Problem Overview
The Siemens SIMATIC AS 410-5H CPU running firmware V8.1.0 inside a PCS7 V8.0 SP2 automation system has been observed to spontaneously enter DEFECTIVE mode. Once the CPU transitions to defective mode, it triggers an automatic full memory reset, drops its real-time clock to an illegal value, and then refuses to reload the user program on subsequent restart attempts. The fault is reproducible: in the affected plant all three AS 410-5H controllers in the project experienced the event at least once, while none of the AS 416 controllers in the same project have shown the failure. The 24 V load power supply of the defective station was verified healthy before and after the event, eliminating the most common cause of spurious CPU restarts.
This article walks through the diagnostic buffer cascade (events 277 → 278 → 286 → 287 → 288 → 289), the underlying root cause, and the field-proven recovery procedure. The recommended permanent fix is to leave firmware V8.1.0 and migrate to firmware V8.2.1 (or later) on every AS 410-5H in the project.
Affected System Configuration
| Component | Value as deployed |
|---|---|
| Engineering / Runtime system | SIMATIC PCS7 V8.0 SP2 |
| CPU family | SIMATIC AS 410-5H (single station, not redundant) |
| CPU firmware | V8.1.0 |
| Total CPUs in the project | 7 |
| AS 410-5H controllers | 3 (all three have failed at least once) |
| AS 416 controllers | 4 (none have failed) |
| Load power supply (PS 405 / PS 407) | Verified healthy — not the cause |
| Battery backup | Functional, no battery alarm in buffer |
The fact that the failure is isolated to the AS 410-5H subsystem is the most important diagnostic clue. The AS 416 family has a different firmware base and is not subject to this defect.
Diagnostic Event Cascade
The diagnostics buffer of the AS 410-5H shows a deterministic sequence that always leads with the consistency-violation event. Read the buffer bottom-up (oldest event first) to see the chain of causality.
| Event ID | Trigger order | Meaning (Siemens standard wording) |
|---|---|---|
| 277 | 1st | Inconsistency in the configuration data when checking parameters for internal consistency. No consistency entries assignable. Error type: time stamps of the loaded parameter fields do not match. |
| 278 | 2nd | Startup prevented — loading user program or internal inconsistency detected, SDBs < 200 incomplete, superfluous, or incorrect. |
| 286 | 3rd | Memory reset due to inconsistent data — issued approximately 4 minutes after event 289. |
| 287 | 4th | Time of CPU is illegal (RTC went out of range after the memory reset). |
| 288 | 5th | Time of CPU is illegal (subsequent RTC entry, redundant read). |
| 289 | Anchor | CPU went into DEFECTIVE mode. |
Root Cause Analysis
Event 277 is the root cause. The diagnostic text "time stamps of the loaded parameter fields do not match" means the system data blocks (SDBs) loaded from the flash / MMC area are no longer internally consistent: two or more SDBs that belong together reference different compilation timestamps. When the AS 410-5H runtime checks the SDB set at startup, it cannot build a valid module parameter image and refuses to enter RUN. The trigger is not a hardware defect on the CPU but a firmware defect in the way V8.1.0 validates parameter time stamps after a partial reload.
The remaining events are consequences:
- Event 278 — startup is blocked because the SDBs < 200 are incomplete or contradictory. The CPU halts in startup with the INT F LED on.
- Event 286 — because the CPU cannot recover a valid working database, the firmware forces a complete memory reset to fall back to a clean image.
- Events 287 / 288 — the buffer-backed RTC lost its time base across the reset. This is normal after a complete memory reset and not the underlying fault.
- Event 289 — after the reset the firmware again tries to validate the now-empty / partial image and the same validation defect puts the station in DEFECTIVE mode, which is non-recoverable without operator intervention.
The reason only the AS 410-5H CPUs are affected is that this validation path was introduced with the AS 410 firmware line. AS 416 firmware uses an older, more permissive SDB consistency check.
Memory Reset Mechanism Explained
The AS 410-5H supports two levels of memory reset that are relevant here:
| Level | How it is triggered | Effect on project data |
|---|---|---|
| Partial memory reset (MRES) | Mode selector to MRES, then back to RUN | User program deleted, SDBs < 200 retained |
| Complete memory reset | Firmware-internal trigger (event 286) or mode selector sequence | User program and SDBs < 200 deleted, CPU returns to factory SDB set |
Event 286 in this plant was a firmware-internal complete memory reset. The CPU invoked it on its own because the inconsistency in event 277 left no valid working image. After the reset, the project must be reloaded in full — a partial download is not sufficient, because the time-stamp mismatch recurs.
Immediate Recovery Procedure
The shortest path to bring the AS 410-5H back to RUN is the in-place consistency rebuild followed by a full download. This procedure does not require the CPU to be factory-reset and preserves the diagnostic buffer for the post-mortem.
- Open the PCS7 / STEP 7 project on the ES that owns this CPU.
- Open HW Config for the affected station.
- From the menu choose Station → Consistency Check. Resolve every reported inconsistency before continuing.
- Choose Station → Compile and Check All. Use the Compile and download objects dialog with "Compile and download entire station" selected.
- On the target CPU, ensure the mode selector is in RUN-P.
- From the ES, right-click the station and choose Download → Target System → Entire Station. Confirm the dialog that warns about overwriting the connection configuration.
- Watch the CPU LEDs: SF and BF should clear in < 30 s; the INT F LED must not appear.
- Verify in the online diagnostics buffer that no new entries of type 277, 278, 286, 289 appear for at least 30 minutes of observation.
If the consistency check is clean and the full download still returns the CPU to defective mode, proceed to the factory reset path.
Factory Reset Procedure (MRP)
The factory reset brings the CPU back to its as-delivered state. This is the correct escalation path when the in-place rebuild fails.
- Bring the process to a safe state and verify that the operator can take manual control.
- Open the front cover of the AS 410-5H and remove the buffer battery(ies) from the power supply module (PS 405 or PS 407). This prevents the diagnostic buffer and any residual RAM content from being retained.
- Set the mode selector to STOP.
- Using a thin screwdriver or a pin, press and hold the recessed RESET button on the CPU front panel for 5 seconds. The INT F LED begins to flash, then goes steady. Release the button.
- The CPU performs a self-reset to factory state; all project data is cleared.
- Re-insert the buffer battery(ies).
- Perform a full download of the cleaned and re-compiled project (not a partial one).
- Switch the mode selector from STOP to RUN-P and verify the CPU enters RUN without the INT F LED.
Firmware Update Procedure
The field-proven permanent fix for the event-289 defective-mode loop on AS 410-5H is firmware V8.2.1 or later. Siemens distributes firmware updates for the AS 410 family via the SIMATIC PCS7 software updates and via the Siemens Industry Online Support portal under entry ID 6ES7410-5HX08-0AB0. Plan the firmware upgrade as a separate maintenance window after the CPU has been brought back to RUN.
- Identify the exact order number on the CPU front panel (the AS 410-5H order number ends in
-5HX08for the generation in question). - From the Siemens support portal, download the firmware update file set for the matching order number. The package typically contains a
.updfile and a SIMATIC Manager add-on. - Copy the firmware package to the engineering station.
- Open SIMATIC Manager → Options → Firmware Update. Select the online AS 410-5H.
- Choose the downloaded
.updfile and start the update. The CPU reboots automatically; do not interrupt the 24 V supply during the update. - After the update, perform a full project download (do not rely on a partial download; the SDB time stamps have changed with the firmware).
- Verify the new firmware version in Online → Accessible Nodes → Module Information → Firmware.
Project Configuration Validation
Before declaring the station healthy, validate the project itself so that the firmware upgrade is not masked by an upstream engineering error.
| Check | Where | Expected result |
|---|---|---|
| Module consistency | HW Config → Station → Consistency Check | No errors |
| SDB time-stamp alignment | HW Config → Station → Compile and Check All | Single compilation time stamp across all SDBs |
| Connection configuration | NetPro → Compile | All connections bound, no "not connected" warnings |
| CPU protection level | HW Config → CPU → Protection | Level 1 or 2; avoid "cannot be overwritten" (level 3) for runtime projects |
| RTC battery voltage | CPU diagnostics buffer, byte for battery | OK |
| Operating mode after download | CPU front panel | RUN, no SF, no BF, no INT F |
Verification and Stability Test
Once the firmware is updated and the project reloaded, run a 24-hour stability test before returning the plant to full production. Use the following checklist:
- Export the diagnostics buffer at the end of the test and confirm that no entries of type 277, 278, 286, 287, 288 or 289 appeared.
- Force two controlled restarts (STOP → RUN-P) and verify that the CPU does not enter defective mode and that the RTC time survives the restart.
- Verify the SDB time stamps on the online CPU match the offline project (compare via Online → Module Information → Parameter).
- Repeat the test on every AS 410-5H in the project — the failure has been observed on every AS 410-5H in this plant, not only on the first one.
- Document the new firmware version and the date of the upgrade in the plant's PCS7 change log.
Troubleshooting Matrix
| Symptom | Most likely cause | First action |
|---|---|---|
| INT F LED steady after download | SDB inconsistency still present (event 277) | Re-run HW Config consistency check and full download |
| CPU enters defective mode after a partial download | Mix of old + new SDB time stamps | Full station download, not partial |
| RTC illegal immediately after a memory reset | Expected behavior; not a fault | Set the time via ES → Target System → Set Time of Day |
| Event 289 returns within minutes of recovery | Firmware V8.1.0 defect | Upgrade to firmware V8.2.1 or later |
| Event 289 on AS 416 after migrating from AS 410 | Different SDB set, check NetPro connections | Compile NetPro, full station download |
| SF LED on, no event in buffer | Distributed I/O fault, not CPU fault | Check PROFIBUS / PROFINET diagnostics of the slaves |
Why the AS 416 is Not Affected
The AS 416 CPU family belongs to the S7-400 generation and uses a different firmware branch. The SDB consistency check used by AS 416 firmware tolerates minor time-stamp skew between parameter fields. The AS 410 firmware branch was tightened in V8.1.0 to require strict equality of parameter-field time stamps, which is what triggers event 277 in projects that have undergone partial hot-edit downloads. Migrating AS 410-5H stations to firmware V8.2.1 restores tolerance to the same level as AS 416, eliminating the defective-mode path.
Field-Proven Caveats
- Always run the consistency check on the offline project before you touch the online CPU. Loading a partial fix on top of a project with broken HW Config will re-trigger event 277.
- If you have multiple AS 410-5H stations in the project, upgrade them all in the same maintenance window. Mixed firmware versions across stations are a known source of new event IDs that obscure the diagnostics buffer.
- The factory reset procedure wipes the diagnostic buffer. Export the buffer first if the root-cause analysis is still open.
- Do not rely on the front-panel INT F LED alone to determine whether the CPU has recovered. Always read the diagnostic buffer entries because event 277 can appear with the LED cleared in V8.1.0.
- Siemens' position on this generation is that PCS7 V8.0 SP2 with AS 410-5H is no longer in active development; an upgrade to PCS7 V9.0 SPx is the long-term remedy if the project allows it.
What does AS 410-5H defective mode (event 289) actually mean?
Event 289 means the CPU has detected an unrecoverable internal state — in this plant, a mismatch in the time stamps of the loaded parameter fields (event 277). The CPU stops normal operation and refuses to start until the project is fully reloaded or the CPU is factory-reset.
Is event 289 caused by the power supply or the battery?
No. In the reported case the 24 V load power supply was verified healthy and there is no battery alarm in the diagnostics buffer. The root cause is firmware V8.1.0's strict SDB consistency check, not a hardware fault.
Which firmware fixes the AS 410-5H defective-mode loop?
Firmware V8.2.1 or later. Field reports confirm that V8.2.1 eliminates the event-289 path on every AS 410-5H in the project, including all three stations that had already failed on V8.1.0.
Do I have to factory-reset the AS 410-5H after event 289?
Not always. Try the in-place recovery first: clean the project in HW Config, recompile, and perform a full station download. If event 289 returns, then perform the factory reset (battery out, RESET button held 5 s, full download).
Why are only the AS 410-5H CPUs affected while the AS 416 CPUs are not?
The AS 410 firmware V8.1.0 introduced a stricter check on SDB parameter-field time stamps. The AS 416 firmware branch does not enforce that check. The firmware V8.2.1 update for AS 410 brings the validation tolerance back in line with the AS 416 behavior.
Can I leave the AS 410-5H on firmware V8.1.0 and live with the event-289 risk?
Not recommended. Once event 277 is logged the CPU is on borrowed time; event 289 can occur at any subsequent restart. For a continuous process the safe path is firmware V8.2.1 or later, plus the long-term PCS7 version upgrade.