Controlling Motor and Valve Operating Modes on PLC Startup via Feature.Bit0 in PCS 7 APL

In SIMATIC PCS 7 Advanced Process Library (APL), motors and valves automatically reverting to Manual mode following an S7-400 CPU restart is governed by block parameter Feature.Bit0 (Set startup characteristics). By factory default, Feature.Bit0 = 0, forcing all technological blocks (MotL, MotS, VlvL, VlvMotL, PIDConL) to start in Manual mode and neutral position for plant safety after a power outage. To configure motors and valves to retain their pre-restart operating modes (Automatic, Manual, or Local) upon PLC startup, set Feature.Bit0 = 1. This parameter can be configured in bulk across the entire project using the Process Object View.

CPU Startup Execution and Technological Block Initialization in OB100

When an S7-400 automation system (such as CPU 416-3 PN/DP 6ES7416-3ES07-0AB0 or CPU 410-5H 6ES7410-5HX08-0AB0) powers up or recovers from a STOP-to-RUN transition, the operating system executes Organization Block 100 (OB100 - Complete Restart). During OB100, initialization code for every instantiated APL block executes for a configured number of startup cycles defined by the input parameter RunUpCyc (typically 100 cycles).

In industrial plants with hundreds of drives, control valves, and feed pumps, commissioning engineers often face an operational dilemma: after a momentary power dip or planned controller reboot, all equipment unexpectedly defaults to Manual mode (ManMod). Operators must manually navigate through dozens of graphic screens and faceplates to restore automatic sequence control. In the Siemens Advanced Process Library, this behavior is an intentional safety safeguard controlled by the technological Feature bit structure.

APL Startup Feature Architecture: Feature.Bit0 vs Feature.Bit1

The APL technological blocks utilize a 32-bit structured word input named Feature to configure behavioral characteristics without modifying underlying algorithm code. Startup behavior is governed specifically by bits 0 and 1:

Feature.Bit0 = 0 (Factory Default - Safe Startup):
Motors (MotL, MotS, MotRevL): Starts in Manual mode and in neutral state (Stop command active, Start = 0).
Valves (VlvL, VlvMotL, VlvAnL): Starts in Manual mode and in neutral state (Close command active, Close = 1).
Controllers (PIDConL, PIDConR): Starts in Manual mode; internal setpoint (SP_Int) is active.
Rationale: Prevents unexpected machinery restarts or dangerous fluid flows when power returns unexpectedly.
Feature.Bit0 = 1 (Retentive Operating Mode):
Technological blocks start with the last stored values stored in CPU retentive work memory immediately prior to shutdown.
If a motor or valve was operating in Automatic mode before the power loss, it resumes operation in Automatic mode.
Controllers retain their last operating mode, last setpoint value, and last manual manipulated variable.
Feature.Bit1 (Reaction to Operating State of Technological Block):
Defines how the block responds if the physical equipment is in an intermediate state (e.g. valve moving or motor spinning down) during startup.

Comparison of Startup Characteristics across APL Technological Blocks

The following table summarizes the startup reaction of key APL technological blocks based on Feature.Bit0 configuration:

APL Block TypeBlock NameDefault (Feature.Bit0 = 0)Configured (Feature.Bit0 = 1)Safety ImplicationLarge MotorMotL (FB1850)Manual Mode; Motor StoppedRetains Auto/Man mode; resumes stateHigh; uncommanded motor start if Bit0=1Reversing MotorMotRevL (FB1851)Manual Mode; Motor StoppedRetains Auto/Man mode and directionHigh; directional restart riskTwo-Way ValveVlvL (FB1899)Manual Mode; Valve ClosedRetains Auto/Man mode; retains positionModerate; unintended line fillingMotorized ValveVlvMotL (FB1898)Manual Mode; Stop CommandRetains Auto/Man mode; retains positionModerate; stroke command continuationPID ControllerPIDConL (FB1874)Manual Mode; Internal SPRetains Auto/Man mode; retains SPCritical; loop transient suppressionAnalog MonitoringMonAnL (FB1845)Starts with initial process valueRestores historical limits and filterLow; alarm suppression during RunUpCyc

Step-by-Step Procedure to Bulk-Configure Feature.Bit0 via Process Object View

Manually modifying Feature.Bit0 across hundreds of individual CFC charts is prone to errors. Use the SIMATIC Manager Process Object View (POV) to bulk-parameterize blocks in minutes:

Open the Process Object View:
- In SIMATIC Manager, select View -> Process Object View (or press Ctrl+Shift+P).
- In the left plant hierarchy tree, select the root project or plant unit folder containing the target controllers.
Filter by Block Type:
- Select the Parameters tab at the bottom of the right-hand pane.
- In the filter bar at the top, set the block filter to MotL (repeat subsequently for VlvL and PIDConL).
Locate and Modify Feature Bit 0:
- Scroll horizontally to find parameter column Feature.Bit0 (or parameter Feature depending on view configuration).
- For individual bits, expand the Feature structure. Select the Bit 0 column.
- Highlight the column, enter 1 (or check the box for True), and use keyboard fill-down (Ctrl+D) to apply the change across all listed motors and valves.
Compile and Download Changes to the AS:
- Close the Process Object View.
- Open the CFC Editor, select Chart -> Compile -> Changes only.
- Select PLC -> Download -> Changes only. Delta download executes bumplessly in CPU RUN mode.

Verification

Verify the startup configuration in a test environment or scheduled maintenance window:
1. Place a designated test motor (MotL) and control valve (VlvL) into Automatic mode via their WinCC faceplates.
2. Perform a planned CPU Warm Restart / Complete Restart via STEP 7 (PLC -> Diagnostic/Setting -> Operating Mode -> Restart) or power cycle the test rack.
3. Once the CPU completes OB100 and enters cyclic RUN, inspect the faceplate operating mode indicators.
4. Confirm that the motor and valve remain in Automatic mode without operator intervention.
5. Verify that interlock signals (Intlock, Permit, Protect) are evaluated correctly following expiration of the RunUpCyc period.

Limitations and Operational Precautions

Safety Hazard of Automatic Machinery Restart: Enabling Feature.Bit0 = 1 on rotating equipment (conveyors, crushers, agitators) can violate regional machine safety regulations (e.g. OSHA, EN ISO 13849). Personnel could be exposed to unexpected starts upon power restoration. Always conduct a formal Process Hazard Analysis (PHA) before modifying default startup behavior.
Interlock Evaluation Timing: During RunUpCyc, APL blocks ignore non-essential interlocks to prevent false tripping while field transmitters stabilize. Ensure RunUpCyc is matched to field transmitter boot times (typically 5 to 10 seconds).
SFC Sequence Coordination: If equipment is driven by Sequential Function Charts (SFC), verify that the SFC step logic properly coordinates with blocks restarting in Auto mode to prevent step sequencing mismatches.

Engineer FAQ

What is the difference between Feature.Bit0 and Feature.Bit1?

Feature.Bit0 determines whether the block starts in Manual mode (0) or with the last stored operating mode (1). Feature.Bit1 specifies how the block responds if the physical equipment is in an intermediate state (e.g., valve transitioning) during startup.

Why is Manual mode the factory default for APL blocks?

Manual mode is the internationally recognized fail-safe default. In the event of an unplanned power blackout, defaulting to Manual ensures that massive industrial machinery and chemical feeds do not start up simultaneously when power is restored.

Can I configure Feature.Bit0 to start in Auto mode only if an external signal is active?

Yes. Instead of setting Feature.Bit0 = 1, you can leave Feature.Bit0 = 0 and interconnect the block's AutModLi (Auto Mode via Link) input to an automated startup sequence block that systematically restores Auto mode after verifying field safety permissives.