C135 PCS 7 (PCS7)
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Configuring SIMATIC PCS 7 Time Synchronization on Single Stations and Referenced OS Architectures

Configuring SIMATIC PCS 7 Time Synchronization on Single Stations and Referenced OS Architectures

To configure system-wide time synchronization in SIMATIC PCS 7 for an architecture consisting of an OS Single Station (OS1) and multiple Referenced OS stations (OS2-OS4) connected exclusively via the Plant Bus without a Terminal Bus, designate OS1 as the Time Master in WinCC Time Synchronization. Open the Time Synchronization editor in the WinCC project, select 'Synchronization via System Bus (Master, Slave)', set the mode to Master, choose the Plant Bus network interface, and check 'Display symbolic names of access points' for portability across referenced stations. In HW Config, configure all S7-400 CPUs as Time Slaves (Diagnostics/Clock), and in CP 443-1 properties, enable 'Forward time of day (SIMATIC mode)'.

Table of Contents

Executive Summary

Accurate time synchronization across industrial control systems is essential for millisecond-level chronological alarm logging, sequence-of-events (SOE) tracking, and historical trend alignment. In large multi-tier SIMATIC PCS 7 architectures, a central GPS/NTP clock (such as SICLOCK) typically synchronizes OS Servers via the Terminal Bus, while servers broadcast time to AS controllers over the Plant Bus. However, in smaller plant installations featuring multiple independent Single Stations or Referenced OS stations connected exclusively to a common Industrial Ethernet Plant Bus without a separate Terminal Bus, engineers frequently face challenges configuring the primary OS PC's local clock to act as the master time source for all CPUs and peer stations. This technical guide outlines the configuration of WinCC SIMATIC mode time broadcasting over the Plant Bus.

PCS 7 Time Synchronization Principles: Plant Bus vs Terminal Bus

PCS 7 supports two primary time synchronization protocols:

  • SIMATIC Mode (Layer 2 Ethernet Broadcast): Operates on the Industrial Ethernet Plant Bus via ISO transport frames (MAC-level broadcasts). Highly accurate and deterministic; supported natively by S7-400 CP 443-1 processors.
  • NTP Mode (Network Time Protocol): Operates on standard TCP/IP networks via UDP port 123. Used primarily on Terminal Buses and routed networks.

Referenced OS Stations: Shared Configuration and Master Negotiation

A Referenced OS shares the physical WinCC project database of a master OS (OS1) to minimize engineering effort across identical operator stations:

  • Because all referenced OS stations execute the identical project configuration, all are configured with the same Time Synchronization settings.
  • At runtime, WinCC negotiates mastership dynamically: The primary station (OS1) becomes 'Time Master Active', broadcasting clock telegrams.
  • Referenced peers (OS2, OS3, OS4) detect the active master and automatically transition to 'Time Master Standby', synchronizing their local Windows clocks to the active master.

S7-400 CPU and CP 443-1 Clock Synchronization Modes

For controllers to synchronize with the WinCC Time Master:

  • Industrial Ethernet CP (CP 443-1): Must have 'Activate time-of-day synchronization' enabled with 'SIMATIC mode' and 'Forward time of day' checked.
  • S7-400 CPU: In HW Config CPU properties under the Diagnostics/Clock tab, synchronization on the internal backplane bus (K-Bus / MPI) must be set to 'As Slave' with a synchronization interval of 1 to 10 seconds.

Time Synchronization Architecture Comparison

The following table compares time synchronization topologies across PCS 7 architectures:

Synchronization TopologyMaster Clock SourceProtocol UsedBus Infrastructure RequiredTypical AccuracyPlant Bus SIMATIC ModeWinCC Single Station (OS1)ISO Layer 2 BroadcastPlant Bus Only (No Terminal Bus)1 to 10 msSICLOCK GPS CentralHardware GPS Time MasterSIMATIC / NTPDedicated Terminal & Plant Bus< 1 ms (SOE Capable)NTP Client-ServerOS Server / Domain ControllerRFC 1305 NTPTerminal Bus (UDP 123)10 to 50 msCPU Internal MasterS7-400 CPU Real-Time ClockSIMATIC ModePlant Bus10 to 50 ms (Subject to drift)

Step-by-Step Procedure to Configure Time Sync via Plant Bus

Method 1: Configuring WinCC Time Synchronization Editor

  1. In SIMATIC Manager, open the OS1 project in WinCC Explorer.
  2. In the navigation tree, open the Time Synchronization editor.
  3. Check the box Synchronization via System Bus (Master, Slave).
  4. Select the radio button Master.
  5. Select the network card (access point) connected to the Plant Bus.
  6. Check Display symbolic names of access points so the configuration binds portably across referenced stations.
  7. If synchronizing the PC to an external Windows time service, check Access time from a specific computer; otherwise, leave unchecked to use OS1 PC time.
  8. Click OK and close the editor.

Method 2: Configuring S7-400 CPU and CP 443-1 in HW Config

  1. Open HW Config for each S7-400 controller.
  2. Double-click the CP 443-1 communications processor to open its properties.
  3. Switch to the Time-of-Day Synchronization tab.
  4. Check Activate time-of-day synchronization.
  5. Select SIMATIC mode and check Forward time of day.
  6. Double-click the S7-400 CPU object to open its properties.
  7. Switch to the Diagnostics/Clock tab.
  8. Under Synchronization in the AS, set mode to As Slave.
  9. Set the synchronization interval to 10 seconds.
  10. Execute Station > Save and Compile and download HW Config to the CPU.

Verification

To verify system-wide time synchronization:

  1. WinCC Status Check: In WinCC Runtime, open the Time Synchronization status window or APDIAG. Verify that OS1 reports 'Time Master Active' and OS2-OS4 report 'Time Master Standby'.
  2. Controller Clock Inspection: In SIMATIC Manager, select the CPU and execute PLC > Set Time of Day. Confirm that the CPU module time matches the OS1 PC time to the second.
  3. Alarm Timestamp Audit: Trigger a process digital input. Confirm that the WinCC alarm control displays the exact second of actuation matching the controller event.

Limitations and Operational Precautions

  • PC Clock Drift: Standard PC crystal oscillators drift by several seconds per week; for mission-critical audit trails, synchronize the OS1 PC to a secure NTP time server or external GPS receiver.
  • Dual Master Conflict: Never configure both the S7-400 CPU and WinCC OS as SIMATIC mode masters simultaneously; competing time broadcasts create severe clock jitter and duplicate alarm entries.
  • Daylight Saving Time (DST): SIMATIC mode broadcasts UTC time; ensure all OS stations are configured with the identical Windows timezone offset to prevent one-hour graphic display offsets.

Engineer FAQ

Can referenced OS stations become active time masters if OS1 is powered down?

Yes, referenced stations negotiate mastership dynamically; if OS1 goes offline, another referenced station assumes the active master role.

Why must 'Forward time of day' be enabled on the CP 443-1?

The CP receives time frames from Ethernet; 'Forward time' passes the synchronization telegram across the backplane bus to the CPU.

Does SIMATIC mode time synchronization work across standard corporate routers?

No. SIMATIC mode uses Layer 2 ISO multicast frames (MAC broadcasts) that are not routed across Layer 3 IP subnets.

Technical References

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