Troubleshooting Inactive Download Changes Options for WinCC OS Servers in PCS 7

In SIMATIC PCS 7 (V9.0 / V9.1), when attempting to download an OS project to a WinCC OS Server and the 'Download changes' (Änderungen laden) option is disabled or greyed out, the system cannot establish a delta baseline. This occurs because the OS Server is not actively running in Process Mode (WinCC Runtime is stopped), a previous download aborted mid-way, the OS was compiled using 'Entire OS' with memory reset rather than 'Changes only', or local project modifications were made directly on the OS Server. To resolve this, ensure WinCC Runtime is active on the OS Server, compile the OS with 'Changes only' from the ES, verify SIMATIC Shell Terminal Bus connectivity, and ensure project baselines match.

Executive Summary

In 24/7 continuous process industries, the ability to deploy incremental software changes to WinCC Operator Stations without interrupting plant monitoring is paramount. SIMATIC PCS 7 provides the 'Download changes' (Changes Only Download) feature: when minor modifications are made—such as adding a new CFC chart, adjusting alarm parameters, or placing a valve block icon—the Engineering Station (ES) compiles only the modified records and deploys them to redundant OS Servers while WinCC Runtime remains fully active and operational.

However, automation engineers frequently face a critical commissioning roadblock: in SIMATIC Manager, right-clicking the OS Server object and selecting 'PLC > Download...' displays the 'Download changes' radio button completely greyed out, leaving 'Entire project' as the only selectable option. Because a full download mandates deactivating WinCC Runtime and stopping server operations, understanding why delta tracking was invalidated is essential. This guide explains the baseline synchronization mechanics required for delta downloads and outlines the step-by-step remediation procedure to re-enable 'Download changes'.

Architecture and Fundamental Mechanics

The delta compilation and download engine in PCS 7 coordinates changes across multiple relational databases:

Delta Change Tracking Architecture:
- When an OS Server project is compiled for the first time, STEP 7 establishes a synchronized change-tracking baseline between the ES engineering database and the target OS WinCC CS database.
- WinCC maintains internal change log tables (CC_External_...) that track object modifications (tags, alarms, archive tags, and graphics).
Mandatory Prerequisites for 'Download Changes':
- Runtime Execution State: The target OS Server MUST be in Process Mode (WinCC Runtime active). If WinCC Explorer is open in configuration mode with Runtime deactivated, delta download is disabled because the live runtime cache synchronization engine (CCOnlineChange.exe) is idle.
- Consistent Compilation Mode: The AS-OS compilation preceding the download must have been executed with 'Changes only'. If an engineer compiles 'Entire OS' or checks 'With memory reset', delta tracking tables are wiped clean, forcing a full download.
- Inviolability of Target Project: The OS project on the server must NEVER be modified locally. Opening Graphics Designer or Tag Management directly on the OS Server breaks the GUID checksum with the ES, permanently invalidating delta comparison.
- Prior Download Integrity: If a previous delta download was aborted (e.g., due to network disconnection or power glitch), the project marks the server as 'inconsistent state', disallowing further delta changes until a full baseline is re-established.

Step-by-Step Implementation Procedure

Follow these steps to diagnose and re-enable 'Download changes' for PCS 7 OS Servers:

Verify WinCC Runtime State on OS Server:
- Log on to the target OS Server.
- Open WinCC Explorer: verify that the project is running (green runtime indicator active).
- If Runtime is stopped, activate WinCC Runtime. 'Download changes' cannot execute against an inactive runtime station.
Verify AS-OS Compilation Mode on ES:
- Return to SIMATIC Manager on the Engineering Station.
- Right-click the OS Server object and select 'Compile'.
- In the AS-OS Compile Wizard, ensure the radio button 'Changes only' is selected.
- Crucially, verify that the checkbox 'With memory reset' is UNCHECKED.
- Execute compilation. Confirm that compilation finishes with 0 Errors.
Verify SIMATIC Shell Terminal Bus Connection:
- In Windows Explorer on the ES, open the 'SIMATIC Shell' folder.
- Confirm that the target OS Server is visible, reports healthy communication, and that the hosted project name matches the ES project.
- Ensure both ES and OS share identical encryption and Terminal Bus adapter settings.
Inspect Delta Download Status in SIMATIC Manager:
- In SIMATIC Manager Component View, right-click the OS Server object > select 'PLC > Download...'.
- The download dialog will now display 'Download changes' as active and selectable.
- Click 'OK' to initiate the delta transfer.
Performing Controlled Baseline Recovery (If Full Download is Required):
- If a previous interrupted download or local modification permanently broke delta tracking, schedule a brief maintenance window.
- For redundant servers, execute a rolling update: stop Server A, perform a full download ('Entire project'), activate Runtime on Server A, wait for redundancy synchronization, and repeat for Server B without plant shutdown.

Verification

In SIMATIC Manager, initiate 'Download changes': verify that the transfer window reports 'Preparing delta download' and transfers modified tags and pictures.
On the OS Server, observe WinCC Runtime: confirm that runtime graphics refresh seamlessly without screen freezes or communication dropouts.
Open the newly added technological block faceplate on an OS Client: confirm that process variables and alarms update live.
In WinCC Redundancy status, verify that redundancy synchronization completes successfully after the delta download.

Limitations and Operational Precautions

Changes involving new WinCC communication channels, major script modifications, or structural alarm logging reorganization cannot be downloaded via delta download and mandate a full download. Never edit WinCC project files directly on the OS Server. Software runtime packages and engineering licenses should be verified through an authorized Siemens distributor or the Siemens Industry Mall.

Engineer FAQ

Why is 'Download changes' greyed out in SIMATIC Manager?

Because the target OS Server is not in active Runtime, the OS was compiled using 'Entire OS', a previous download failed mid-way, or local edits were made on the server.

Can I perform 'Download changes' while the plant is operating?

Yes. 'Download changes' is specifically designed to deploy modifications while WinCC Runtime remains online without stopping operator supervision.

What happens if someone edits a picture directly on the OS Server?

Local edits alter database checksums and invalidate delta tracking, disabling 'Download changes' until a full download is performed from the ES.

How do I perform a full download on redundant servers without plant downtime?

Perform a rolling download: download to the standby server first, activate it, allow redundancy sync, then switch partner roles and download to the primary server.

Does 'Download changes' automatically update OS Clients?

Yes. The OS Server generates updated server packages, which are automatically reloaded by OS Clients.

Technical References

Related Tags

Download Changes
OS Download
WinCC Runtime
Delta Download
AS-OS Compile
PCS 7 V9.0 SP3

Troubleshooting Inactive Download Changes Options for WinCC OS Servers in PCS 7