Configuring Network Time Protocol (NTP) and SIMATIC Time Synchronization on CPU 410-5H

On SIMATIC PCS 7 CPU 410-5H controllers, clock synchronization via onboard PROFINET interfaces (PN-IO-X5) must be configured using Network Time Protocol (NTP) rather than ISO SIMATIC mode. Unlike CP 443-1 communication processors, the onboard PROFINET interfaces of CPU 410-5H operate purely on Ethernet TCP/IP and do not support user-defined MAC address assignment for ISO layer 2 SIMATIC time broadcasts. To achieve plant-wide sub-second time stamping, configure the CPU PN-IO-X5 interface as an NTP Client pointing to the IP addresses of the redundant OS Servers or a central SICLOCK master, set the update interval (typically 10 seconds), and configure CPU Diagnostics/Clock properties as 'In the PLC: As Slave'.

Time Synchronization Architecture: NTP vs SIMATIC Mode

In a distributed control system, uniform system time across all automation stations (AS), operator stations (OS), and distributed I/O racks is mandatory to correlate alarms, chronological event logs, and sequence-of-events (SoE) records during plant upsets. SIMATIC PCS 7 supports two primary time synchronization protocols:

Synchronization ProtocolUnderlying Network LayerAddressing MechanismSupported Hardware ModulesTypical AccuracySIMATIC ModeISO Layer 2 (MAC broadcast)Proprietary Ethernet multicast framesDedicated CP 443-1 communication processors$\pm 10\text{ ms}$Network Time Protocol (NTP)IP Layer 3 / UDP (Port 123)Unicast / Multicast IP addressingCPU 410-5H onboard PN-IO, CP 443-1, SCALANCE switches$\pm 1\text{ ms}$ to $\pm 10\text{ ms}$

While classic S7-400 systems equipped with CP 443-1 processors frequently used SIMATIC Mode via MAC addresses across the Plant Bus, modern architectures built around the CPU 410-5H standardize entirely on NTP.

Why CPU 410-5H Onboard PROFINET Interfaces Require NTP

The SIMATIC PCS 7 CPU 410-5H features integrated 2-port PROFINET interfaces (PN-IO-X5 and PN-IO-X8). Engineers migrating from CP 443-1 setups often attempt to configure 'SIMATIC Mode' on these onboard ports and discover that the configuration dialog blocks MAC address entry or fails to synchronize.

This behavior is governed by specific hardware architecture rules:

Fixed Hardware MAC Address: Onboard PROFINET interfaces on CPU 410-5H possess factory-burned physical MAC addresses that cannot be altered or assigned custom virtual MACs in HW Config.
Protocol Stack Separation: The onboard PROFINET controller stack is optimized for PROFINET IO real-time (RT) and isochronous real-time (IRT) traffic alongside TCP/IP communication. It does not implement the legacy Siemens ISO Industrial Ethernet transport stack required for SIMATIC Mode MAC broadcasts.
NTP Client Native Engine: The CPU 410 operating system includes an integrated NTP client engine capable of polling up to four independent NTP time servers cyclically, ensuring high availability even if an NTP server node fails.

Step-by-Step Configuration Workflow for CPU 410-5H and OS Servers

To configure reliable NTP time synchronization between redundant OS Servers and CPU 410-5H controllers, execute the following technical steps:

Configure OS Servers as NTP Time Masters: On the redundant OS Servers, configure the WinCC Time Synchronization editor (Time Sync in WinCC Explorer). Enable 'Synchronization via Terminal Bus' and select 'Make this computer the time master'. Ensure the Windows Time service (w32time) or Siemens NTP service is running.
Configure CPU Internal Clock Properties: In HW Config, double-click the CPU 410-5H central processing unit. Navigate to the Diagnostics/Clock tab. Under Clock, configure:
- In the PLC: As Slave
- On the AS-wide bus: None (or As Slave if bridging subnets)
Configure NTP Synchronization on PN-IO Interface: In HW Config, double-click the onboard interface PN-IO-X5 (or the specific port connected to the Plant Bus). Navigate to the Time-of-Day Synchronization tab:
- Check the box 'Enable NTP time-of-day synchronization'.
- Enter the IP addresses of NTP Server 1 (Master OS Server IP) and NTP Server 2 (Standby OS Server IP).
- Set the update interval to 10 seconds (recommended standard for DCS operation).
Compile and Download Hardware Configuration: Save and compile HW Config. Download the configuration to the AS controller (PLC -> Download to Current Project -> Selected Station).
Download NetPro Configuration: Open NetPro, execute Save and Compile, and download network parameters to ensure all routing and communication endpoints are synchronized.

Verification

Verify that the CPU 410-5H synchronizes its internal real-time clock with the NTP master through these diagnostic checks:

CPU Module Information Clock Status: In SIMATIC Manager, select the CPU 410-5H and open PLC -> Module Information -> Time System. Verify that the clock status displays Synchronized with the accurate UTC timestamp and that the last synchronization telegram timestamp updates every 10 seconds.
Diagnostic Buffer Inspection: Check the CPU diagnostic buffer (Module Information -> Diagnostic Buffer). Confirm that events log clean entries such as 'Time-of-day synchronization: Time telegram received' and that zero time synchronization error records appear.
WinCC Tag Diagnostics: In WinCC OS Runtime, monitor internal system tags @TimeSyncState and @TimeSyncError. Confirm that @TimeSyncError reads 0 (No Error) and @TimeSyncState confirms Master/Standby synchronization.

Limitations and Operational Precautions

When implementing NTP time synchronization on CPU 410-5H, observe these network and configuration safeguards:

UTC Time Base Mandatory: In SIMATIC PCS 7, the controller operating system and Plant Bus time must strictly operate on Coordinated Universal Time (UTC). Never configure local time with daylight saving time offsets on the AS CPU; local time offsets are handled strictly by the WinCC OS display clients.
Firewall Port Availability: Ensure that industrial network switches, firewalls, and security appliances between the OS Servers and CPU 410-5H permit bidirectional UDP port 123 traffic.
Dedicated Master Clock for Sub-millisecond SoE: For high-precision Sequence of Events (1 ms SoE) across multiple controllers, deploy a dedicated GPS/GLONASS central time transmitter (such as Siemens SICLOCK TC 400 / SICLOCK TS) as the primary NTP stratum-1 server rather than relying solely on OS Server software clocks.

Engineer FAQ

Why can I not set a user-defined MAC address on PN-IO-X5 of CPU 410-5H?

The onboard PROFINET interfaces of CPU 410-5H utilize integrated hardware MAC addresses assigned during factory manufacturing. Unlike modular CP 443-1 cards, virtual MAC re-assignment is not supported by the CPU 410 hardware design.

What happens if both configured NTP servers become unreachable?

The CPU 410-5H internal quartz clock continues running autonomously with high stability ($\pm 2\text{ s/day}$). Once NTP servers reappear on the network, the CPU smoothly slews its clock back into synchronization without abrupt backward time jumps.

How does redundant CPU 410-5H synchronize time between the master and reserve CPUs?

In an AS 410-5H redundant pair, both CPUs receive NTP telegrams independently across their respective PN-IO interfaces, and the high-speed optical fiber synchronization links continuously harmonize clock cycles between the master and standby processors.