Configuring Redundant WinCC OS Communication with S7-300 Controllers in SIMATIC PCS 7

In SIMATIC PCS 7 systems operating with redundant OS Servers, integrating an S7-300 controller (such as CPU 315-2 PN/DP or via CP 343-1) using the SIMATIC PCS 7 Industry Library cannot utilize fault-tolerant 'Named Connections' during OS compilation. S7-300 hardware lacks the internal protocol multiplexing required for fault-tolerant Named Connections, which are exclusive to S7-400 and CPU 410 controllers. Communication between redundant OS Servers and S7-300 controllers must be established using standard Industrial Ethernet (TCP/IP) channels in the SIMATIC S7 Protocol Suite, where both redundant servers maintain independent TCP/IP connections to the S7-300.

Architectural Limits of S7-300 in SIMATIC PCS 7 Environments

While SIMATIC PCS 7 is primarily built around S7-400 and CPU 410 automation systems, packaged skid units, water treatment sub-systems, and third-party vendor packages often incorporate SIMATIC S7-300 controllers (e.g. CPU 315, CPU 317, or CPU 319).

To integrate these package units into the PCS 7 supervisory tier, Siemens provides the SIMATIC PCS 7 Industry Library (IL):
- Supplies S7-300 function blocks that emulate APL behavior, generating compatible WinCC structure tags, faceplates, and alarms.
- However, integrating S7-300 controllers into a high-availability PCS 7 environment requires observing foundational fieldbus communication constraints.

Why Named Connections Fail on S7-300 Hardware

When compiling an OS in SIMATIC Manager, the compiler prompts the engineer to select a connection type:
1. Named Connections:
- Relies on PC Station configuration components, the SIMATIC NET communication daemon, and hardware-level ISO transport protocols.
- Designed specifically for S7-400H / CPU 410-5H fault-tolerant communication, where a single symbolic logical connection name handles automatic bumpless failover between dual redundant network paths.
- S7-300 Incompatibility: S7-300 CPUs and CP 343-1 processors do not support S7 fault-tolerant connection endpoints or Named Connection routing tables in firmware. Attempting to force Named Connections on an S7-300 during OS compile results in communication failure (0xFFDF 410E or channel disconnected).

Configuring Redundant OS Communication via Industrial Ethernet (TCP/IP)

To achieve reliable communication between redundant OS Servers and an S7-300 PLC:

Configure S7 Connection in NetPro:
- In NetPro, establish an S7 Connection from OS Server 1 to the S7-300 CPU (via integrated PN port or CP 343-1).
- Establish an independent second S7 Connection from OS Server 2 to the same S7-300 CPU.
Select TCP/IP Connection in OS Compile Wizard:
- In the OS Compile wizard, under the Connection selection dialog, do NOT choose Named Connections.
- Select Industrial Ethernet (TCP/IP) under the SIMATIC S7 Protocol Suite.
Independent Runtime Polling:
- In WinCC Runtime, both OS Server Master and OS Server Standby maintain independent, simultaneous TCP/IP connections to the S7-300.
- If OS Server Master fails, OS Clients fail over to OS Server Standby, which is already polling the S7-300 across its own independent TCP/IP channel, providing seamless operator monitoring.

Connection Protocol Selection Matrix for PCS 7 Controllers

The following table details connection protocol compatibility across controller families in SIMATIC PCS 7:

Automation Controller ModelConnection Channel in WinCCFault-Tolerant Named Connection SupportHardware InterfaceRecommended ArchitectureCPU 410-5H Process AutomationNamed ConnectionsFully Supported (Bumpless)Integrated PN / CP 1623Standard PCS 7 Named ConnectionS7-400H Redundant PairNamed ConnectionsFully Supported (Hardnet / Softnet)CP 443-1 / CP 1623Standard PCS 7 Named ConnectionSingle S7-400 (e.g. CPU 416-3)Named Connections or TCP/IPSupported (Single channel)CP 443-1 or PN PortNamed Connection or TCP/IPS7-300 (CPU 315 / 317 / 319)Industrial Ethernet (TCP/IP)UnsupportedIntegrated PN or CP 343-1Dual independent TCP/IP connectionsWinAC RTX (PCS 7 Box)Named Connections or TCP/IPSupported (Single channel)Integrated PN / CP 1616Standard PC Station connection

Note: S7-300 integration via Industry Library requires procuring the PCS 7 Industry Library runtime license for S7-300 controllers.

Verification

Verify redundant OS communication with the S7-300 PLC:
1. Compile the OS project with the S7-300 connection mapped to Industrial Ethernet (TCP/IP).
2. Launch WinCC Runtime on both OS Server 1 and OS Server 2.
3. Open WinCC Channel Diagnosis on OS Server 1; verify that the connection to the S7-300 under TCP/IP displays status 'OK' with green checkmark.
4. Open WinCC Channel Diagnosis on OS Server 2; verify independent active connection status 'OK'.
5. Open an Industry Library motor or valve faceplate; verify that process values update smoothly and operator commands execute cleanly.

Limitations and Operational Precautions

Essential rules for S7-300 integration in PCS 7:
- The S7-300 controller has limited S7 communication resources (typically 16 to 32 concurrent connections); ensure connecting two OS servers and an ES does not exceed available connection resources.
- ALARM_8P chronological alarm messaging is supported on S7-300 only when utilizing the specific Industry Library blocks designed for S7-300.
- S7-300 controllers cannot participate in bumpless AS-to-AS communication via Named Connections; cross-communication with S7-400 requires S7 basic communication or Open User Communication.

Engineer FAQ

Can I use an S7-300 as a central controller in a large PCS 7 plant?

No. The S7-300 is only supported as a subsystem or package unit via the Industry Library; standard PCS 7 plant architectures mandate S7-400 or CPU 410 controllers.

Why did tags work on TCP/IP but fail on Named Connection?

Named Connections require S7-400 PC Station server support, which does not exist in S7-300 operating systems. TCP/IP uses standard RFC 1006 S7 communication supported by all S7 controllers.

Do I need CP cards in the OS servers to talk to S7-300 over TCP/IP?

No. Standard commercial Ethernet network cards (Softnet) on the OS servers can communicate with the S7-300 over standard TCP/IP without requiring specialized CP 1623 hardware.