SICLOCK TC100 vs TC400 Configuring NTP and GPS Time Sync

Overview: Time Synchronization in S7-400 Industrial Ethernet Networks

Distributed SIMATIC S7-400 systems must share a single, accurate time base for sequence-of-events recording, batch report timestamps, shift logging, audit trails, OPC UA server timestamps, and energy-data correlation. Each S7-400 CPU (CPU 412, 414, 416, 417) maintains an internal 64-bit real-time clock with a 1 ms resolution, but the internal RTC drifts on the order of seconds per day and cannot be guaranteed coherent across 10–20 PLCs without an external reference. A GPS- or DCF77-disciplined Siemens SICLOCK time server delivers a single time-of-day reference, distributing it to every S7-400 over the plant Industrial Ethernet using the NTP/SNTP or SIMATIC TIME protocol.

This reference covers selection between the SICLOCK TC100 and SICLOCK TC400, antenna and receiver integration, CP 443-1 NTP client configuration in STEP 7 V5.x, SIMATIC TIME configuration, redundant operation, and field-proven diagnostic checks for a typical 15-PLC, 2-server, 10-client architecture.

Prerequisites

Before commissioning the time-of-day distribution, verify the following items are present and document their firmware versions:

• SICLOCK TC100 (6MF1110-0AA00) or SICLOCK TC400 (6MF1110-1AA00) time server with the latest firmware (V3.x as of 2024). Confirm on the Siemens support portal (support.industry.siemens.com) using the article search keyword SICLOCK.
• GPS receiver module for outdoor antenna, or DCF77 receiver for the Central European transmitter, depending on accuracy and infrastructure.
• CP 443-1 (6GK7443-1EX30-0XE0) or CP 443-1 Advanced (6GK7443-1GX30-0XE0) in every S7-400 station requiring synchronised time. The Advanced variant supports NTP/SNTP with a 1 ms-class sync interval.
• STEP 7 V5.5 SP4+ or STEP 7 Professional (TIA Portal) V15.1+ for HW Config and NetPro, plus NCM S7 Industrial Ethernet diagnostics.
• SIMATIC NET Industrial Ethernet with managed switches supporting IGMP snooping if SIMATIC TIME multicast is used. NTP/SNTP unicast only requires a standard Layer-2 switch.
• Plant firewall must permit UDP port 123 (NTP) between SICLOCK and each S7-400 station.

SICLOCK Product Family: TC100 vs TC400

Both devices are rack- or DIN-rail mounted time servers in the SIMATIC NET family. They share the same web configuration interface and the same NTP/SNTP server firmware, but differ in interface density, holdover performance, and redundancy options.

For a 15-station S7-400 cluster with two OPC servers and ten HMI clients (≈ 27 NTP clients), the TC100 has ample headroom. The TC400 is justified when the plant also feeds Ethernet-attached analysers, video, or third-party controllers from the same time reference, or when hot-standby redundancy of the time server itself is required.

Network Architecture for Distributed S7-400 Time Sync

All S7-400 stations and the OPC server sit on a single IE subnet (VLAN 100). The SICLOCK acts as the stratum-1 NTP source. The 15 PLCs each poll the TC100 every 10–60 s, the two OPC servers poll every 1 s for OPC UA server-timestamp accuracy, and the HMI clients poll every 60 s.

Selecting Between TC100 and TC400

Use the TC100 when:

• The total NTP client count is below ~500.
• Single time source is acceptable; brief GPS outages (≤ 1 hour) are tolerated with holdover to ±1 s.
• Cost is constrained and the application uses SIMATIC TIME on the IE subnet, not a cross-plant WAN.

Use the TC400 when:

• More than 500 NTP clients, or several thousand SIMATIC TIME receivers across multiple subnets.
• Hot-standby time-server redundancy is a contractual requirement (e.g. IEC 61850 substations, pharma, TÜV-audited plants).
• Future migration to S7-1500 + CP 1543-1 PTP is planned; the TC400 can be upgraded with a PTP grand-master firmware option.
• Holdover must stay within ±100 ms for more than 24 h (OCXO-disciplined).

S7-400 NTP Client Configuration on the CP 443-1

The S7-400 CPU itself does not speak NTP. Time-of-day synchronisation is delegated to the CP 443-1 in slot 4 (or any free slot). The CP then writes the received UTC into the CPU's date/time clock via the backplane at the configured interval.

Step-by-step (STEP 7 V5.x)

1. Open the S7 project in SIMATIC Manager and select the target station.
2. Open HW Config, double-click the CP 443-1, and switch to the Time-of-Day Synchronisation tab.
3. Tick Accept time-of-day on the S7-CPU from the LAN and select NTP mode.
4. Enter the SICLOCK IPv4 address, e.g. 192.168.100.10, and set the synchronisation interval to 10 s for the OPC server, 60 s for PLCs and HMIs.
5. Set the time zone to UTC on the CP; the CPU can be configured separately to local time using SFC 0 / SFC 1 in OB 1.
6. Compile and download. The CP 443-1 does not require a restart; NTP polling starts on the next KeepAlive cycle.

Sample SFC 1 (READ_CLK) call in OB 1 to read the synchronised clock into a DB for diagnostics:

// OB1 - read CPU time-of-day after CP-driven NTP sync
CALL  "READ_CLK"            // SFC 1
     RET_VAL := MW 100      // returns 0 on success
     CDT     := DB100.DBD0  // 8-byte DATE_AND_TIME buffer

// Push 8-byte buffer to display in HMI
CALL  "DT_TO_TOD"           // IEC FC
     IN  := DB100.DBD0
     OUT := DB100.DBD0      // TOD only (4 bytes)

To verify the CP 443-1 is actually receiving NTP frames, open NCM S7 Industrial Ethernet Diagnostics → station → Time-of-Day tab. The last accepted time, stratum, and offset in ms are displayed.

SICLOCK Hardware Installation

TC100 power and grounding

• Supply: 24 V DC ±20 %, max 0.5 A, connect to a clean UPS-backed 24 V bus.
• Functional earth (FE) terminal must be bonded to the cabinet PE bar with < 1 Ω impedance to keep surge protection of the antenna input effective.
• Mount on 35 mm DIN rail with at least 30 mm clearance above and below for convection.

GPS antenna

• Antenna type: active GPS L1, 3.3 V or 5 V supply from the receiver, gain ≥ 26 dB.
• Coaxial cable: RG-58 up to 15 m, RG-213 or Heliax LDF4-50A for longer runs. Max 60 m total cable loss < 12 dB.
• Sky view: 360° hemisphere with a 15° elevation mask. Avoid mounting next to large steel structures, VFDs, or soft-starter cabinets.
• Lightning protection: install a coaxial surge arrester (e.g. DEHNgate DGA AG BNC) at the building entry point and bond its earth to the plant ground bar.

DCF77 alternative

If the plant is in Central Europe and GPS is not permitted, the DCF77 receiver (e.g. SICLOCK DCF77 receiver) can be wired to the same antenna input. Accuracy: ±20 ms typical, no satellite dependency, but reduced to short-range coverage of the Frankfurt transmitter.

SICLOCK Web Configuration

After connecting a service laptop to port X1 and pointing a browser to https://192.168.100.10 (default IP, user admin, password on the device label), complete the following:

1. Status → GPS: confirm Satellites tracked ≥ 6, Position fix 3D, PDOP < 4. First cold start can take 12–20 minutes.
2. Configuration → Time source: select GPS (or DCF77) and set the local time-zone offset to UTC for downstream NTP — the NTP packet itself is always UTC.
3. Configuration → NTP:
   • Enable NTP server on each Ethernet port.
   • Set Stratum = 1 (advertises as primary reference when GPS is healthy).
   • Authentication: Symmetric key (MD5) recommended for S7-400; otherwise leave disabled for commissioning.
4. Configuration → SIMATIC TIME: enable master mode on the same VLAN, multicast group 224.0.1.1, send interval 1 s.
5. Configuration → Holdover: enter acceptable drift budget; the TC100 will downgrade its stratum and continue to serve NTP from the internal TCXO if GPS is lost.
6. Administration → Users: change the default admin password and create a read-only operator account for the maintenance team.
7. Click Save & Activate. The TC100 reboots in ~30 s and resumes NTP service.

SIMATIC TIME Configuration on the CP 443-1

SIMATIC TIME uses an Ethernet multicast frame (MAC 09-00-06-01-FF-EF, group 224.0.1.1). The CP 443-1 can accept either NTP or SIMATIC TIME on the same port. To switch the S7-400 station from NTP to SIMATIC TIME:

1. HW Config → CP 443-1 → Time-of-Day Synchronisation.
2. Change Mode from NTP to SIMATIC TIME.
3. Set Accept SIMATIC TIME from → LAN.
4. Download HW Config. The new configuration is active after the next CP 443-1 stop/start (toggle in NetPro or power-cycle the CP).

SIMATIC TIME advantages: lower CPU load on the CP 443-1 (no per-station polling), automatic IP-free reception (multicast), sub-millisecond jitter. Disadvantage: multicast must be allowed in the switching infrastructure; a single blocked IGMP querier on the IE subnet can stop SIMATIC TIME distribution silently.

Verification and Diagnostics

Once the SICLOCK is locked and the CPs are downloading, run the following verification matrix:

For field commissioning, the quickest end-to-end check is to load the SICLOCK web status page on a maintenance laptop, then watch the Offset graph of each CP 443-1. The trace should settle to a horizontal line within five poll intervals; any saw-tooth pattern indicates switch congestion or duplicate NTP servers polluting the client.

Redundancy and High Availability

Two SICLOCK TC400 units configured as a redundant pair deliver bumpless failover. The pair uses a dedicated sync cable (or the plant network) to elect a master and a standby. The standby continually updates its internal time from the master, so a takeover typically completes within 200 ms with no discontinuity in the served NTP stream.

For a TC100 deployment, redundancy is achieved at the NTP client side: each CP 443-1 can be configured with two NTP server addresses; if the primary fails to answer within four poll intervals, the CP switches to the secondary. Configure both 192.168.100.10 (primary TC100) and 192.168.100.11 (secondary TC100) in the CP. Note: a TC100 is a stratum-1 source, not a peer; running two TC100s side-by-side means each is independent and unsynchronised with the other unless they share a GPS reference. In that case they will both serve essentially the same UTC.

Troubleshooting Matrix

Cross-Reference: Other Vendor Time-Sync Approaches

For comparison, Allen-Bradley ControlLogix deployments can use the 1756-TIME module, which provides GPS-disciplined time and PTP (IEEE 1588) grand-master services on a ControlLogix chassis (see the 1756-TIME installation instructions, publication 1756-IN049B-EN-P). ProSoft Technology's Aparian Time Sync Module delivers similar PTP/NTP functionality for Logix racks without a dedicated GPS antenna at every chassis. Fluke's GPS430 is a portable accessory for synchronising Fluke 430 Series power-quality analysers. None of these substitute a SICLOCK on a Siemens-only S7-400 plant, but they are useful in mixed-vendor brownfield migrations where a common time reference must feed both Logix and SIMATIC sides.