Managing Operator Prompt Indications on SFC Types After Controller Restarts in PCS 7

Following an Automation Station restart (STOP to RUN transition) or CPU warm restart in SIMATIC PCS 7 V9.1, instantiated SFC types display an operator prompt state indicated by a purple 'O' icon on WinCC OS faceplates and overview navigation keys. This deterministic safety behavior prevents automated unexpected resumption of active phases; operators must evaluate plant conditions and use SFC Visualization to acknowledge, resume, or abort the sequence to restore normal continuous operation.

Operating State Logic of SFC Types During Controller Restarts

Sequential Function Charts (SFC) in SIMATIC PCS 7 manage state-based and recipe-driven phase execution. Unlike continuous PID loops that immediately recalculate process outputs upon controller restart, sequential control requires strict state validation to prevent mechanical damage or process hazards:
* When an S7-400 or CPU 410-5H controller transitions from STOP to RUN, organization blocks OB100 (warm restart) and OB102 (cold restart) initialize system memory.
* If an SFC instance was in an active executing state (such as Starting, Run, or Holding) prior to the CPU stop, the SFC operating state logic (OSL) detects the disruption upon restart.
* By design, the SFC cannot automatically assume that physical plant conditions (valves, pumps, heaters, pressure vessels) remain synchronized with the pre-stop step.

Root Cause of the Purple 'O' Operator Prompt Indication

The purple "O" icon displayed on the WinCC runtime overview area and APL block icons indicates an active Operator Prompt:
* Deterministic Halt: The SFC operating state logic halts automatic step stepping and sets the status bit OpEn = 1 (Operator Prompt Active).
* Alarm Generation: The underlying SFC block instance generates a high-priority system message categorized as an operator prompt, routing a visual notification to the WinCC alarm banner and navigation keys.
* Safety Lockout: The sequence remains frozen in the prompt state until an authorized operator inspects field conditions and manually commands the sequence forward or terminates the batch phase.

Configuring SFC Type Restart Characteristics in SFC Editor

Engineers can customize how an SFC type behaves following a CPU restart through the SFC Editor:
1. In SIMATIC Manager, open the Master Data Library and open the target SFC Type.
2. Select SFC -> Properties and navigate to the Options (or Operating State Logic) tab.
3. Locate the Restart Characteristics configuration:
* Manual Operator Decision (Default): Forces the SFC into the operator prompt state, requiring manual intervention via faceplate.
* Automatic Abort on Restart: Transitions the SFC directly into the Aborting or Stopped state upon CPU warm restart, running safe shutdown steps.
* Resume from Pre-Stop Step: Resumes execution from the interrupted step (applicable only when physical process safety permits automated resumption).
4. Save and compile the SFC type, update block types across all project charts via Options -> Charts -> Update Block Types, and download changes to the AS.

Operator Acknowledgment Workflow in WinCC SFC Visualization

When operators encounter the purple "O" indication in WinCC runtime:
1. Click the purple O navigation key or the affected SFC block icon to open the SFC Faceplate.
2. Inspect the Actual State and Step Details displayed in the SFC Visualization window.
3. Review field sensors and confirm whether the unit can safely continue or must be drained/purged.
4. If continuation is safe, click the Resume button on the faceplate toolbar. The SFC clears the operator prompt flag, extinguishes the purple "O", and proceeds with phase execution.
5. If continuation is hazardous, select Abort or Stop to trigger safe shutdown sequences and return the SFC to Idle.

Verification

In a test environment or during a scheduled outage, start an SFC sequence and advance it to an intermediate active step.
Toggle the controller operating switch to STOP, wait 10 seconds, and switch back to RUN.
Observe the WinCC runtime overview area: confirm that the purple "O" icon appears on the navigation area button and block icon.
Open the SFC faceplate, click Resume, and verify that the purple icon disappears and the step timer increments normally.

Limitations and Operational Precautions

Never configure batch-critical SFC types to resume automatically on restart without implementing field interlocks that verify equipment positioning and vessel contents.
Operator prompt alarms cannot be cleared merely by pressing the global message acknowledge button; an explicit command must be sent to the SFC instance via faceplate.
In SIMATIC BATCH applications, an unacknowledged SFC prompt halts the higher-level recipe unit allocation until resolved.

Engineer FAQ

Why does the purple 'O' appear on all SFC faceplates simultaneously after a power outage?
Because all active SFC instances detected an uncommanded CPU restart and halted execution to demand operator verification of physical plant status.
Can the purple 'O' indication be disabled globally in PCS 7?
No, the operator prompt indication is a core safety mechanism of the PCS 7 APL and SFC visualization architecture.
What is the difference between an SFC Chart and an SFC Type regarding restart settings?
SFC Types define reusable state logic with centralized restart properties configured in the library; SFC Charts configure individual chart properties directly.
Which WinCC user authorization is required to acknowledge an SFC operator prompt?
The operator must hold Process Controlling authorization (typically Authorization Level 5 or 6 in WinCC User Administrator).
What happens to step timers inside the SFC during a CPU stop?
Step timers freeze during CPU STOP and retain their elapsed time unless the SFC is configured to reset on restart.
Can an external PLC signal automatically clear the operator prompt without human intervention?
Yes, by connecting a supervisory handshake signal to the SFC command input pins (RESUME_OP or START_OP) in the CFC chart.
Where in the WinCC alarm screen do operator prompt messages appear?
They appear in the Process Messages or Operator Prompts list, filtered with class "Operator Prompt".
Does a redundant AS switchover trigger the SFC operator prompt?
No, a bumpless switchover between redundant CPU 410-5H controllers preserves SFC operating state without triggering an operator prompt.
What block generates the WinCC alarm for an SFC Type instance?
The underlying system block generated by the SFC compiler (associated with FB300 / SFC runtime engine) generates the message.
How does SIMATIC BATCH react when an SFC enters the operator prompt state?
SIMATIC BATCH marks the associated recipe phase as "Waiting for Operator" and pauses recipe execution until acknowledged.

Technical References

SIMATIC PCS 7 SFC for S7 / PCS 7 Operating Manual
SIMATIC PCS 7 SFC Visualization Manual (V9.0 / V9.1)
Siemens Industry Online Support Entry: Operator Prompt Handling in SFC Types (Entry ID 298513)
SIMATIC PCS 7 Advanced Process Library (APL) Function Manual

Related Tags

PCS 7, SFC, SFC Types, Operator Prompt, S7-410, Warm Restart, SFC Visualization, APL, WinCC, Batch

Managing Operator Prompt Indications on SFC Types After Controller Restarts in PCS 7