Troubleshooting SIMATIC Mode Time Synchronization Failures on CPU 417-5H with CP 443-1 and CP 1623

Time synchronization failures where a CPU 417-5H fails to synchronize in SIMATIC Mode from a WinCC OS Server over redundant Industrial Ethernet plant buses typically result from misconfigured synchronization direction on the CP 443-1 or redundant time frame collisions. To resolve this, configure the CPU as a Time Slave in HW Config, set the CP 443-1 to 'Accept time-of-day and forward' with direction set to 'From LAN to station' (without 'Use corrected time'), and ensure that only the primary active CP 1623 access point on the OS Server transmits time broadcast telegrams to avoid network frame contention.

SIMATIC Mode Time Synchronization Architecture on Industrial Ethernet

In SIMATIC PCS 7, plant-wide time synchronization ensures that alarms, trend archives, and batch records share a unified microsecond-accurate timeline. When operating with S7-400H controllers like the CPU 417-5H (6ES7417-5HT06-0AB0) equipped with external communications processors (CP 443-1 6GK7443-1EX30-0XE0), time frames are distributed across the plant bus.

In SIMATIC Mode (as opposed to standard NTP):
* The designated Time Master (a WinCC OS Server or SICLOCK hardware device) broadcasts SNAP-encapsulated time telegrams across the Industrial Ethernet subnet at regular intervals (typically every 10 seconds).
* The communications board on the OS Server (such as CP 1623 6GK1162-3AA00) transmits these frames directly from its dedicated firmware stack.
* The station's CP 443-1 intercepts the Layer-2 time frame and forwards the timestamp across the S7-400 backplane bus to synchronize the CPU real-time clock.

Root Causes of Controller Synchronization Failures

When the OS Server and OS Clients synchronize successfully but the AS controller fails to track the master time:
1. Direction Mismatch on CP 443-1: If the CP 443-1 is set to "From station to LAN", the communications processor expects the CPU to provide time rather than accepting it from the network.
2. "Use Corrected Time" Conflict: Enabling "Use corrected time" causes the CP to apply local timezone/daylight saving offsets, conflicting with PCS 7's requirement that AS clocks operate strictly in Coordinated Universal Time (UTC).
3. Dual CP 1623 Broadcast Collisions: In redundant plant buses with two CP 1623 cards in the same OS Server, enabling time transmission on both cards without proper access point segregation causes frame jitter and rejected sync packets.
4. MPI/DP Mode Overwrite: If the CPU clock properties are accidentally set to MPI Master, internal logic overrides incoming Ethernet frames.

Configuring AS Parameters - CPU 417-5H and CP 443-1

To establish deterministic time reception at the automation station:

[STEP 7 HW Config -> CPU 417-5H Properties]
   │
   ├─► Navigate to Tab: "Diagnostics/Clock"
   ├─► Synchronization:
   │     • In AS: Select "Slave"
   │     • On MPI: Select "None"
   └─► Click OK
         │
         ▼
[STEP 7 HW Config -> CP 443-1 Properties]
   │
   ├─► Navigate to Tab: "Time-of-Day Synchronization"
   ├─► Check: [x] "Accept time-of-day and forward"
   ├─► Direction: Select (•) "From LAN to station"
   ├─► Ensure: [ ] "Use corrected time" is UNCHECKED (PCS 7 runs in UTC)
   └─► Save and Compile HW Config -> Download to AS

This ensures the CP 443-1 acts as a transparent conduit passing incoming Ethernet time telegrams directly to the CPU 417-5H clock.

Configuring OS Parameters - CP 1623 and WinCC Time Synchronization

The following table details the required settings across engineering and operator station interfaces:

Interface / ComponentConfiguration DialogRequired SettingOperational RoleCP 1623 (Primary Port)PC Station HW Config -> CP 1623 Properties -> Time SyncCheck "Transmit time frames"Broadcasts SNAP time packets every 10s.CP 1623 (Secondary Port)PC Station HW Config -> CP 1623 Properties -> Time SyncCheck "Transmit time frames"Broadcasts on secondary redundant plant bus ring.WinCC Time SynchronizationWinCC Explorer -> Time Synchronization EditorEnable "Time sync via system bus"Declares WinCC OS Server as the plant Time Master.WinCC Access PointTime Sync Editor -> Access Point SelectionSet to CP1623(1)Defines primary communications endpoint.WinCC Computer PropertiesWinCC Explorer -> Computer Properties -> ParametersSelect "PLC is in UTC"Ensures HMI displays local time while AS runs in UTC.

Verification

To confirm that the CPU 417-5H is actively synchronizing with the OS Server:
1. In SIMATIC Manager, select the CPU 417-5H and open PLC -> Set Time of Day.
2. Observe the displayed CPU time; verify that the "Take from PG/PC" value matches the CPU internal clock within $\pm 10$ milliseconds.
3. Open the CP 443-1 Module Information -> Time-of-Day Synchronization tab; confirm that the status reads "Synchronized" and displays the MAC address of the transmitting CP 1623.
4. In WinCC Alarm Logging, verify that incoming process alarms display timestamps that align chronologically with controller sequence events.
5. In SIMATIC Manager Diagnostic Buffer, confirm the absence of "Time synchronization telegram lost" or clock drift warning entries.

Limitations and Operational Precautions

Never configure an automation station as a Time Master if an external hardware master (such as a SICLOCK TC 400) or an OS Server is already active on the same subnet. Conflicting time masters transmit competing timestamps, resulting in clock hunting, jumping trend coordinates, and severe database sequencing errors in SIMATIC BATCH.

Engineer FAQ

Why does PCS 7 mandate UTC for AS controller clocks?

Operating controllers in UTC eliminates time reversals and missing hours during Daylight Saving Time transitions, ensuring unbroken audit trails and deterministic batch recipes.

Can I use standard NTP instead of SIMATIC Mode for S7-400H?

Yes, CP 443-1 supports NTP. However, SIMATIC Mode achieves millisecond-level precision required for high-speed Sequence of Events (SOE) timestamping, whereas standard NTP on older CPs has higher jitter.

Why does enabling 'Use corrected time' cause problems?

'Use corrected time' applies the local timezone offset inside the communications processor, shifting the controller clock away from UTC and corrupting alarm logging timestamps.