C135 PCS 7 (PCS7)
6C
6 Cielo Ciencia y Tecnología
·Publicada en C135 PCS 7 (PCS7)

How to Configure Cross-Project S7 Communication Between S7-400 Automation Stations with Asymmetric CP 443-1 and Onboard PN Interfaces

How to Configure Cross-Project S7 Communication Between S7-400 Automation Stations with Asymmetric CP 443-1 and Onboard PN Interfaces

Configuring S7 communication between two SIMATIC S7-400 controllers located in separate PCS 7 multi-projects where one station utilizes an external CP 443-1 communications processor and the other utilizes the CPU integrated PROFINET (PN/IE) interface requires creating an 'Unspecified' S7 Connection in NetPro. Because the target station does not reside in the local multi-project database, engineers must manually configure the remote IP address, subnet mask, and TSAP coordinates (Rack and Slot) matching the partner CPU. If an asymmetric network configuration is applied or routing mismatched, communication watchdog faults or CPU maintenance requests will occur. Standard S7 communication blocks (BSEND/BRCV or USEND/URCV) handle bidirectional block data transmission across the connection ID.

Table of Contents

Network Architecture and Communication Interface Topology

In distributed industrial automation facilities running SIMATIC PCS 7, process units frequently operate under independent multi-projects. Interconnecting these autonomous stations for inter-plant interlocks or mass-balance tracking requires cross-project Industrial Ethernet communication.

A common engineering scenario involves asymmetric interface hardware:
* Automation Station A (AS-A): Equipped with an S7-400 CPU and a dedicated CP 443-1 communications processor (6GK7443-1EX30-0XE0), providing hardware-offloaded ISO-on-TCP and TCP/IP protocol processing.
* Automation Station B (AS-B): Modernized with a CPU featuring an integrated PROFINET interface (such as CPU 414-3 PN/DP, CPU 416-3 PN/DP, or CPU 410-5H), where Industrial Ethernet communication terminates directly on the CPU PN/IE ports.

When these stations reside in different PCS 7 multi-project databases, standard cross-project connection compilation via SIMATIC Manager cannot resolve partner hardware objects automatically. The connection must be defined manually as an Unspecified S7 Connection.

Configuring Unspecified S7 Connections in NetPro

To establish the communication channel from Station A to Station B:

  1. Open NetPro in Station A's Project:
    * Select CPU in Rack 0 (or the CPU owning the communication program).
    * In the lower connection table, double-click an empty row.
    * Connection Partner: Select Unspecified.
    * Type: Select S7 connection. Click OK.
  2. Configure General Connection Properties:
    * Under the Interface dropdown, select the local network adapter:
    • If originating from Station A, select the CP 443-1 (ISO-on-TCP or TCP/IP).
    • If originating from Station B, select the CPU PN-IO [IP-1] interface.
    • Enter the Remote IP Address matching the exact static IP assigned to the partner station's interface.
  3. Establish Active Connection Establishment:
    * Check the box: Active connection establishment on the initiating station.
    * The responding station must have this option unchecked if mirrored, or left passively listening for incoming TSAP requests.

TSAP Addressing Rules and Connection Table Mapping

S7 communication relies on Transport Service Access Points (TSAPs) to route packets through the backplane to the specific CPU operating system kernel.

For an Unspecified S7 Connection:
* Local TSAP: Automatically generated by NetPro (e.g., 10.02 indicating connection type 10 hex and CPU Rack 0, Slot 2/3/4).
* Remote TSAP: Must be configured manually by the engineer to match the physical hardware placement of the partner controller:
* First byte: Typically 03 or 10 (standard S7 connection).
* Second byte: Encodes Rack Number and Slot Number of the target CPU.
* Formula: TSAP Byte 2 = (Rack Number * 32) + Slot Number.
* Example: For a target CPU residing in Rack 0, Slot 3, the byte is (0 * 32) + 3 = 03 hex. For Rack 0, Slot 4, the byte is 04 hex.
* If communicating with a redundant S7-400H station, an unspecified connection terminates on one specific subsystem CPU; fault-tolerant redundant cross-project connections require S7-REDCONNECT or bilateral CP configurations with redundant IP pairings.

Data Exchange Programming via BSEND/BRCV and USEND/URCV

Once NetPro connection tables are saved and compiled, data exchange is programmed in Continuous Function Chart (CFC) or ladder logic using standard SIMATIC communication blocks from the standard library:

  1. BSEND (SFB12) and BRCV (SFB13) - Block-Oriented Reliable Transfer:
    * Best suited for deterministic transmission of data structures up to 64 KB.
    * Operates asynchronously with handshake acknowledgement: BSEND.REQ triggers transmission; BSEND.DONE confirms reception by partner; BRCV.NDR flags new data received.
    * Connection binding: Connect parameter ID to the connection ID (hexadecimal integer) assigned in NetPro. Set parameter R_ID (Range ID, DWORD) to match identically on both BSEND and BRCV instances.
  2. USEND (SFB8) and URCV (SFB9) - Uncoordinated Fast Transfer:
    * Transmits smaller data packets (up to 440 bytes) without receive confirmation handshaking.
    * High performance for continuous telemetry where occasional packet drop is tolerable.
  3. Buffer Management and Scan Rate:
    * Never execute BSEND on every CPU cycle. Trigger REQ on a periodic pulse (e.g., 500 ms clock memory) or upon data change detection (R_TRIG).

Comparison of Communication Configurations and Protocols

The table below compares network characteristics when configuring S7 communication across CP 443-1 versus CPU onboard PROFINET interfaces.

Parameter / FeatureCP 443-1 Processor LinkCPU Onboard PN/IE LinkCross-Project Unspecified S7 LinkBackplane Resource ImpactZero CPU protocol overhead; handled by CPCPU microprocessor executes communication stackDepends on physical port selectedProtocol SupportISO Transport, ISO-on-TCP (RFC 1006), TCP/IPISO-on-TCP (RFC 1006), TCP/IP, UDPISO-on-TCP or TCP/IP strictly requiredMaximum Data Block (BSEND)Up to 64 KB per transmissionUp to 64 KB per transmissionUp to 64 KB per transmissionConnection ID ManagementManaged locally in NetPro tableManaged locally in NetPro tableMust match local NetPro ID in CFC blockFault Tolerant (Redundant)Requires S7-REDCONNECT & 2x CPsRequires dual PN interfaces & H-CPUPassive single-point S7 connectionRouting Across SubnetsSupported via IP Gateway parameterSupported via IP Gateway parameterGateway required if subnets differ

Verification

To confirm that cross-project S7 communication is operational:
1. In NetPro, download the connection tables to both controllers: PLC > Download > Selected Stations.
2. Select CPU and open PLC > Diagnostics/Setting > Connection Status. Confirm the Unspecified S7 Connection state reports Established (green checkmark).
3. Open the CFC chart containing BSEND and BRCV.
4. Switch CFC to Test Mode: verify that BSEND.ERROR is FALSE, BSEND.STATUS displays 16#0000, and BSEND.DONE toggles periodically.
5. On the partner station, verify that BRCV.NDR pulses TRUE and the destination data block receives updated process values matching the source buffer.

Limitations and Operational Precautions

  • Unspecified S7 connections lack automatic consistency checking; if the partner station's IP address or CPU slot number changes, the connection will drop without warning in NetPro.
  • A single CP 443-1 or CPU onboard port cannot maintain an S7-400H fault-tolerant redundant connection; if a cable or CPU fails, communication halts until manual failover occurs.
  • Do not configure multiple BSEND blocks with the identical ID and R_ID combination targeting the same connection, as internal buffer collisions will abort transmission.
  • Verify that hardware equipment schedules and software licensing align with the applicable Siemens catalog and authorized distributor quotation.

Engineer FAQ

Can two S7-400H redundant systems communicate across different projects?

Yes, but an Unspecified S7 Connection only connects to one specific CPU/rack. To achieve true fault tolerance across different projects, both projects must configure bilateral connections using S7-REDCONNECT, or merge both AS stations into a single multi-project to compile native fault-tolerant S7 connections.

What causes error 16#0001 or 16#0014 on BSEND?

16#0001 indicates a communication error (connection not established or partner unreachable). 16#0014 indicates that the specified connection ID does not exist in the local CPU connection database.

Why does the CPU enter Maintenance Demanded when configuring an S7 connection?

Maintenance Demanded occurs if the connection properties specify an interface subnet that does not match the actual IP address or subnet mask assigned in HW Config, or if duplicate IP addresses exist on the physical industrial switch.

Technical References

Related Articles

Related Tags

  • S7 Communication
  • CP 443-1
  • NetPro
  • BSEND
  • S7-400
6 respuestas