Resolving AS Download Error: Connection Cannot Be Established to Target Group

The error 'Online: Connection cannot be established to the target group' (Verbindung kann nicht bis zur Zielgruppe aufgebaut werden) when downloading from an Engineering Station (ES) to an Automation System (AS)—while OS downloads succeed—occurs because the local communication routing from the ES PC Station is uncompiled or misconfigured in the Station Configuration Editor. When using access point 'PC internal (local)', the ES PC Station object in SIMATIC Manager must have its hardware and connections explicitly downloaded to its local Station Configuration Editor and NetPro. Furthermore, the active computer name must match the ES PC Station name, visually confirmed by a yellow arrow on the ES in SIMATIC Manager.

Local Routing Mechanisms via 'PC Internal (Local)' Access Point

In SIMATIC PCS 7, downloading program logic to an S7-400 or CPU 410-5H controller from the Engineering Station relies on the SIMATIC NET communication subsystem. In standard PCS 7 architectures, the engineering workstation is modeled as a configured PC Station (WinCC Appl. and IE General / CP 1623).

When the PG/PC Interface access point S7ONLINE is assigned to PC internal (local), STEP 7 does not communicate directly through a physical Ethernet card driver. Instead, communication is routed internally through the Station Configuration Editor (SCE), which looks up the configured S7 connections and routing tables compiled in NetPro. If this local routing chain is broken, STEP 7 halts with the fatal error: 'Online: Connection cannot be established to the target group.'

Why OS Downloads Succeed While AS Downloads Fail

Engineers are often baffled when an OS download completes with 100% success while the AS download immediately aborts:

OS Download Protocol: Downloading an Operator Station uses standard Windows operating system network sharing (SMB/RPC) and Microsoft SQL Server database attachment over the Terminal Bus. It does not rely on the S7ONLINE communication stack.
AS Download Protocol: Downloading to the AS controller requires the S7 communication protocol over Industrial Ethernet. If the local PC Station configuration was never downloaded from NetPro into the ES Station Configuration Editor, the ES kernel cannot route packets to the physical Plant Bus.

The Yellow Arrow Indicator on the ES PC Station

SIMATIC Manager provides an unmistakable visual indicator of PC station synchronization:

Computer Name Matching: The configured name of the PC Station object in the multiproject tree must match the physical Windows computer name of the Engineering Station character-for-character.
The Yellow Arrow: When the names match and the access point is correctly set to PC internal (local), SIMATIC Manager renders a small yellow arrow pointing to the ES PC Station icon. If the yellow arrow is absent, the ES does not recognize itself as the local station, and communication through PC internal fails.

Comparison of PG/PC Interface Access Points

The table below contrasts different access point configurations in Set PG/PC Interface on the Engineering Station.

Access Point SettingHow Communication RoutesStation Configurator Required?Yellow Arrow Displayed?Recommended Use CasePC internal (local)Routes through Station Configurator & NetProYES (Mandatory SCE download)YESOfficial PCS 7 Standard ArchitectureTCP/IP -> Physical NICBypasses Station Configurator; direct IP socketNo (Direct network card binding)NoDirect testing / Standalone STEP 7ISO -> CP 1623Layer-2 MAC transport via dedicated CPYesYes (If configured as CP)Pure ISO Plant Bus architecturesPLCSIM.TCPIP.1Routes to virtual S7-PLCSIM controllerNoNoOffline simulation on engineering station

Step-by-Step Procedure to Restore AS Download Communication

Follow this procedure to re-establish the communication chain and eliminate the target group connection error:

Verify Computer Name and Yellow Arrow:
- Check your Windows computer name in System Properties.
- In SIMATIC Manager Component View, ensure the ES PC Station is named identically.
- Confirm that the yellow arrow appears on the ES PC Station object.
Configure Local Station Configuration Editor:
- On the ES, open the Station Configuration Editor (Komponenten-Konfigurator).
- Ensure the station name matches, and verify virtual slots (Slot 1: WinCC Appl., Slot 2: IE General or CP 1623).
- In SIMATIC Manager, right-click the ES PC Station -> select PLC -> Configure... to deploy configuration.
Download NetPro Connection Tables to the ES:
- Open NetPro from the multiproject root.
- Select Network -> Save and Compile (Compile and check everything).
- Highlight the ES PC Station in NetPro.
- Select menu PLC -> Download to Current Project -> Selected Station.
- This loads the compiled routing database directly into the local Station Configuration Editor.
Verify PG/PC Interface and Execute Download:
- Open Set PG/PC Interface: verify access point S7ONLINE is set to PC internal (local).
- In SIMATIC Manager, select the AS CPU and click PLC -> Download.
- The connection establishes immediately, and download proceeds without errors.

Verification

Verify communication restoration through the following checks:
1. In SIMATIC Manager, select the CPU and open PLC -> Module Information: verify that online diagnostic tabs populate instantly.
2. In NetPro online view, verify that the S7 connection from ES to AS displays active 'Connected' status.
3. Perform a CFC delta download: confirm that the download dialog reaches completion.
4. Open an online CFC chart: verify that live process tags update dynamically in test mode.

Limitations and Operational Precautions

If using a physical laptop as a temporary Engineering Station, switching between Wi-Fi and hardwired docking station Ethernet adapters alters the active Windows MAC/IP bindings. If IE General is bound to a disconnected adapter in the Station Configuration Editor, all downloads through PC internal will abort. Always bind IE General to the active physical network card connected to the Plant Bus.

Engineer FAQ

Why does 'PC internal' fail if I can ping the PLC successfully?

Ping tests basic Windows IP network connectivity. However, 'PC internal' routes through the SIMATIC NET protocol stack and Station Configuration Editor. If NetPro connections were never downloaded locally, S7 routing fails even if ping succeeds.

Can I temporarily bypass this error by switching S7ONLINE to my physical network card?

Yes. Switching S7ONLINE directly to 'TCP/IP -> [Network Card]' in Set PG/PC Interface allows direct downloading to the CPU, but it bypasses Named Connections and disables OS Simulation on the ES.

What does the 'target group' mean in the Siemens error message?

'Target group' refers to the communication subsystem and subnet path defined in NetPro. The error indicates that the local routing table contains no path to reach that subnet.