Resolving Time Synchronization Failure Between CPU 410-5H (Master) and CP 1623 (Receiver) in SIMATIC PCS 7

In SIMATIC PCS 7 (v8.1 SP1 and v8.2), when the automation controller (CPU 410-5H) is configured as the plant bus Time Master and the Operator Station's CP 1623 communications processor acts as the Time Receiver, synchronization failures and persistent warning messages occur if the PC Station hardware configuration has not been compiled and downloaded to the OS. To resolve this, engineers must configure 'In SIMATIC mode (as receiver)' under the CP 1623 properties in the PC Station HW Config, download the station configuration via the Station Configuration Editor, and bind WinCC Time Synchronization to the CP1623(ISO) access point.

Plant Bus Time Synchronization Architecture - SIMATIC Mode vs NTP

In SIMATIC PCS 7 high-availability and distributed architectures, time synchronization ensures consistent Sequence of Events (SOE) timestamping across controllers and operator stations:
- SIMATIC Mode (Ethernet Broadcast / SNAP):
* Operates at Layer 2 of the OSI model using ISO-compatible SNAP broadcast frames.
* When an S7-400 or CPU 410-5H controller is designated as the Time Master, its integrated Industrial Ethernet interfaces or communications processors (CP 443-1) transmit periodic time-of-day broadcast telegrams (typically every 10 seconds) containing Coordinated Universal Time (UTC).
- CP 1623 Communications Processor:
* A dedicated PCI Express communications processor equipped with an onboard microprocessor running firmware that offloads communication tasks from the PC host CPU.
* In time slave mode, the CP 1623 hardware clock synchronizes directly to the SIMATIC broadcast frames, guaranteeing high-precision 1 ms time stamps for process alarms.
* Unlike standard office network interface cards (NICs), the CP 1623 requires explicit hardware parameter assignment via STEP 7 HW Config.

Root Cause of CP 1623 Time Reception Warnings

The synchronization failure and warning prompt typically manifest in the following engineering sequence:
1. Configuring CPU 410-5H as Master:
- In HW Config, under CPU properties > Diagnostics/Clock, the synchronization mode on the MPI/DP or PN interface is set to As Master with an interval of 10 seconds.
2. The Undownloaded PC Station Trap:
- The engineer configures the CP 1623 in the OS PC Station's HW Config but only compiles the WinCC OS project without performing a physical Station Download to the target PC.
- The CP 1623 continues running with factory default parameters where SIMATIC time synchronization is disabled.
- The OS station detects time broadcast frames on the physical wire but its CP hardware refuses to lock onto the signal, generating error entries in the SIMATIC NET diagnostics buffer:
text Time synchronization failed: No valid time master detected on CP 1623.
3. Disappearance After Download:
- Downloading the PC Station configuration (Station > Download) transfers the system data blocks into the local Station Configuration Editor (s7onlinx.exe), initializing the CP 1623 clock receiver and clearing the warning.

Step-by-Step Configuration and Download Workflow

Follow this procedure to establish deterministic time synchronization:

Configure CPU 410-5H as Time Master in HW Config:
- Open HW Config for the AS station.
- Double-click the CPU 410-5H. Navigate to Diagnostics/Clock.
- Under Synchronization mode, set In AS to None and On MPI/DP to As Master.
- Open properties of the integrated PROFINET interface (X1 or X2), navigate to Time-of-Day Synchronization, and check Enable time-of-day synchronization in SIMATIC mode.
- Select As Master with an interval of 10 seconds.
Configure CP 1623 in the PC Station HW Config:
- In SIMATIC Manager Component View, open HW Config for the SIMATIC PC Station (OS Server).
- Double-click the CP 1623 in the rack.
- Navigate to the Time-of-Day Synchronization tab:
- Check Activate time-of-day synchronization.
- Select In SIMATIC mode (as receiver / slave).
- Save and compile the PC Station HW Config.
Download Hardware Configuration to OS PC Station:
- In HW Config, select Target System > Download to Selected Station.
- Ensure the target computer name and IP address match the physical machine.
- The Station Configuration Editor reloads components and places the CP 1623 into RUN mode.
Bind WinCC Time Synchronization Access Point:
- In WinCC Explorer, double-click Time Synchronization.
- Check Synchronization via plant bus.
- Set Access point 1 to CP1623(ISO).
- Click OK and restart WinCC Runtime.

Time Master and Receiver Configuration Parameter Table

The following table details synchronization parameters for CPU 410-5H and CP 1623:

Subsystem ComponentHardware Configuration LocationOperational ParameterRequired SettingCPU 410-5HHW Config > CPU > Diagnostics/ClockClock SynchronizationAs Master (Interval: 10s)CPU PN Interface (X1/X2)HW Config > PN-IO > Time SynchronizationProtocol FormatSIMATIC Mode (As Master)CP 1623 (PCIe Card)HW Config > PC Station > CP 1623Time-of-Day TabIn SIMATIC mode (As Receiver)Station Config EditorWindows Taskbar > Station ConfigComponent StateStatus: RUN, Mode: ConfiguredWinCC OS ExplorerWinCC Explorer > Time SynchronizationPlant Bus Access PointCP1623(ISO)Time FormatPlant-Wide StandardSystem Time FormatUTC (Coordinated Universal Time)

Verification

To confirm that the CP 1623 is properly synchronized to the CPU 410-5H:
1. In the Windows Control Panel, open Set PG/PC Interface.
2. Select CP1623(ISO) and click Diagnostics > Read Station Time.
3. Verify that the displayed station time matches the CPU 410-5H internal clock within +/- 1 millisecond.
4. In WinCC Explorer, open the Time Synchronization editor: verify that the diagnostic status box displays 'Time synchronization active - Synchronized to Master'.
5. In the WinCC Alarm Logging runtime banner, verify that new alarms display continuous, synchronized timestamps without warning flags.

Limitations and Operational Precautions

When configuring time synchronization on the plant bus:
1. Never Configure Multiple Masters on the Same Bus: Operating more than one SIMATIC Time Master on the same physical Industrial Ethernet subnet causes clock collisions (jitter and oscillating time corrections). Ensure only one CPU 410-5H or SICLOCK master acts as Master.
2. UTC Mandate: Both the CPU and CP 1623 must operate strictly in UTC. Local time offsets should only be applied at the WinCC HMI presentation layer.
3. Network Switch Filtering: Verify that managed Ethernet switches (SCALANCE X-200 / X-300) between the CPU and OS station do not filter or block Layer-2 SNAP broadcast frames (MAC address 09-00-06-01-00-01).

Engineer FAQ

Why did the warning disappear after downloading the OS HW Config?

Because downloading HW Config transmitted the required system data blocks (SDBs) to the CP 1623 communications processor, enabling its internal firmware clock receiver.

Can CP 1623 synchronize via NTP instead of SIMATIC mode?

Yes. CP 1623 supports NTP. However, for high-precision Sequence of Events (SOE) timestamping within 1 ms, Siemens mandates SIMATIC mode broadcast synchronization over the Industrial Ethernet plant bus.

What happens if the Time Master CPU is powered down?

If the primary master drops, the CP 1623 continues running on its high-stability internal crystal oscillator with minimal drift until the standby CPU 410-5H assumes the master role.

Can standard Intel network cards (IE General) achieve 1 ms time synchronization?

No. Standard commercial NICs do not have onboard coprocessors to parse hardware timestamps at the physical Layer 2 frame boundary. Precision 1 ms SOE requires CP 1623 or CP 1613.