S7-412H FLASH Download: Resolving Error 8402 STOP Mode

1. Problem Statement

An S7-412H CPU enters STOP immediately after a project is downloaded to a FLASH (FEPROM) memory card. The STEP 7 diagnostic buffer records event {8402} with the message "Service cannot be performed owing to state of addressed object", and the CPU does not transition to RUN. The download itself completes without an explicit error, so the failure only surfaces when the operator selects the RUN pushbutton or the PG issues a RUN operating-mode request.

This symptom is specific to the S7-400H family because both CPUs of the redundant pair must hold a consistent image of the project. A successful transfer to one CPU is therefore not sufficient. Event 8402 is the way STEP 7 reports that the addressed logical object (CPU, slot, OB, or DB) is in a state that cannot accept the requested service at that instant. The S7-400H System Manual should be the working reference for any H-station change.

2. S7-400H Architecture and CPU 412H Specifications

The S7-400H is a fault-tolerant station built from two CPUs in a single logical rack. The 412H is the entry-level member of the H range. The H suffix indicates the CPU is designed to operate as a redundant pair. The table below summarizes the engineering data that matters for FLASH operations on this CPU family:

The two physical interfaces at the bottom of the CPU are reserved for redundant communication with the partner CPU. Without functioning sync modules and an unbroken fiber-optic loop, the pair cannot complete the link-up sequence and the system remains in STOP with a diagnostic event in the buffer.

3. FLASH Memory Card Types and Order Numbers

For the S7-412H, the FEPROM card sits in the slot at the top of the CPU. FEPROM retains the program across power loss and does not require a battery. RAM cards are also supported on the CPU 412-3H as a load-memory option, but the production workflow is almost always FEPROM-based for H systems. Note that the card catalog is shared with the rest of the S7-400 family:

4. Decoding Diagnostic Event 8402

STEP 7 writes diagnostic events in the buffer using either the format Wx:yy:zz or a bracketed numeric ID. The {8402} ID belongs to the asynchronous "Operating State" event class. The standard messages associated with 8402 on the S7-400 family include:

• "Service cannot be performed owing to state of addressed object"
• "Operating mode transition not possible"
• "Memory object locked by H system"

To read the event, open the online CPU in SIMATIC Manager, choose PLC > Diagnostics/Settings > Diagnostic Buffer, and sort by date/time. The {8402} entry typically appears with the "Mode" tab indicating a STOP transition caused by the partner CPU. The same buffer often shows the related event ID of the underlying fault (for example 73:01 fail for a broken link-up, or 4xx3 for an OB start information error). Treat the 8402 line as the symptom; the line directly above it is the cause.

5. Root Cause Analysis: Why the CPU Stays in STOP

Five root causes account for the overwhelming majority of {8402} entries after an FEPROM download on a 412H. Address them in the order shown.

5.1 Asymmetric download to only one CPU

STEP 7 by default transfers the program only to the CPU the PG is online with. The partner CPU retains the previous program or has an empty load memory. During the start-up sequence the partner CPU signals a configuration mismatch, and the system locks mode changes to protect process state. This is the most common cause of 8402 on H systems.

5.2 Module address mismatch in HW Config

The SF LED of the partner CPU will be lit if any module in the actual rack topology has a slot address that differs from HW Config. The diagnostic buffer reports the offending slot. The S7-412H treats the redundant project as a single logical rack; a mismatch on a single slot blocks all operating-mode transitions.

5.3 Sync module or fiber-optic failure

When the sync module IF LED is off or flashing at 0.5 Hz, the link-up phase is interrupted. The CPU stays in STOP because the redundant partner is not online. Sync module failure on the S7-400H is reported as event ID 73:43 or 73:0A in the diagnostic buffer.

5.4 Wrong FEPROM card type or damaged card

FEPROM cards have a small write-protect slider. If the slider is set, the CPU cannot write the new program. A card that has been used in a different CPU family (for example, an S7-300 MMC) will not seat correctly and the CPU reports "Memory card error" instead of completing the download.

5.5 FEPROM download issued while the CPU is still in RUN

When PLC > Download User Program to Memory Card is selected while the CPU is in RUN, STEP 7 may leave the CPU in a transient state. The operating mode button is then disabled and the CPU rejects the RUN command. This produces a 8402 entry with the additional text "Operating mode change in progress".

6. Hardware Configuration Verification

Before any new download, validate the rack topology from the PG.

1. Open SIMATIC Manager and select the project with the offline S7-400H station.
2. Double-click Hardware to open HW Config.
3. Click the Accessible Nodes icon on the toolbar. Confirm that both CPUs (rack 0, slot 3 for CPU 0 and slot 4 for CPU 1, or per your project layout) appear with the correct MPI/DP or PROFINET addresses.
4. Cross-check the slot, order number, and firmware version of every module in the online topology against the offline configuration. Any red "?" in the comparison column indicates a mismatch.
5. Right-click the H station and choose Save and Compile to regenerate the system data. Without this step, downloads made from a project opened in a second SIMATIC Manager session may silently skip the system data blocks (SDBs).

7. Step-by-Step FLASH Download Procedure for S7-400H

The procedure below writes the entire user program to the FEPROM card and brings both CPUs back to RUN. Run this with a direct MPI or Ethernet connection to CPU 0 of the pair; the redundant transfer to CPU 1 is handled by the H system.

7.1 Prerequisites

• Both CPUs in STOP. The MODE switch is in the RUN position; use the PG command PLC > Operating Mode > STOP to stop the partner if necessary.
• Sync modules and fiber-optic cables installed and seated (IF LED green, never red).
• Battery- or UPS-backed power to the rack. FEPROM write operations are non-recoverable on power loss.
• FEPROM card physically present in CPU 0 only. Insert the card into CPU 1 only when CPU 0 has finished writing.

7.2 Procedure

1. In SIMATIC Manager select the H station (offline view).
2. Choose Options > Edit H Station or use PLC > Download to Target System. For first-time FEPROM programming, choose Download to Memory Card from the PLC menu instead of the regular download.
3. STEP 7 will stop the target CPU and offer the option to overwrite existing blocks. Accept the overwrite if the FEPROM contains a previous version of the program.
4. Wait for the dialog Download to Memory Card completed. The CPU LEDs M (Modify) and BATF (Battery Fault) will be off when the write finishes. The FEPROM card must not be removed while the FRCE or LINK LEDs are flashing.
5. Repeat the same download sequence against the partner CPU. On a 412H, the system performs this automatically when the H-station download function is used; if the partner CPU is not visible in Accessible Nodes, address it directly via its MPI/DP or PROFINET node number.
6. From the PLC menu, choose Operating Mode > RUN. The S7-412H performs the link-up, then the redundant update, then transitions both CPUs to RUN. The buffer should show the events in the order 73:01 (link-up OK), 73:02 (update OK), 0x30 (operating state RUN).

8. H-System Synchronization After a New FEPROM

An H station whose FEPROM cards have just been re-flashed must be re-linked before the partner CPU can update. The H system performs this automatically, but a manual link-up is sometimes required when one CPU has been replaced.

1. Set the MODE switch of both CPUs to RUN-P (or STOP if a start-up OB needs to be skipped).
2. With the PG online to CPU 0, run PLC > H System > Link Up.
3. Wait for the link-up to complete (LINK LED steady green on both CPUs). Typical time: 30 to 90 s, depending on user program size and the configured monitoring time.
4. Run PLC > H System > Update if the partner CPU holds an older program revision. The new program is copied from CPU 0 to CPU 1 over the fiber-optic link.
5. Switch the system to RUN. Confirm that Diagnostic Buffer on both CPUs shows the entry "Operating state changed to RUN" with event ID 0x30.

9. Verification and Commissioning

Confirm the following after the download:

• RUN LED on both CPUs is green and steady.
• LINK LED on both CPUs is steady green (link-up complete).
• IF LED on the sync modules is green (interface OK).
• SF / BF / BATF LEDs are off on both CPUs.
• Diagnostic buffer last entry on both CPUs: "Operating state changed to RUN", event ID 0x30.
• Accessible Nodes shows both CPUs with status "RUN".
• Force table state matches the post-update configuration. Force values from a previous FEPROM image are not retained across a full FEPROM write.

10. Troubleshooting Matrix

11. Field-Proven Caveats

• STEP 7 V5.5 SP2 ships an outdated HW catalog for the 412H. Install the most recent Hardware Support Package (HSP) before the first download; otherwise the partner CPU may appear with "—" in Accessible Nodes even when the rack is healthy.
• Do not pull a FEPROM card while the CPU M LED is on. A write operation interrupted by a hot swap permanently corrupts the card image; the next start-up produces a 8402 / 4xx3 pair that does not recover on its own.
• An S7-412H project that has been migrated to a 414-3H or 416-3H must be re-flashed on the new CPU. A 412H FEPROM is not accepted by the larger CPU and yields a {8402} entry with "CPU family mismatch".
• If the rack contains any IM 153-2 redundant I/O, the FEPROM download must include the I/O station's GSD revision. A mismatch stalls the link-up phase and surfaces as 8402 after the start-up attempt.
• Watch the monitoring time of OB 80 / OB 121. A long S7-400H project can exceed the default 100 ms time slice; if the system enters STOP during the FEPROM commit, the buffer shows {8402} followed by 4xx4 "OB not loaded".
• For PG-to-CPU cabling, prefer Ethernet (ISO-on-TCP) over MPI for large FEPROM images. The 187.5 kbps MPI default can push a 32 MB FEPROM write past the S7-400H connection-monitoring window, which is one of the ways an otherwise valid download still leaves a 8402 entry in the buffer.

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