Resolving Missing SWC_MOS Maintenance Override Faceplates and Block Icons in SIMATIC PCS 7 Process Safety

When the SWC_MOS (FB386) block icon and faceplate fail to appear on WinCC graphics pages after selecting 'Generate block icon' in PCS 7 v8.2, it is caused by missing Process Safety typicals in the WinCC project, lack of an assigned picture in the Plant Hierarchy, or absent S7 F-Systems / Safety Matrix OS components. To resolve this, ensure @PCS7Typicals_ProcessSafety.pdl is present in the GraCS directory, verify that the CFC chart resides in an OS-assigned hierarchy folder, and execute 'Create/Update Block Icons' with Process Safety typical templates selected.

Architecture of SWC_MOS in SIMATIC PCS 7 Process Safety

In SIMATIC S7 F-Systems and Safety Matrix, the SWC_MOS (FB386, Software Control - Maintenance Override Switch) block provides controlled bypassing of safety interlocks:
* Functional Purpose:
Allows an authorized maintenance technician to temporarily bypass an F-digital input (e.g., during sensor calibration or instrument replacement) directly from the WinCC OS runtime faceplate without recompiling or downloading F-logic.
* Dual Architecture (F-Block and Standard OS Faceplate):
SWC_MOS resides in the standard/safety boundary in CFC. It interfaces with fail-safe blocks (F_QUITES, F_CH_DI, F_SWC_BO) and communicates operational state to WinCC via standardized OCM tags (S7_m_c := 'true').
* Faceplate Security:
Opening and asserting overrides from the SWC_MOS faceplate requires entering an F-Access password (F_Access) and operating under strict time-limited authorization to comply with IEC 61511 and TÜV certification requirements.

Root Causes for Missing Block Icons and Faceplates in Safety Projects

When an engineer places SWC_MOS in CFC and checks Generate block icon, but no icon appears on the graphic page after OS compile:
1. Missing Process Safety Typicals File:
Standard PCS 7 OS compilation searches @PCS7Typicals_APLV8.pdl, which does not contain the SWC_MOS block icon. The icon definition resides in @PCS7Typicals_ProcessSafety.pdl or @PCS7Typicals_SafetyMatrix.pdl. If the S7 F-Systems OS software was not installed or typicals were not copied, OS compilation cannot find the template.
2. Missing Plant Hierarchy OS Assignment:
Block icons are generated only into the specific WinCC PDL assigned to the Plant Hierarchy folder where the CFC chart resides. If the chart is placed in an unassigned folder or a folder without a configured target picture, no icon can be placed.
3. Incomplete OS Project Editor Run:
If the OS Project Editor has not been executed with the Process Safety option enabled, the necessary faceplate scripts (@pg_SWC_MOS.pdl, @fp_SWC_MOS.pdl) and standard bitmaps are absent from the WinCC project directory.

Configuration Matrix: SWC_MOS Block Attributes and Requirements

The table below outlines mandatory attributes and software components for SWC_MOS:

Parameter / ComponentRequired SettingFunction / PurposeCFC Block AttributeS7_m_c := 'true'Exposes maintenance override tags to WinCC AS-OS compilationBlock PropertyCreate block icon = CheckedDirects OS compiler to instantiate icon in hierarchy pictureBlock Icon Type ID@SWC_MOS/1Maps block to template object in @PCS7Typicals_ProcessSafety.pdlEngineering SoftwareS7 F-Systems v6.2 / v6.3Provides F-libraries, safety compiler, and F-authoring toolsOS Runtime ComponentS7 F-Systems OS (6ES7658-2CX58-0YB5)Installs Process Safety faceplates, scripts, and typicals in WinCCTarget Hierarchy FolderPicture AssignedDefines target user PDL where block icon is physically rendered

Step-by-Step Procedure to Restore SWC_MOS Block Icons and Faceplates

Verify Software Installation:
Ensure SIMATIC S7 F-Systems OS is installed on the Engineering Station and OS Server. This package installs the @pg_SWC_MOS.pdl faceplate files into C:\Program Files (x86)\SIEMENS\WINCC\Options\PDL.
Copy Typicals File to WinCC GraCS:
* Navigate to the Siemens system directory: C:\Program Files (x86)\SIEMENS\WINCC\Options\PDL\ProcessSafety.
* Verify that @PCS7Typicals_ProcessSafety.pdl is present.
* Copy this file into your OS project's GraCS folder if it was not placed there automatically.
Verify Plant Hierarchy Placement:
* In SIMATIC Manager, navigate to the Plant Hierarchy.
* Ensure the CFC chart containing SWC_MOS is inside an hierarchy folder that has an assigned WinCC picture (e.g., Area01_Safety.pdl).
Configure Block Properties in CFC:
* Open the CFC chart containing SWC_MOS.
* Double-click SWC_MOS to open Object Properties.
* Ensure Operator Control and Monitoring is checked.
* Ensure Create block icon is checked.
* Verify that the block icon type displays 1.
Run Create/Update Block Icons:
* Right-click the OS Server object or the root Plant Hierarchy folder.
* Select Plant Hierarchy -> Create/Update Block Icons.
* Confirm that @PCS7Typicals_ProcessSafety.pdl is included in the scanned template list.
* Click OK.
Compile and Download OS:
Execute an OS compilation (Changes only or Entire OS) and download to WinCC OS Runtime.

Configuring Operator Authorization and F-Access Passwords for SWC_MOS

To allow operators to use the SWC_MOS faceplate in runtime:
* WinCC User Administrator:
* Create a user group (e.g., Safety_Engineers) with authorization level 1100 (Higher process controlling) and level 1101 (Safety operating).
* F-Access Password Assignment:
* In the CFC chart, configure the F_CYC_CO block and set the safety password authorization.
* In WinCC Runtime, clicking the override button on the SWC_MOS faceplate prompts the operator for the safety password. Without entering the valid F-Access password, the bypass cannot be enabled.

Verification

To verify that the SWC_MOS faceplate is fully operational:
1. Open the target process graphic in WinCC OS Runtime.
2. Confirm that the SWC_MOS block icon appears with its tag identifier and status indicators.
3. Click the block icon. Confirm that the @pg_SWC_MOS.pdl faceplate opens smoothly without script error dialogs.
4. Enter the F-Access password, select an override duration (e.g., 60 minutes), and activate bypass.
5. Verify that the bypass status updates on the faceplate, the yellow bypass banner appears on the block icon, and an audited event is logged in WinCC Alarm Logging.

Limitations and Operational Precautions

IEC 61511 Bypass Timeouts: Safety standards mandate that maintenance overrides must not remain active indefinitely. Always configure the internal timer on SWC_MOS (MAX_TIME) to automatically revoke bypasses after maintenance concludes.
Simultaneous Overrides Limit: To prevent defeating plant safety integrity, ensure plant operating procedures limit the number of simultaneous active MOS bypasses across the safety matrix.
Licensing Disclaimer: S7 F-Systems Engineering and Runtime packages (6ES7658-2CX58-0YB5 / 6ES7652-0XX08-1XB0) must be validated against the applicable Siemens catalog and authorized distributor quotation.