Diagnosing WinCC Offline While CFC Remains Online on PCS 7 Engineering Stations

When WinCC Runtime remains offline or fails to establish server connections while CFC charts remain online on a SIMATIC PCS 7 Engineering Station (ES), the fault is caused by a communication failure isolated to the Terminal Bus while the Plant Bus remains operational. The ES utilizes separate physical adapters: an Industrial Ethernet communication processor (such as a CP 1623 running ISO protocol) communicating with the S7-400 CPU on the Plant Bus, and a standard commercial network interface card (NIC) communicating with OS Servers over TCP/IP on the Terminal Bus. Physical disconnection, incorrect adapter binding in Simatic Shell, or corrupted component index assignments in the Station Configuration Editor prevent WinCC from resolving OS Server packages while leaving S7 CPU access intact.

Plant Bus vs Terminal Bus Hardware Separation

A standard SIMATIC PCS 7 Engineering Station (ES) serves a dual functional purpose: it acts as the primary engineering host for the automation controllers (S7-400 / CPU 410-5H) and frequently operates as a supervisory test client or OS Single Station. To perform these roles, the physical host incorporates multiple network interface adapters dedicated to isolated network tiers:

Plant Bus Interface: A specialized Industrial Ethernet communication processor (such as CP 1613, CP 1623 6GK1162-3AA00, or CP 1628 6GK1162-8AA00) connected to the automation controllers. It operates using the ISO transport protocol (layer 2 MAC communication) or ISO-on-TCP.
Terminal Bus Interface: One or more commercial Gigabit Ethernet network interface cards (NICs) connected to the plant server network. It operates using standard IPv4 TCP/IP to exchange runtime data with OS Servers, BATCH Servers, and remote clients.

Because these two communication paths are physically and logically segregated, an engineering station can maintain a fully operational CFC online connection to the S7 controller while WinCC Runtime remains completely offline and unable to connect to OS Servers.

Root Causes of WinCC Offline with CFC Online

When physical maintenance is performed on an Engineering Station—such as cleaning dust from the chassis or replacing cables—hardware disconnections or adapter re-orderings frequently trigger WinCC offline faults:

Diagnostic AreaTypical Fault TriggerPlant Bus (CFC) ImpactTerminal Bus (WinCC) ImpactPhysical CablingTerminal Bus cable unplugged, loose, or swappedNone (CP 1623 cable intact; CFC online)Total loss of OS Server communicationSimatic Shell BindingWindows adapter re-enumeration changed default NICNone (Step 7 uses PG/PC interface directly)Simatic Shell binds to wrong adapter or ISO CPPG/PC Interface SettingsS7ONLINE point altered to internal or wrong CPCFC loses connection to CPUNo impact on WinCC Terminal BusStation Configuration EditorComponent index shifted or WinCC Application stoppedCFC can communicate if PG/PC is directWinCC channel cannot resolve Named ConnectionsWindows Host Resolutionhosts or lmhosts entries missing or IP changedNoneWinCC client cannot resolve OS Server hostnames

If an engineer connects the Terminal Bus cable into a disabled NIC or if Windows renumbers the network cards following driver re-initialization, WinCC fails to locate the OS Server project, while CFC continues to communicate via the CP 1623 without disruption.

Diagnostic Procedure for Simatic Shell and Network Binding

To resolve Terminal Bus connectivity and bring WinCC back online:

Verify Physical Cabling: Behind the Engineering Station, inspect all Ethernet cables. The CP 1623 / CP 1613 typically features two RJ45 ports (or fiber optical interfaces) connected to the Plant Bus switch. The standard motherboard NIC must be connected to the Terminal Bus switch. Verify link LEDs are solid green/amber.
Configure Simatic Shell Adapter:
- Open Windows Explorer and locate This PC -> Simatic Shell.
- Right-click Simatic Shell and select Settings....
- Inspect the adapter listed under Network Adapter. Ensure that the physical network card connected to the Terminal Bus is selected.
- If the CP 1623 (Plant Bus) or an inactive adapter is selected, change the selection to the Terminal Bus commercial NIC.
- Confirm that the IP address displayed matches the configured Terminal Bus subnet.
Verify Host Name Resolution:
- Open Command Prompt and test name resolution by pinging each OS Server by hostname: ping OS_SRV_PRI and ping OS_SRV_STB.
- If pings fail, verify that C:\Windows\System32\drivers\etc\hosts contains the static IP and hostname entries for all servers.

Station Configuration Editor and PG/PC Interface Verification

The internal communication channels between WinCC and Step 7 depend on the Station Configuration Editor (SCE) and the PG/PC Interface:

Inspect Station Configuration Editor:
- Check the Station Configuration Editor icon in the Windows notification tray (taskbar).
- Ensure the station status indicates operational (pencil icon with green arrow or clean rack).
- Verify that the station name in SCE exactly matches the computer name in Windows and the PC Station name in SIMATIC Manager.
- Verify that the WinCC Application component is configured and running.
Verify Set PG/PC Interface:
- In Windows Control Panel, open Set PG/PC Interface.
- Under 'Access Point of the Application', select S7ONLINE (STEP 7).
- For engineering CFC access, ensure it points to PC internal.local.1 (if PC station is configured) or directly to CP1623(ISO).
- Under 'Interface Parameter Assignment Used', confirm that the CP 1623 is active and diagnostics reports 'OK'.

Verification

To verify that WinCC communication is fully restored:
1. In Simatic Shell, expand the tree and verify that all OS Servers, redundant partners, and clients appear with green operational status icons.
2. Open WinCC Explorer on the Engineering Station and activate Runtime.
3. Verify that the runtime interface establishes communication, displays live process values, and clears any '@NC_CONNECT_FAILED' or server connection error banners.
4. Verify that CFC charts can simultaneously go online to inspect block states while WinCC Runtime runs concurrently.

Limitations and Operational Precautions

Never alter the PG/PC interface or Station Configuration Editor settings while an AS download or OS compile is actively underway. Changing the active network adapter in Simatic Shell requires restarting the WinCC Explorer application and re-initializing communication services. Ensure that all modifications maintain strict separation between Plant Bus and Terminal Bus subnets to prevent network bridging.

Engineer FAQ

Why can CFC connect to the PLC while WinCC cannot connect to the server?

Because CFC connects to the controller via the Plant Bus (CP 1623 running ISO protocol), while WinCC client communicates with OS Servers via the Terminal Bus (standard commercial NIC running TCP/IP).

What should the PG/PC interface be set to on an Engineering Station?

In a properly configured PCS 7 PC Station, S7ONLINE is typically mapped to PC internal.local.1. This allows the Station Configuration Editor to route communication internally to the CP 1623 or WinCC Application.

How do I know if Simatic Shell is bound to the wrong adapter?

In Simatic Shell -> Settings, check the selected network card. If it shows the CP 1623 adapter or an internal loopback adapter instead of the Terminal Bus NIC, WinCC cannot communicate with remote servers.