Configuring SIMATIC CN 4100 Redundant Architecture and CNET Tool Workflow in SIMATIC PCS 7

In SIMATIC PCS 7 high-availability environments, redundant integration of third-party package units is achieved by pairing two SIMATIC CN 4100 communication nodes with fault-tolerant S7-400H or CPU 410-5H controllers. In CNET, both CN 4100 nodes are configured with synchronized Modbus/TCP or OPC UA connection sessions and redundant PROFINET IO device interfaces. S7-400H redundant driver blocks automatically arbitrate between the primary and standby CN 4100 modules, ensuring bumpless communication failover without process disruption.

Executive Summary

In critical industrial infrastructure (such as chemical reactors, offshore oil platforms, and pharmaceutical manufacturing), continuous communication with third-party package units is essential for plant safety and operational continuity. Deploying a single communication gateway introduces a single point of failure: an interface cable disconnection or hardware fault halts process data transfer and trips safety interlocks.

To achieve maximum availability, SIMATIC PCS 7 supports redundant SIMATIC CN 4100 configurations paired with fault-tolerant S7-400H or CPU 410-5H controllers. Operating in a hot-standby topology, both CN 4100 nodes maintain active communication sessions with the controller across redundant PROFINET rings while synchronizing field polling to external Modbus TCP or OPC UA servers. This technical guide outlines the redundant hardware architecture, CNET synchronization rules, and STEP 7 driver configuration required for seamless gateway redundancy.

Architecture and Fundamental Mechanics

The redundant CN 4100 architecture employs deterministic fault-tolerant synchronization across dual networks:

Dual-Sided Redundant Topology:
- Plant Bus Side: Both CN 4100 units connect to redundant PROFINET IO networks (MRP / MRPD rings) coupled directly to redundant CPU 410-5H controller interfaces.
- Field Side: Both CN 4100 units connect to redundant Ethernet field switches interfacing with the third-party package unit PLCs.
CNET Redundancy Configuration:
- In the CNET engineering tool, the nodes are paired as a redundant system (CN 4100 Redundant Pair).
- A dedicated inter-node synchronization link (or synchronization over the local management subnet) monitors health heartbeats between Master and Standby nodes.
- CNET generates identical register mapping dictionaries for both units, ensuring consistent symbol naming in STEP 7.
Controller Redundancy Arbitration:
- In the S7 controller, redundant driver blocks from the PCS 7 CN 4100 Library monitor the status of both nodes via PROFINET cyclic IO and diagnostic alarms.
- During normal operation, the Primary CN 4100 polls field devices and updates controller input images. The Standby CN 4100 maintains passive connection readiness.
- If the Primary node suffers a power loss, network fault, or field slave timeout, the driver block switches active data ingestion to the Standby CN 4100 within milliseconds, maintaining unbroken process control.

Step-by-Step Implementation Procedure

Follow these steps to configure a redundant SIMATIC CN 4100 architecture in PCS 7:

Physical Hardware and Network Cabling:
- Install two SIMATIC CN 4100 modules side-by-side on the DIN rail.
- Connect ports X1 and X2 of both modules to the redundant field switches.
- Connect ports X3 and X4 of both modules to the redundant PROFINET ring switches connecting to CPU 410-5H.
- Wire independent 24 V DC feeds from separate power supplies to each unit.
Configure Redundant Nodes in CNET:
- Open CNET and create a new project.
- Add two CN 4100 nodes and select the option 'Enable Hardware Redundancy'.
- Assign primary and secondary virtual IP addresses and define the heartbeat monitoring interval (recommended 100 ms).
- Configure Modbus TCP or OPC UA client connections: specify primary and backup IP addresses of the third-party slave devices.
- Define data mapping tables for process analog and binary signals.
Export System Data and Import to HW Config:
- In CNET, compile the redundant configuration and generate the STEP 7 integration package.
- In SIMATIC Manager HW Config, open the PROFINET IO system under CPU 410-5H.
- Insert the redundant CN 4100 GSDML objects onto the PROFINET IO system.
- Assign device names and IP addresses matching the CNET configuration.
Configure Redundant CFC Channel Drivers:
- Open the target CFC charts in SIMATIC Manager.
- Place redundant CN 4100 channel driver blocks from the library (e.g., CN_RedInReal, CN_RedInBool).
- Connect the block address inputs to the redundant symbolic I/O addresses defined in the symbol table.
Compile Charts and Download:
- Select 'Chart > Compile > Charts as Program...' with 'Generate module drivers' enabled.
- Download the user program to CPU 410-5H in RUN mode.
- In CNET, download the configuration files to both CN 4100 appliances.

Verification

Verify CNET online status: confirm both Primary and Standby CN 4100 nodes indicate 'Synchronized' and 'Healthy'.
Open CFC chart in Test Mode: verify that process signals display valid quality codes (16#80) and match field instruments.
Perform redundancy failover test: physically disconnect the field network cable from the Primary CN 4100.
Observe CPU diagnostic buffer and CFC driver blocks: confirm that the Standby CN 4100 assumes primary polling seamlessly without generating false bad-quality alarms on WinCC faceplates.
Reconnect the cable: verify that the system returns to normal dual-node redundancy.

Limitations and Operational Precautions

Third-party package unit PLCs must support concurrent TCP socket connections if both CN 4100 nodes maintain active sockets, or the package unit must support standard Modbus TCP connection failover. In PROFINET ring networks, verify that MRP (Media Redundancy Protocol) ring recovery times do not conflict with CN 4100 heartbeat watchdog timers. Hardware options and system licenses should be validated through an authorized Siemens distributor or the Siemens Industry Mall.

Engineer FAQ

Can two CN 4100 modules operate in hot-standby redundancy?

Yes, the SIMATIC CN 4100 natively supports redundant pairing when configured via CNET and integrated into PCS 7.

What happens during a field network cable failure on the primary CN 4100?

The redundant driver block detects the failure via PROFINET diagnostics and switches active data processing to the standby CN 4100 within milliseconds.