C135 PCS 7 (PCS7)
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Understanding Named Connections vs S7ONLINE for Engineering Station Downloads in SIMATIC PCS 7

Understanding Named Connections vs S7ONLINE for Engineering Station Downloads in SIMATIC PCS 7

In SIMATIC PCS 7, engineers frequently confuse the communication pathways required for Engineering Station (ES) controller downloads with those required for Operator Station (OS) runtime visualization. S7 Named Connections configured in NetPro are strictly required for WinCC OS runtime tag polling and ES OS-Simulation; they are NOT required for downloading hardware configurations or CFC logic from the ES to the S7-400 CPU. Controller downloads from an ES utilize the standard 'S7ONLINE' access point routed through the physical network interface card (or 'PC internal.local.1') via standard Layer 4 ISO-on-TCP or ISO protocols, without requiring NetPro connection table definitions.

Table of Contents

Demystifying ES Communication Pathways: Downloads vs OS Simulation

A pervasive misconception in SIMATIC PCS 7 engineering is that an S7-400 controller cannot be downloaded unless an S7 Connection (Named Connection) is explicitly configured in NetPro between the Engineering Station (ES) and the CPU.

This misconception leads engineers to insert multiple PC Stations for the ES into different sub-projects, attempting to download NetPro connection tables to the local Station Configuration Editor and encountering configuration overwrite errors.

To understand the architecture:
- CFC / HW Config Downloads: Use the classic STEP 7 PG/PC Communication Channel operating via the S7ONLINE access point. It communicates directly with the CPU's IP address or MAC address across Layer 2/Layer 4 without pre-configured NetPro connection tables.
- WinCC OS Runtime / OS Simulation: Uses the SIMATIC NET Named Connections Channel. This strictly requires an S7 connection compiled in NetPro and loaded into the local Station Configuration Editor virtual rack.

The Role of S7ONLINE and 'PC internal.local.1'

In SIMATIC PCS 7:
- The PG/PC Interface on the Engineering Station is set to:
S7ONLINE -> PC internal.local.1.
- PC internal.local.1 directs all communication requests from SIMATIC Manager, CFC, and HW Config into the local Station Configuration Editor.
- The Station Configuration Editor maps these requests directly to the physical network card (IE General or CP 1623) assigned in HW Config.
- When an engineer clicks Download in CFC, STEP 7 queries the target CPU's configured IP address and executes the download directly. Zero NetPro S7 connection entries are referenced.

When Are NetPro S7 Named Connections Actually Required?

Configuring an S7 Connection between an ES and an AS in NetPro is required only if the engineer intends to execute WinCC OS Simulation on the Engineering Station:
- When testing graphic faceplates and alarms on the ES before commissioning on site, the local WinCC runtime must impersonate an OS Server.
- To read tags from the physical controller or S7-PLCSIM via Named Connections, NetPro requires an S7 connection between WinCC Appl. on the ES and the CPU.
- If the ES is strictly used for logic authoring, hardware compilation, and program downloads, no ES-to-AS connection in NetPro is ever needed.

Configuring a Single ES Across Multiple Multiprojects

When a customer maintains two separate multiprojects (e.g., Multiproject A and Multiproject B) managed from a single central Engineering Station:
- The Station Configuration Editor on the ES can hold only one active station configuration at any given moment.
- If NetPro is downloaded from Multiproject A, it overwrites the station configuration previously loaded from Multiproject B.
- Recommended Architectural Solution: Merge the two projects into a single unified PCS 7 Multiproject.
- In SIMATIC Manager, select File > Multiproject > Insert Project....
- Merge the plant bus subnets via Multiproject properties.
- This allows a single, unified NetPro view where the ES can download to all AS controllers seamlessly without configuration conflicts.

Comparative Communication Channel Matrix in PCS 7

The table below clarifies the communication mechanisms used by engineering tools:

OperationAccess Point UsedNetPro S7 Conn Required?Station Configurator ComponentHW Config Download to ASS7ONLINENo (Direct IP / MAC)Network Adapter (IE General / CP 1623)CFC / SFC Logic DownloadS7ONLINENo (Direct IP / MAC)Network AdapterAS Diagnostic Buffer CheckS7ONLINENoNetwork AdapterOS Simulation on ESNamed ConnectionsYes (S7 Connection)WinCC Appl. + Network AdapterOS Server Tag PollingNamed ConnectionsYes (S7 Connection)WinCC Appl. on OS Server

Step-by-Step Procedure: Configuring ES for Multi-AS Downloads

To configure a single ES to download to multiple controllers across projects:

Step 1: Configure Physical Network Adapter in HW Config

  1. In SIMATIC Manager, open HW Config for the ES PC station.
  2. Insert an IE General (or CP 1623) in Slot 2.
  3. Assign the static IP address and subnet mask of the ES plant bus interface.
  4. Save and compile HW Config.

Step 2: Configure Station Configuration Editor on ES

  1. Open Station Configuration Editor on the ES desktop.
  2. Ensure Slot 2 contains the network card matching HW Config.
  3. In SIMATIC Manager, right-click the ES station and select PLC > Configure..., followed by PLC > Download.
  4. The station manager displays the Yellow Pencil icon confirming successful binding.

Step 3: Set PG/PC Interface to PC Internal

  1. Open Windows Control Panel > Set PG/PC Interface.
  2. Select Access Point: S7ONLINE (STEP 7).
  3. Parameter assignment: PC internal.local.1. Click OK.

Step 4: Execute Controller Downloads

  1. Open any AS project within the Multiproject.
  2. Select the CPU and click PLC > Download.
  3. STEP 7 routes the download through PC internal.local.1 to the physical NIC, programming the CPU directly without NetPro connection definitions.

Verification

To confirm that ES downloads operate correctly across multiple controllers:
1. Station Configurator Status: Confirm that the Station Configuration Editor displays status RUN with a yellow pencil icon on the network card.
2. Accessible Nodes Audit: In SIMATIC Manager, click PLC > Display Accessible Nodes; verify that all AS controllers appear in the node list.
3. Download Execution: Execute PLC > Download Changes in CFC on AS 1, then on AS 2; confirm that both downloads succeed without connection warnings.

Limitations and Operational Precautions

Engineering teams must observe the following precautions:
- Never assign multiple WinCC Appl. objects to a single PC Station in HW Config; a PC station supports strictly one WinCC application instance.
- Downloading NetPro connections to an ES while OS Simulation is active can sever active simulation sessions.
- Always validate final license quantities and MLFBs against the applicable Siemens catalog and authorized distributor quotation when procuring engineering hardware and software.

Engineer FAQ

Why did someone tell me I need NetPro connections to download CFC?

This is a common misconception caused by confusing WinCC OS Named Connections with STEP 7 S7ONLINE communication. STEP 7 has always downloaded via direct network addressing without NetPro connection tables.

Can I use TCP/IP direct in PG/PC interface instead of PC internal?

Yes, you can bind S7ONLINE directly to TCP/IP -> [Network Card]. However, in PCS 7, setting PC internal.local.1 is the manufacturer standard because it enables centralized station management and OS simulation.

What happens if two AS controllers in different projects have the same IP address?

Duplicate IP addresses will cause severe network address collisions on Industrial Ethernet. Ensure every AS, OS, and ES has a globally unique IP address across the plant bus.

Technical References

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Related Tags

  • Engineering Station
  • Named Connections
  • S7ONLINE
  • PC Internal
  • NetPro
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