Troubleshooting WinCC S7-400 Disconnection Error 0xFFDF 410E and DataManager Queue Overflow

1. Problem Overview

A WinCC V6.2 SPx client-server installation with SIMATIC S7 Protocol Suite v6.2 experiences a sudden runtime freeze at the server, leaving clients unable to acquire process values from an S7-416-2DP controller. The log trail shows a brief PLC disconnection, followed by a DataManager update queue overflow, a forced project deactivation by the WinCC Project Manager, and a fail-over attempt against a redundant server that has been offline for approximately one month. Operators observed values frozen for more than 30 minutes before manual server restart.

The fault is composed of three coupled events:

1. A short ISO-on-TCP disconnect from the S7-416-2DP reported as S7 error code 0xFFDF 410E in SIMATIC_S7_PROTOCOL_SUITE_01.LOG.
2. A DataManager Runtime queue saturation of 1,048,696 bytes (against a configured high-water mark of 1,048,576 bytes) reported as event 1000200 in WinCC_Sys_02.log.
3. An unscheduled project deactivation triggered by the WinCC Project Manager after the CCAlgRtServer.exe process did not stop within its timeout window.

This article decodes each log line, explains the underlying mechanisms, and provides a step-by-step recovery path including the use of WinCC Channel Diagnosis and the S7-400 diagnostic buffer.

2. System Architecture and Path of Failure

The installation follows the standard WinCC server/redundant server/client topology:

• BIO-SRVR01 – active WinCC server, host name used in every WinCC_Sys_02.log entry.
• BIO-SRVR02 – redundant partner, powered down for maintenance and not yet re-synchronized.
• WinCC clients – engineering and operator stations subscribing to the server.
• S7-416-2DP – automation station, accessed through the SIMATIC S7 Protocol Suite over ISO-on-TCP (port 102).

Failure path summarized in the topology diagram below.

When the S7 connection breaks, the DataManager temporarily stores pending updates in a memory queue. If the queue length exceeds the high-water mark, the system raises event 1000200 and begins discarding update telegrams. The redundant partner cannot take over because it has been administratively down longer than the configured archive synchronization window.

3. Decoding the Log Files

3.1 SIMATIC_S7_PROTOCOL_SUITE_01.LOG

The channel unit log is the authoritative source for S7 transport errors. The relevant lines are:

2008-11-20 12:25:32,108 INFO  S7 channel unit "TCP/IP" activated!
2008-12-15 03:16:52,000 ERROR Connectionerror 1 "S7-416-2DP": Errorcode 0xFFDF 410E!
2008-12-15 05:31:18,781 INFO  Log starting ...

Interpretation:

• 03:16:52 – The channel reports the S7 connection to logical connection 1 (S7-416-2DP) as broken.
• 0xFFDF 410E – Vendor-neutral S7 error code 0xFFDF is the high word returned by the SIMATIC driver; the low word 0x410E decodes to ISO-on-TCP error class 41 / event 0E – "connection aborted by remote partner or partner reset".
• 05:31:18 – New log file started after a manual service restart (gap is 2 h 14 min).

3.2 WinCC_Sys_02.log

This is the global WinCC runtime log. CSV fields are Severity,Date,Time,EventID,Category,User,Computer,Application,Message.

3.3 Format error of tag 'TRENDING_A'

The earlier entry on 24.11.2008:

Format ID 0x08200000 is the WinCC internal type mask for a text reference (8-bit) tag with a 32-byte length and a "right-justified, no zero-fill" qualifier. Event 1000005 is raised when the tag's runtime type no longer matches the configured archive/display type. The most common root causes are:

• Renamed the tag in WinCC Explorer without updating the trend/table view bound to it.
• Re-imported tags from a STEP 7 project and the data type changed from WORD to INT.
• Migrated the project to a higher WinCC version that reinterprets 8200000 as a different type.

This error is a long-standing configuration problem and is independent of the 15.12.2008 outage, but it confirms the project has accumulated type-mismatched tags and should be reviewed.

4. S7 Error Code 0xFFDF 410E Explained

The S7 communication driver (S7ONLINE / S7DOS) returns compound error codes. The structure is:

ErrorCode = (VendorError << 16) | S7Error
  S7Error      = 0x410E  -> ISO-on-TCP: "connection reset by peer / partner not reachable"
  VendorError  = 0xFFDF  -> "internal S7DOS channel error class"

The exact string reported is 0xFFDF 410E where the leading FFDF is interpreted as the S7-400 / S7-300 high-level error class "Connection Failure" and the low word 410E specifies "partner actively reset the TCP connection". Common on-site triggers:

• An HMI/PG ran an online STEP 7 download that briefly tore down all S7 connections.
• The CP 443-1 or the on-board PROFINET/IE interface of the S7-416-2DP was reinitialised (e.g. after a firmware update or restart of the network stack).
• A firewall or managed switch silently dropped TCP port 102 sessions.
• The CPU was placed in STOP, then back to RUN, which closes and reopens ISO-on-TCP connections.

The companion event 1000204/1000205 in WinCC_Sys_02.log confirms the WinCC channel detected the disconnect and reconnected within 359 ms. The channel itself is therefore healthy.

5. DataManager Update Queue Mechanics

The DataManager Runtime maintains an in-memory queue for unprocessed update telegrams between the channel DLLs (e.g. SIMATIC S7 Protocol Suite) and the archive/tag-notification layer. The queue is sized by the registry key:

[HKEY_LOCAL_MACHINE\SOFTWARE\Siemens\WinCC\RT\DataManager]
"QueueHighWaterMark"=dword:00100000      ; 1 048 576 bytes (default)
"QueueLowWaterMark" =dword:000C8000      ;   819 200 bytes (default)
"UpdateCycle"       =dword:000003E8      ; 1 000 ms acquisition cycle

The logged values match the WinCC V6 defaults exactly:

• High water mark = 1 048 576 bytes (1 MiB).
• Low water mark = 819 200 bytes (800 KiB).
• Actual queue size at the time of the event = 1 048 696 bytes (120 bytes over the high-water mark).

When the actual size exceeds the high-water mark, the DataManager raises event 1000200 and discards pending updates until the queue drains below the low-water mark. Sustained overflow indicates that the application consuming the updates (archives, scripts, trend controls) cannot keep up with the acquisition rate.

6. Project Manager Shutdown Cascade

The Windows service CCProjectMgr watches WinCC runtime processes. When it receives a stop signal (e.g. from the operator clicking "Deactivate Project"), it sends WM_CLOSE to each process. If a process does not terminate within the configured timeout (default 30 000 ms, registry StopTimeout), it issues an APPL STOP FAILED followed by TERMINATE (TerminateProcess). The recorded sequence:

05:20:52  TIMEOUT         ; CCAlgRtServer.exe did not stop in time
05:22:46  APPL STOP FAILED ; Project Manager escalates
05:22:46  TERMINATE        ; WinCC issues TerminateProcess
05:36:06  Outage detected  ; RedundancyAgent sees the master drop offline

The fact that CCAlgRtServer.exe (the alarm logging runtime) ignored a graceful stop for nearly two minutes is a strong indicator of a deadlock inside the alarm logging DLL, often caused by:

• A script action that calls MSRT or COM objects whose STA is hung.
• A blocking database call against an unreachable SQL Server.
• A third-party OPC/Channel DLL that holds a critical section.

7. Redundancy Implications

Event 1012200 "Outage detected, reason 'ProjectDeactivated'" means the RedundancyAgent interpreted the project deactivation as a hard failure of the master. It raised an outage on the partner. Event 1012226 "Redundant partner is in runtime mode" 5 h 23 min later shows the operator manually reactivated the project on BIO-SRVR01 (not BIO-SRVR02), proving the partner was not promoted automatically.

The redundancy configuration must be reviewed against the following points:

1. The partner was offline for ~30 days. WinCC V6.2 discards the mirror image if the archive gap exceeds the configured ArchiveSynchronizationTime (default 60 min). A re-sync must be performed with the partner online.
2. The fail-over algorithm is heartbeat-based (default 1 s). The 5 h 23 min gap between 1012200 and 1012226 shows the heartbeat survived, but the partner never started. This is expected if the partner was administratively down.
3. Event 1012201 "End of outage" is raised on the master after the project is reactivated. The master always re-asserts itself; it does not yield to the partner after recovery.

8. S7-400 CPU Diagnostic Buffer Examination

The first response to a 0xFFDF 410E is to read the diagnostic buffer of the S7-416-2DP. Use STEP 7 V5.5 (or TIA Portal V13+) on an engineering PG and connect to the CPU either online via the same Ethernet subnet or via the CP 443-1.

1. Open the project containing the S7-416-2DP station.
2. Select the CPU in the project tree and choose Target system > Diagnostic buffer (German: Zielsystem > Diagnosepuffer).
3. Filter the time range to 15.12.2008 03:16:00 - 03:18:00.
4. Look for the following events, in order of likelihood:

If the diagnostic buffer shows OB 85 / OB 86 not loaded, you must insert and download the missing OBs. This is one of the most common production-line causes of overnight S7 disconnects.

9. Step-by-Step Recovery Procedure

9.1 Preconditions

• WinCC V6.2 SP2 or higher installed on BIO-SRVR01 (see section 10).
• STEP 7 V5.5 with the S7-400 hardware support package installed on an engineering PG.
• Administrator account on BIO-SRVR01 and BIO-SRVR02.
• Access to the S7-416-2DP online via Ethernet.

9.2 Procedure

1. Capture the live state. Start WinCC Channel Diagnosis from the Windows Start menu: All Programs > Siemens Automation > WinCC Channel Diagnostics. Click the connection S7-416-2DP and then the gear-wheel icon to dump the current connection state. Save the screenshot to \\BIO-SRVR01\WinCCProj\Diagnostics for post-incident review.
2. Read the S7-400 diagnostic buffer. Use STEP 7 as described in section 8. Note the time-stamped events between 03:16:00 and 03:18:00.
3. Check the channel log. Open SIMATIC_S7_PROTOCOL_SUITE_01.LOG in the project directory. Confirm that the only error class is 0xFFDF with low word 410E or 4101. Repeat for every additional connection.
4. Stop the WinCC runtime cleanly. In WinCC Explorer, right-click the project and choose Deactivate project. Wait for CCAlgRtServer.exe, CCArchiveServer.exe, and CCProjectMgr.exe to terminate within 30 s. If any process exceeds the timeout, capture a user-mode dump with procdump -ma CCAlgRtServer.exe for offline analysis.
5. Recompile and reload the OS project. Open WinCC Explorer, choose Tools > Project Duplicator and create a backup. Then choose Project > Compiler > All to rebuild the C scripts. This clears the 1000005 format error for TRENDING_A if the data type was changed in STEP 7.
6. Adjust the DataManager queue (only if overflow is recurring). Open the registry editor and navigate to HKLM\SOFTWARE\Siemens\WinCC\RT\DataManager. Set QueueHighWaterMark to 0x00200000 (2 MiB) and QueueLowWaterMark to 0x00180000 (1.5 MiB). A 100 % increase is the practical maximum for a 32-bit V6.2 server; going higher will not improve behaviour because the bottleneck is downstream.
7. Re-synchronise the redundant server. Power on BIO-SRVR02 and start WinCC. Open Redundancy > Partner status on both servers. Run Project > Archive Synchroniser on the master. Wait for the Archive synchronised status line.
8. Restart runtime and verify. Activate the project on BIO-SRVR01. Watch WinCC_Sys_02.log for ten minutes. No new 1000200 entries and a stable S7 connection confirm the fix.

10. Firmware and Software Update Considerations

WinCC V6.2 (without SP) ships several known issues that are resolved in SP2 and SP3:

SP2 is useful, but for a long-lived V6.2 system the supported migration path is to install the latest hotfixes from the Siemens WinCC V6.2 Hotfix DVD. SP2 alone does not include all redundancy fixes; combine it with hotfix KB 16622456 and any later dated hotfixes listed in the support entry.

11. Verification Checklist

After applying the recovery procedure, verify the following:

• SIMATIC_S7_PROTOCOL_SUITE_01.LOG contains no ERROR entries for 72 h.
• WinCC_Sys_02.log contains no 1000200 entries for 72 h.
• CCAlgRtServer.exe terminates within 30 s of Deactivate project.
• Channel Diagnosis shows connection state Connected with last error time stamp older than 72 h.
• S7-400 diagnostic buffer shows no OB85 / OB86 missing events.
• WinCC clients receive updated values within one acquisition cycle (typically 1 s).
• Redundant partner status shows Archive synchronised continuously.

12. Preventive Measures and Hardening

1. Load all S7-400 error OBs. Add OB 80, OB 82, OB 85, OB 86, OB 121 and OB 122 to the S7 program. Empty OBs contain a single BE and prevent the CPU from going STOP on transient I/O or rack faults.
2. Reserve CPU resources for the S7 connection. Set the S7-400 connection resources to at least 16 (default 8) via HW Config → CPU properties → Communication. The SIMATIC S7 Protocol Suite uses one connection per logical connection; a typical installation with 4 connections therefore requires 4 resource blocks plus reserves.
3. Stagger the DataManager update cycles. If the project uses 1 000 ms everywhere, redistribute the loads to 800 / 1 200 / 2 000 ms to avoid simultaneous archive writes.
4. Move the SQL archive to a local SSD. Network shares (SMB / NFS) over WAN links are the most common cause of 1000200 on systems that were otherwise healthy.
5. Monitor the Update data lost counter via WinCC Performance tags. Expose the high-water mark and the lost-update count to the operator screen and raise an alarm when the queue exceeds 80 % of the high-water mark.
6. Keep the redundant partner online. A partner that is offline for longer than the ArchiveSynchronizationTime (default 60 min) will not be promoted automatically. Schedule a re-sync window in the maintenance plan.
7. Patch WinCC V6.2 to the latest hotfix collection. Siemens continues to ship hotfixes for V6.2 customers who have not migrated to V7.x.

13. Frequently Asked Questions