Cross-System Plant Integration: Bridging Diverse SIMATIC PCS 7 Versions (V7.1 and V8.0)

Direct OS server package cross-loading between PCS 7 V7.1 and V8.0 is unsupported due to incompatible WinCC database schemas and APL faceplate structures. To monitor and control process equipment across systems, implement hardware PN/PN Couplers for deterministic, galvanically isolated data exchange, configure S7-Communication with BSEND/BRECV blocks over an IP router, or install referenced multi-client stations.

Architectural Challenges Across Version Boundaries

Industrial facility expansions frequently require integrating an existing legacy system (e.g., PCS 7 V7.1 SP4 with CPU 417-5H and redundant WinCC V7.0 SP3 servers on subnet 192.168.0.x) with a new plant section (e.g., PCS 7 V8.0 SP2 with CPU 410-5H and redundant WinCC V7.2 servers on subnet 192.168.10.x). Plant operators require centralized visibility and supervisory control of motors, valves, and transmitters across both plant sections.

In homogeneous PCS 7 environments, multi-system integration is achieved by generating an OS Server Package on Server B and importing it into the WinCC project of Server A or a multi-client. However, cross-loading server packages between divergent major versions (V7.1 vs V8.0) fails because:
1. WinCC Database Schema Incompatibility: WinCC V7.0 SP3 uses Microsoft SQL Server 2005, whereas WinCC V7.2 utilizes Microsoft SQL Server 2008 R2 SP1. The underlying tag archiving, alarm logging, and C-scripting runtime engines cannot cross-reference remote packages across differing database versions.
2. APL Block Icon and Faceplate Structure Disparity: Advanced Process Library (APL) version 7.1 and version 8.0 utilize different structure definitions (STRUCT) for faceplate communication, internal state variables, and operator message authorization. Cross-version display generates graphical script errors and malformed faceplates.

Consequently, integration must occur either at the automation station (AS-to-AS) communication layer or through dedicated operator client bridging architectures.

Cross-System Integration Topologies

Engineers can deploy three distinct architectural patterns to bridge two heterogeneous PCS 7 systems:

1. Hardware Deterministic Coupling (PN/PN Coupler)

Mechanism: Deploy a Siemens PROFINET/PROFINET Coupler (e.g. 6ES7158-3AD10-0XA0). Each side of the coupler connects to the respective plant bus or PROFINET network of System 01 and System 02.
Benefits: Completely decouples the two networks physically and logically. No IP routing, subnet translation, or cross-system S7 connection licenses are required. Each CPU treats the coupler as local decentralized peripheral I/O (PIW/PQW).
Data Capacity: Supports up to 1440 bytes of input/output data exchange cyclically with microsecond update rates.

2. S7 Connection over Layer-3 Industrial Router (BSEND/BRECV or USEND/URECV)

Mechanism: Interconnect the plant bus networks via an industrial security router (e.g., SCALANCE S615 or SCALANCE XC-200 series). Configure an unspecified S7 Connection using ISO-on-TCP (RFC 1006) between the CPU 417-5H and CPU 410-5H.
Data Transfer:
Utilize BSEND (SFB12) and BRECV (SFB13) for block-oriented transmission of up to 64 Kbytes per telegram.
Alternatively, deploy PCS 7 standard communication blocks SEND_R / RCV_R (for Real values) and SEND_BO / RCV_BO (for Boolean status).
Control Philosophy: System 01 reads status signals (running, tripped, remote) and sends operator commands (start, stop, setpoint) to the controlling logic running in System 02.

3. Dedicated Operator Stations (Referenced / Dual-Screen Clients)

Mechanism: Deploy an engineering-approved multi-station console where an operator station physically houses two independent thin-client sessions (or adjacent monitors), one pointing to System 01 WinCC servers and the other connected to System 02 WinCC servers. Alternatively, deploy WinCC WebNavigator / WebUX sessions to view secondary system graphics securely.

Configuration and Implementation Guide

Implementing AS-to-AS S7 Communication via S7 Blocks

Configure S7 Connection in NetPro:
* Open NetPro in System 01. Insert an Unspecified S7 Connection pointing to the IP address of System 02's communication interface (CP 443-1 or CPU 410 onboard PROFINET port).
* Specify local TSAP (e.g., 10.03) and remote TSAP matching the CPU rack/slot.
* Repeat the mirror configuration in System 02's NetPro project.
Define Shared Data Structures:
* Create a global Send DB and Receive DB in both controllers.
* Structure data strictly by signals needed for visualization and control (e.g., Run_Fbk, Fault_Act, Man_Cmd, Auto_Cmd, SP_Ext).
* Avoid attempting to pass raw internal APL structures across systems, as internal structure offsets differ between APL V7.1 and V8.0.
Instantiate Transfer Blocks in CFC:
* Place BSEND in a cyclic interrupt chart (OB32/OB35) triggered on signal state changes or cyclic timers (e.g., 500 ms).
* Place BRECV in the corresponding partner chart, mapping output tags directly into the local visualization driver blocks.
Configure Local Mode on APL Blocks:
* For equipment controlled across systems, utilize the APL Local Mode feature (LocalSetting = 2 or LocalSetting = 4). This ensures operators on both systems receive visual feedback when an asset is under external or remote supervisory control.

Cross-System Integration Architecture Comparison

Integration ApproachProtocol / InterfaceMax Data ThroughputVersion DependencySubnet IsolationEngineering ComplexityPN/PN Coupler (6ES7158-3AD10-0XA0)PROFINET IO cyclic data1440 Bytes I/O per cycleFully independent (V5.x to V9.x+)Complete physical & logical galvanic isolationLow (standard HW Config module mapping)S7 Connection (BSEND / BRECV)ISO-on-TCP (RFC 1006) over IP RouterUp to 64 KB per block transferIndependent at application layerRequires IP routing or gateway across subnetsModerate (NetPro connection & CFC handshakes)Standard PCS 7 (SEND_R / RCV_R)S7 Communication (CFC Drivers)32 Real / 32 Bool per blockIdentical or compatible library blocksRequires flat network or routed plant busModerate (multiple block instances needed)OS Server Package SharingWinCC Proprietary RPC / SQLFull Tag Logging / Alarm ArchiveStrictly Incompatible across major versionsRequires shared Terminal Bus & DomainNot supported across V7.1 and V8.0

Verification

In NetPro on both systems, verify the configured unspecified S7 Connection shows Configured - Active.
Online in CFC on System 01, verify BRECV outputs DONE = 1 and ERROR = 0.
Invert a test digital input bit on System 02; observe state update in System 01 within one communication cycle (<500 ms).
Simulate an equipment trip in System 02; confirm the status alarm is generated and acknowledged on System 01 faceplates.
Sever the cross-system network cable; verify communication watchdog logic sets local control blocks to a defined safe state within 2 seconds.

Limitations and Operational Precautions

Communication Watchdog Mandate: Never link inter-controller interlocks across cross-system Ethernet links without heartbeat / watchdog verification. If communication is interrupted, the receiving system must freeze setpoints or force assets into safe state.
Safety Program Exclusion: Safety-related signals (SIL 2 / SIL 3) cannot be transferred via standard S7 connections or standard PN/PN Couplers. Safety interlocks require fail-safe S7 F-Connections over PROFIsafe.
Licensing and Distributor Notice: When sourcing industrial routers, communication processors (e.g. CP 443-1), or PN/PN Couplers (6ES7158-3AD10-0XA0), verify equipment specifications against current Siemens catalogs and validate order numbers with an authorized distributor.

Engineer FAQ

Can I migrate just one OS server to PCS 7 V8.0 to bridge the two systems?

No. OS servers and OS clients within an engineering multiproject must share the identical PCS 7 release and WinCC version. Running mixed WinCC versions in a single server pair or client-server domain causes database corruption.

How many SEND_R and RCV_R blocks can an S7-400H controller support?

An S7-400H CPU can manage hundreds of communication blocks, but performance is limited by the configured S7 Connection quota (typically 64 to 120 connections depending on CPU model) and communication load cycle allocation in HW Config.

Why is ISO transport protocol preferred over TCP/IP for S7 connections across subnets?

ISO transport operates using MAC addresses and does not require IP configuration. However, ISO transport cannot cross IP routers. If connecting across different subnets (192.168.0.x and 192.168.10.x), you must use ISO-on-TCP (RFC 1006) via an IP router.