP, Modbus, a remote write from an HMI, a DHCP renew (LOGO! is statically addressed in this scenario), or a broadcast packet.

Reference: Siemens LOGO! 8 (0BA8) System Manual, entry ID 109751654. Although the source controller is a 0BA7, the IP persistence behavior described in the LOGO! 8 manual is identical to the 0BA7 generation as both share the same firmware architecture for Ethernet services.

Documented Mechanisms That Change a LOGO! IP Address

There are exactly four (4) mechanisms by which a running LOGO! can exhibit a different IP address than what was originally commissioned:

1. Onboard menu edit (STOP only): An operator navigates to Network > IP Address on the LOGO! display and changes the field. This requires the controller to be in STOP state, which is only possible if the user command STOP is sent, the mode selector is set to STOP, or the program halts.
2. Program transfer from LOGO! Soft Comfort: A new LSC program is downloaded from a PC over Ethernet. The transfer writes the entire project block, including IP, to FLASH.
3. SD card auto-load on power-up: If a micro-SD card is left in the slot, and that SD card contains a project file (BIN / LSC) with a different IP address, the LOGO! copies the program from the SD card into internal FLASH on every restart. This silent overwrite happens before the application logic starts.
4. FLASH corruption / hardware fault: A failed FLASH sector can cause the LOGO! to revert to a default or a previous-good configuration. This is rare but must be considered on aging hardware.

Mechanisms 1 and 2 require intentional user action. Mechanism 3 requires an SD card to be present, but the original commissioning team may have left the card in place after a previous upload and forgotten about it. Mechanism 4 is a fall-back hypothesis that should only be assumed after all other paths are excluded.

Root Cause Hypothesis: Undetected Restart with SD Card Auto-Load

The most plausible single explanation that fits the symptom pattern is:

The LOGO! 7 is experiencing periodic unplanned restarts (brownouts, voltage dips, EMC transients, or the operator pressing the mode selector). On each restart, a micro-SD card containing an older program (or a program authored on a different subnet such as 192.168.20.x) is auto-loaded, which overwrites the internal FLASH and silently changes the IP address and gateway.

Supporting evidence:

• Time-correlated: The IP change is intermittent, not instantaneous after each download. This pattern is consistent with periodic restart events rather than a continuous network write.
• Subtotal overwrite: Only the network parameters changed; the user's program logic otherwise continues to run. SD card auto-load is a full project replacement, but if the older project contains the same logic blocks with only the IP field different, the controller will appear functionally identical except for the network identity.
• Original commissioning procedure: The user reported performing a write to SD card operation through LOGO! Soft Comfort. That SD card is then the prime suspect if it remains inserted.
• LOGO! 8 unaffected: A peer LOGO! 8 with identical firmware age and same power environment continues to hold its IP, suggesting the issue is local to the LOGO! 7 (its SD card, its supply, or its specific hardware) rather than a network-wide event.

Diagnostic Method: M8 Initialization Flag with Remanent Counter

LOGO! Soft Comfort exposes a special boolean flag M8 (initialization flag / cold-start flag) that is forced to 1 for exactly one scan cycle at every cold start of the controller (power-on transition from OFF to RUN, or STOP-to-RUN). By feeding M8 into the count input of a remanent counter (a counter whose remanence / retention bit is enabled), the engineer can capture every restart event into a persistent count that survives the very restart being measured.

This is the recommended in-controller instrumentation because it leaves no external footprint and is observable from the LOGO! display, the Web Server, or a message text on the TDE.

Ladder Implementation (LOGO! Soft Comfort)

    M8 ----[ CU ]--- C001

  Block: Up/Down Counter (B001 in LOGO! terminology = C001)
    Input CU  := M8
    Input RES := (none, or wired to a discrete input for manual reset)
    Remanence: ON  (the counter value is retained across power cycles)
    Threshold: leave at default 1000000
    Output:    used as integer tag for display

Message Text Display

Place a Message Text block on the LOGO! 7 or the LOGO! TDE that shows the current value of C001. Suggested wording:

Restart counter = [ C001 ]

The engineer can then read this counter on the operator panel after any suspect period. If the counter increments by more than 1 over a working day where the user did not intentionally restart the LOGO!, there is an unintended restart event, and the IP shift is almost certainly caused by SD card auto-load or another startup-time configuration source.

SD Card Auto-Load Behavior in Detail

The LOGO! 7 / 8 supports a micro-SD card up to 32 GB (SDHC, FAT16/FAT32). On every power-up, the firmware checks the SD card root directory for known project filenames. The relevant auto-load rules:

File Found on SD	Action on Power-Up
LOGO_\*.BIN matching the firmware version	Silent copy of project from SD into internal FLASH, then boot
Empty SD card or no project file	Normal boot of internal FLASH project
SD card with incompatible firmware version	Project is ignored, boot from internal FLASH
SD card write-protected	Project is read but not transferred

The auto-load mechanism has no confirmation prompt and writes the SD-resident project to internal FLASH every time the LOGO! restarts. This is by design: it allows a field technician to perform a program update by powering a LOGO! with an SD card installed. However, it is a sharp edge if an SD card with a stale project is left in the slot. The remedy is immediate: remove the SD card and observe whether the IP drift ceases.

Power Supply and Brownout Considerations

LOGO! 7 and LOGO! 8 modules accept 24 V DC on the power terminals (LOGO! 24CE variants) or 115/230 V AC on the LOGO! 230RCE variants. The integrated Ethernet interface and the base unit share the same supply rail. Recommended operating limits:

Parameter	Min	Typ	Max	Unit
DC supply voltage (24V variant)	20.4	24.0	28.8	V DC
AC supply voltage (230V variant)	85	115/230	264	V AC
Brownout immunity	controller resets if V < ~18 V DC for > 50 ms			—

If the panel shares its 24 V rail with contactors, solenoids, VFDs, or any load that draws high inrush current, voltage dips below the brownout threshold will cause a cold restart of the LOGO!. Each cold restart triggers M8, increments the remanent counter, and (with an SD card installed) potentially overwrites the project.

Recommended fixes for a noisy supply:

1. Install a dedicated 24 V DC power supply (e.g., Siemens SITOP 6EP1334-3BA10) for the LOGO! and any HMI, separated from contactor / actuator supplies.
2. Add an AC-side surge protector on the 230 V input (if a 230 V variant is in use).
3. Add an EMI line filter on the 24 V DC input to attenuate high-frequency transients.
4. Verify the conductor gauge: voltage drop on long runs under load can dip below the threshold. Siemens recommends 1.5 mm² (AWG 16) for runs up to 10 m on the LOGO! power terminals.

Comparison: LOGO! 7 (0BA7) vs LOGO! 8 (0BA8)

The user's site has both a LOGO! 7 and a LOGO! 8. The fact that the LOGO! 8 is unaffected is informative. Key behavioral differences relevant to IP persistence:

Behavior	LOGO! 7 (0BA7)	LOGO! 8 (0BA8)
Ethernet interface	Integrated, 10/100 Mbit	Integrated, 10/100 Mbit
IP storage	FLASH (project block)	FLASH (project block)
SD card auto-load	Yes, on cold start	Yes, on cold start
Display access to IP edit	Yes, STOP only	Yes, STOP only
Web-based configuration	Available since 0BA7	Available
Typical firmware versions still in service	FS:04 to FS:06	FS:01 to FS:05 (and higher)
Default IP if no project loaded	192.168.0.10	192.168.0.10

The two generations share the IP storage model, so the differential symptom points to a project- or media-level difference (the SD card) rather than a firmware difference. See the official Siemens LOGO! 8 System Manual and the LOGO! product page for full generation specifications.

Step-by-Step Diagnostic Procedure

Execute the following in order. Each step either rules out a cause or sets up the next test.

1. Power down the LOGO! 7 and physically remove the micro-SD card from the slot. Inspect the SD card contents on a PC: open the card and check for any *.BIN or *.LSC files. If present, open the .BIN in LOGO! Soft Comfort (File > Open > select .BIN) and read the IP address from the project properties. If the SD-resident IP is 192.168.20.62, this is the cause. Archive the card, label it, and store it outside the controller.
2. Confirm the active LOGO! 7 project: with the SD card removed, connect LOGO! Soft Comfort to the LOGO! via Ethernet, perform an online > Identify LOGO! (or press the OK button on the display and navigate to Network) and verify the live IP is the expected 192.168.1.62. Then upload the program from the LOGO! (Online > Upload from LOGO!) and inspect the uploaded project's IP property.
3. Instrument M8 and a remanent counter as described above. Add a message text or use the Web Server to monitor C001.
4. Monitor for 48 hours with the SD card removed and the counter active. Record the C001 value at the start and end of the window. If the counter increments by more than 0, an undetected restart has occurred and the power supply is suspect.
5. Measure the 24 V DC supply with an oscilloscope or a data-logging multimeter (sample at 10 ms intervals) at the LOGO! power terminals. Look for excursions below 18 V DC lasting > 50 ms. Note any correlation with plant equipment switching.
6. Re-insert the original SD card only if Step 1 confirmed it contained the wrong project. After re-commissioning the correct IP and project, power-cycle the LOGO! once, then remove the SD card permanently. The SD card should not remain in the slot during normal operation unless it is the deliberate backup medium.

Resolution Methods

Resolution A: SD Card Removal (most common fix)

The reported resolution in the source incident was a re-write to SD followed by power-cycle. The underlying mechanism of that fix is that the freshly written card contained a project matching the user's intended IP 192.168.1.62, so the next restart overwrote the bad project in internal FLASH with the correct one. The correct long-term action is to remove the SD card so no future restart can re-apply an unintended project.

Resolution B: Disable SD Card Auto-Load Behavior

There is no firmware setting to disable SD card auto-load. The only way to prevent the SD card from overwriting the project is to keep it out of the slot. If an SD card is needed for a one-time program transfer, remove it immediately after the LOGO! has booted successfully.

Resolution C: Supply Stabilization

If the remanent counter increments after the SD card has been removed, the controller is brownout-restarting. The remedy is supply isolation: a dedicated Siemens SITOP PSU or equivalent, with the LOGO! on a circuit that does not share inrush loads with actuators.

Resolution D: Hardware Replacement

If the counter increments despite a clean supply and no SD card, the FLASH is suspect. Replace the LOGO! base unit. On the 0BA7 generation, common replacement catalog numbers are:

Catalog Number	Description
6ED1052-1MD08-0BA0	LOGO! 8 24CE, 8 DI / 4 DO, Ethernet, display
6ED1052-2MD08-0BA0	LOGO! 8 24CEo, 8 DI / 4 DO, Ethernet, no display
6ED1052-1CC08-0BA0	LOGO! 8 230RCE, 8 DI / 4 DO relay, Ethernet, display
6ED1052-2CC08-0BA0	LOGO! 8 230RCEo, 8 DI / 4 DO relay, Ethernet, no display

Cross-check the exact catalog number against the failing unit before ordering; refer to the Siemens LOGO! product catalog.

Verification Procedure

After applying any of the resolutions above, perform the following verification sequence:

1. Confirm the SD card is removed from the LOGO! slot.
2. Power-cycle the LOGO! once. Verify the IP remains at the configured value (e.g., 192.168.1.62) after the cycle.
3. From a PC on the same subnet, execute ping 192.168.1.62 -t for 10 minutes. Confirm continuous reply.
4. Read the remanent counter (C001). It should equal 1 if M8 fired once for the deliberate power cycle.
5. Wait 48 hours with no further operator action. Re-read C001; it must remain at the same value. The IP must remain 192.168.1.62 and the gateway must not change.
6. From the LOGO! Web Server (browser to http://192.168.1.62), log in (default credentials configured in the project) and verify the IP, subnet, and gateway fields. Compare with the project definition in LOGO! Soft Comfort to confirm parity.

If any verification step fails, return to Step 4 of the diagnostic procedure and check the supply rail with a logging instrument.

Related Issue: Logo TDE Returning to Factory Defaults After Reboot

Operators of the LOGO! Text Display (TDE) modules have observed an analogous symptom where the TDE reverts to factory language and time/date settings after a controller restart. This is by design (TDE configuration is not in the project block but is held in the TDE module's own volatile memory) but reinforces the diagnostic lesson: any user-visible state change after a restart indicates that a restart has indeed occurred. Apply the same M8 counter technique to confirm whether a restart is the root cause of any observed state drift, not just the IP address.

Best Practices to Prevent Recurrence

• Never leave an SD card in a deployed LOGO! 7 / 8 unless the card is the deliberate, controlled backup medium.
• Label SD cards physically with the project name, IP address, and revision date so a card with a stale project is identifiable.
• Source the LOGO! power from a dedicated, regulated PSU, not a shared 24 V rail with actuators.
• Lock the LOGO! mode selector to RUN position (if a hardware key is available) to prevent accidental STOP transitions that re-enable the menu edit path.
• Enable the LOGO! Web Server with a strong password so configuration can be inspected remotely without a site visit. Refer to Siemens LOGO! 8 System Manual for Web Server setup.
• Document the assigned IP, subnet, gateway, and revision in the cabinet, either on a label inside the door or as a fixed message text on the LOGO! display.
• Add M8 to a remanent counter as standard practice in every LOGO! 7/8 program you commission; the engineering cost is one block, and the diagnostic payoff is significant when an unexplained event occurs in the field.

Frequently Asked Questions