AS and OS Compilation and Delta Download Rules When Relocating APL Blocks Across CFC Charts

In SIMATIC PCS 7, relocating an APL block (such as cutting and pasting MotL) from one CFC chart into its own dedicated chart changes its hierarchical tag path (from OldChart/MotL to NewChart/MotL). The Automation System (AS) requires a CFC compile and download of changes, after which PLC logic continues operating normally in the controller. However, the existing WinCC OS block icon and faceplate will disconnect (showing invalid quality code 16#00) until an OS Compilation and OS Download Changes are executed. Relocating blocks creates new WinCC tags and deprecates old ones; therefore, BOTH AS download of changes and OS delta download are mandatory to restore runtime visualization and operator control.

Executive Summary

During plant commissioning or restructuring, engineers frequently refactor overloaded CFC charts by cutting and pasting function blocks (such as the APL motor block MotL) into dedicated technological charts. While the PLC program compiles cleanly with 'Changes only' and downloads in RUN mode, engineers often question whether WinCC OS compilation and download are strictly required. Because PCS 7 enforces a strict hierarchical naming convention derived from the Plant Hierarchy and chart titles, moving a block alters all associated OS tag names. This article establishes the technical mechanics of block relocation, details AS/OS compilation rules, and explains how to execute online delta downloads without disrupting running processes.

Architecture and Fundamental Mechanics

SIMATIC PCS 7 automates HMI tag generation through the technological hierarchy. In CFC, every block instance receives a system-wide unique identifier formatted as:
<Plant_Hierarchy_Folder>/<CFC_Chart_Name>/<Block_Instance_Name>.

When MotL is moved from Chart_A to Chart_B:
1. AS Domain: In the controller's symbol table and DB mapping, the block's instance data block is reassigned. The CFC compiler handles this via incremental compile ('Changes only') and generates delta download blocks. Once downloaded, the controller executes the motor logic seamlessly in its new cyclic OB execution group.
2. OS Domain: The WinCC tag management database contains historical tags registered under Chart_A/MotL.*. The WinCC process picture graphic contains an APL block icon linked to tag prefix Chart_A/MotL. When the AS download completes, the controller no longer updates tags under Chart_A/MotL. As a result, the runtime block icon displays an invalid quality code (16#00 or a yellow/blue disconnected badge), and opening the faceplate shows frozen values and disabled operator buttons.

To restore operation:
- An OS Compile (Changes only) is mandatory to delete the obsolete Chart_A/MotL tags and generate the new Chart_B/MotL tags and message assignments.
- An OS Download (Changes only / Delta Download) is mandatory to transfer the updated dBase configuration to the active OS Server pair.
- Crucially, in redundant OS architectures, OS Delta Download executes online in RUN mode without taking OS servers offline or interrupting plant visualization.

Step-by-Step Implementation Procedure

Relocate Block in CFC Editor:
a. Open the original CFC chart (Chart_A), select the MotL block, and verify all external interconnections.
b. Cut (Ctrl+X) the MotL block.
c. Create and open the new dedicated CFC chart (Chart_B), then paste (Ctrl+V) the block.
d. Re-establish any necessary inter-chart connections to interlocks or channel drivers.
Compile and Download the Automation System (AS):
a. In CFC Editor, select Chart -> Compile -> Chart as Program....
b. Choose 'Changes only' and ensure 'Generate module drivers' is selected if I/O drivers were altered.
c. In SIMATIC Manager, select the CPU and execute PLC -> Download -> Changes... in RUN mode.
d. Verify in CFC test mode that the motor block executes and responds to physical inputs.
Execute OS Compilation:
a. In SIMATIC Manager Component View or Plant View, right-click the OS Server project and select 'Compile'.
b. Select 'Changes only' for scope and ensure the target AS is checked.
c. Complete the compilation. The compiler removes legacy tags and inserts Chart_B/MotL tags into WinCC Tag Management.
Update Block Icons in Process Graphics:
a. In Plant View, right-click the plant hierarchy folder containing the process pictures and select Plant Hierarchy -> Create/Update Block Icons.
b. The tool updates the block icon's tag and tagname properties to point to Chart_B/MotL.
Execute OS Delta Download:
a. In SIMATIC Manager, right-click the OS project and select PLC -> Download.
b. Choose 'Changes' (Delta Download). The engineering system downloads the modified tag dictionary and graphics to the OS servers in RUN mode without shutting down runtime.

Verification

In WinCC Runtime on the OS Client, navigate to the motor's process graphic: verify that the block icon displays healthy status without diagnostic badges or disconnected overlays.
Click the block icon to open the MotL faceplate: verify that live process values update dynamically.
Issue a manual start/stop command from the faceplate and verify immediate response in the controller.
Check WinCC AlarmControl: generate a test trip and confirm that alarm messages attribute correctly to Chart_B/MotL.

Limitations and Operational Precautions

If the block icon was manually modified or has 'Create block icon' disabled in the CFC block properties, automated block icon updating will not reconnect the graphic; the tag and tagname properties must be adjusted manually in Graphics Designer. Performing an OS 'Entire Project' download instead of 'Changes' requires stopping WinCC Runtime; always ensure 'Changes' is selected for online production environments.

Engineer FAQ

Will the motor continue running in the PLC if I only do an AS download?

Yes. The controller executes the logic uninterrupted once the AS download of changes is complete; only HMI visualization and operator control on the OS will be disconnected.

Why does the block icon show invalid quality code after moving the block?

Because the WinCC block icon is still pointing to the old tag prefix (OldChart/MotL), which no longer exists in the controller data blocks.

Does an OS download of changes require shutting down redundant OS servers?

No. WinCC OS 'Download Changes' (Delta Download) transfers updates online while redundant servers remain in RUN mode with zero downtime.

What happens to historical trend data when a block is relocated?

Historical trend curves linked to the old tag name will stop logging; new archive entries begin under the new tag name unless archive tag names are manually preserved.

Can I move an entire CFC chart to a different plant folder without breaking OS tags?

Moving an entire chart changes its Plant Hierarchy path, which alters the OS tag prefix identically to moving an individual block, necessitating OS compile and delta download.