Why Project Download to OS via CP 1623 Fails While IE General Succeeds in PCS 7 V8.1

In SIMATIC PCS 7 V8.1, project downloads from the Engineering Station (ES) to an OS Station succeeding over IE General (standard onboard network adapter) but failing when attempted over the CP 1623 is caused by the strict physical and logical separation between the Terminal Bus and Plant Bus. In PCS 7 architecture, OS project downloads utilize Windows File Sharing (SMB), DCOM, and Simatic Shell, which operate exclusively over the Terminal Bus. The CP 1623 is a dedicated Industrial Ethernet communications processor designed strictly for the Plant Bus to execute S7 communication with AS controllers. Simatic Shell must bind exclusively to the Terminal Bus network adapter (IE General); attempting to route OS project downloads across the CP 1623 plant bus interface violates PCS 7 design rules and is blocked by the engineering environment.

Executive Summary

During the commissioning of multi-station PCS 7 V8.1 architectures, automation engineers often install dual network adapters on their PC stations: an industrial communication processor (CP 1623 / CP 1613) and a standard commercial network interface card (IE General). A frequent puzzle arises when attempting to download the WinCC OS project from the ES: while the download completes smoothly when targeting the IE General IP address, selecting the CP 1623 path fails completely, even though ping commands to the CP 1623 succeed. This technical guide explains the architectural boundaries between Plant Bus and Terminal Bus, clarifies the protocol requirements of Simatic Shell and OS downloads, and details the correct network bindings.

Architecture and Fundamental Mechanics

The communication architecture of SIMATIC PCS 7 enforces rigid segregation between process control and operational supervisory data:
1. The Plant Bus vs Terminal Bus Paradigm:
- Plant Bus (Process Communication): Connects AS controllers to OS Servers and Engineering Stations. Operates over Industrial Ethernet using ISO Transport Protocol (MAC-based) or ISO-on-TCP (RFC 1006). Hardware: CP 1623, CP 1613, or CP 443-1.
- Terminal Bus (Supervisory and Engineering Communication): Connects Engineering Stations, OS Servers, OS Clients, and Process Historians. Operates over standard commercial TCP/IP. Hardware: standard gigabit network adapters (IE General).
2. The OS Project Download Mechanism:
- Executing PLC -> Download on a WinCC Application object from SIMATIC Manager does not use industrial S7 communication.
- Instead, it initiates a high-level file deployment sequence:
a. Windows NetBIOS / SMB file transfer to copy graphic files (.pdl), scripts (.c), and database templates across the Windows network share.
b. DCOM and RPC calls to register the project in Microsoft SQL Server (.\WINCC).
c. Station discovery managed by Simatic Shell.
3. Why CP 1623 Cannot Support OS Project Downloads:
- The CP 1623 is optimized for hardware-accelerated S7 communication (Hardnet). In PCS 7, it is assigned exclusively to the Plant Bus subnet in NetPro.
- Simatic Shell can only bind to a single network adapter at a time. By design, Simatic Shell must bind to the Terminal Bus.
- If an engineer attempts to initiate an OS download through the CP 1623 interface, Simatic Shell cannot resolve the remote target, and Windows SMB sharing fails to authenticate, aborting the transfer.

Step-by-Step Implementation Procedure

Verify Physical Network Separation:
a. Inspect the physical network cabling on the Engineering Station and all OS stations.
b. Ensure that the standard onboard network ports (IE General) connect to the Terminal Bus switch.
c. Ensure that the CP 1623 ports connect to the industrial Plant Bus switch (e.g., SCALANCE X-300/X-400).
d. Confirm that the Terminal Bus and Plant Bus utilize separate, non-overlapping IP subnets (e.g., Terminal Bus = 192.168.1.x, Plant Bus = 192.168.2.x).
Configure Simatic Shell Exclusively on the Terminal Bus:
a. On the Engineering Station and all OS stations, open Windows Explorer.
b. Navigate to 'This PC', right-click Simatic Shell, and select Settings....
c. In the network adapter selection window, strictly select the Terminal Bus network adapter (IE General).
d. Never select the CP 1623 or NDIS adapter associated with the plant bus.
e. Click 'OK' and verify that all PC stations populate in the Simatic Shell tree view.
Configure Windows Network Adapter Priorities and Metrics:
a. In Windows Control Panel, open Network Connections.
b. Rename adapters to Terminal_Bus and Plant_Bus.
c. In Terminal_Bus properties, ensure 'File and Printer Sharing for Microsoft Networks' and 'Client for Microsoft Networks' are checked.
d. Ensure that a default gateway is configured only on the Terminal_Bus adapter, leaving the Plant_Bus gateway blank.
Configure PC Station Properties in SIMATIC Manager:
a. In SIMATIC Manager on the ES, open HW Config for the OS PC Station.
b. Verify that Slot 1 contains WinCC Application.
c. Verify that Slot 2 contains IE General assigned to the Terminal Bus subnet.
d. Verify that Slot 3 contains CP 1623 assigned to the Plant Bus subnet.
e. In the WinCC Application properties under 'Target OS and Standby OS Computer', ensure the destination path points to the Terminal Bus network share: e.g., \\OS_SRV1\WinCC_Project.
Execute OS Download via Terminal Bus:
a. In SIMATIC Manager, right-click the OS project object under the PC Station.
b. Select PLC -> Download.
c. The transfer executes reliably over the high-speed Terminal Bus using IE General.

Verification

In SIMATIC Manager, initiate 'PLC -> Download' to the OS station: verify that file copying and SQL database registration complete with 0 errors.
In Simatic Shell, verify that all OS and ES stations show green status icons.
In WinCC Runtime on the OS station, open 'Channel Diagnosis': confirm that S7 communication to the AS controllers continues uninterrupted over the CP 1623 plant bus while client-server data flows over the terminal bus.

Limitations and Operational Precautions

Never bridge the Plant Bus and Terminal Bus within Windows or through unmanaged switches. Bridging these subnets causes broadcast loops, degrades controller communication deterministic performance, and violates IEC 62443 security zoning.

Engineer FAQ

Why does OS project download fail over CP 1623?

Because OS project downloads require Windows File Sharing (SMB) and Simatic Shell, which are designed exclusively for the Terminal Bus (IE General).

What is the primary function of the CP 1623 card?

The CP 1623 is a dedicated communications processor designed for high-availability S7 communication between OS servers and AS controllers on the Plant Bus.

Can Simatic Shell bind to both network cards simultaneously?

No. Simatic Shell can only bind to a single network adapter, which must strictly be the Terminal Bus adapter.

Why can I ping the CP 1623 if the download fails?

Ping only verifies basic ICMP network connectivity; OS downloads require Windows file sharing, RPC, and Simatic Shell discovery, which are disabled on the plant bus.