C135 PCS 7 (PCS7)
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Troubleshooting SFC-to-MotL Automatic Mode Transitions in SIMATIC BATCH: ModLiOp and Feature Bit 4 Handshakes

Troubleshooting SFC-to-MotL Automatic Mode Transitions in SIMATIC BATCH: ModLiOp and Feature Bit 4 Handshakes

In SIMATIC PCS 7 and SIMATIC BATCH, when an SFC step successfully completes but fails to switch an APL motor block (MotL, FB1850) into Automatic mode despite configuring ModLiOp = 1 and AutModLi = 1, the cause is an edge-detection requirement on AutModLi or an active technological interlock. By default, MotL evaluates AutModLi as a 0-to-1 rising edge signal (Feature.Bit4 = 0). If AutModLi remains statically TRUE across recipe steps, subsequent mode switches fail. To resolve this, configure Feature.Bit4 = 1 ('Switch to automatic mode via level-sensitive signal') so MotL maintains automatic mode whenever AutModLi = 1, or pulse AutModLi from 0 to 1 in the SFC step initialization.

Table of Contents

Executive Summary

During batch recipe execution in SIMATIC BATCH, an Equipment Phase (EPH) or unit SFC sequence coordinates field actuators by commanded mode changes (switching drives from Manual to Automatic, and asserting start commands). Commissioning engineers frequently encounter an issue where the batch recipe runs to completion, but subordinate motors (such as agitators or feed pumps controlled by MotL) fail to start. In CFC, engineers observe that while ModLiOp = 1 and AutModLi = 1 are set by the SFC step action, MotL remains stubbornly in Manual mode. This guide clarifies the operating mode state machine of APL technological blocks, explains Feature.Bit4 edge vs level mechanics, and outlines robust SFC command handshakes.

Architecture and Fundamental Mechanics

The operating mode transition architecture of APL blocks (MotL, VlvL) enforces strict authorization and trigger rules:
1. Operating Mode Precedence and Handshake Inputs:
- ModLiOp (Link Mode Operator): Determines whether mode switching is controlled by operator faceplate commands (ModLiOp = 0) or programmatic CFC/SFC signals (ModLiOp = 1).
- AutModLi: Programmatic command to switch to Automatic mode.
- ManModLi: Programmatic command to switch to Manual mode.
2. Edge vs. Level Sensitive Switching (Feature.Bit4):
- Default Behavior (Feature.Bit4 = 0 - Edge Sensitive): The block requires a discrete FALSE $\rightarrow$ TRUE transition on AutModLi while ModLiOp = 1. If an SFC step assigns AutModLi = 1 while it was already held high from a preceding step, no rising edge occurs. The internal state machine ignores the command, leaving the motor in Manual mode.
- Level-Sensitive Behavior (Feature.Bit4 = 1): When enabled, AutModLi = 1 continuously forces the block into Automatic mode as long as the signal remains high and higher-priority conditions (such as Out of Service or Emergency Stop) are inactive.
3. Interlock and Safety Permissives:
Even if mode switching succeeds, MotL will not assert run outputs (Start.Value = 1) in Automatic mode unless all interlock permissives are satisfied: Permit.Value = 1 (startup enable), Protect.Value = 1 (interlock protection), and Intlock.Value = 1 (operational interlock).

Step-by-Step Implementation Procedure

  1. Analyze Block Status Online in CFC Test Mode:
    a. Open the CFC chart containing the MotL instance.
    b. Enter CFC Test Mode and monitor inputs:

    • ModLiOp.Value: Must be 1 (programmatic control enabled).
    • AutModLi.Value: Must be 1 (automatic mode requested).
    • ManModLi.Value: Must be 0 (ensure manual request is not active).
      c. Inspect block output AutAct.Value: If AutAct = 0 and ManAct = 1, the mode switch failed.

  2. Configure Level-Sensitive Mode Switching (Feature Bit 4):
    a. In CFC, open the Object Properties of MotL.
    b. Locate parameter Feature.
    c. Set Feature.Bit4 = 1 ('Switch to automatic mode via level-sensitive signal').
    d. When active, holding AutModLi = 1 continuously forces Automatic mode without requiring edge toggling.

  3. Structure Robust SFC Step Actions:
    a. Open the controlling SFC chart in the SFC Editor.
    b. In the target Step Properties, navigate to the 'Initialization' tab:

    • Set Chart\MotL.ModLiOp = 1
    • Set Chart\MotL.AutModLi = 1
      c. In the preceding Step or Step Termination tab, ensure reset actions clear conflicting commands:
    • Clear Chart\MotL.ManModLi = 0
      d. If keeping Feature.Bit4 = 0 (edge-triggered), ensure the step prior to the start step explicitly resets AutModLi = 0 to enable a fresh rising edge.

  4. Verify Interlock Permissives for Motor Starting:
    a. In Automatic mode, starting the motor requires asserting StartAut = 1.
    b. Check inputs Permit, Protect, and Intlock: verify all read 1 (healthy).
    c. If any interlock reads 0, inspect the connected upstream interlock block (Intlk04 / Intlk08) to resolve the field condition.

  5. Compile and Download Changes:
    a. Compile CFC and SFC charts with 'Changes only'.
    b. Download changes to the AS controller in RUN mode.

Verification

  1. Release and start the batch recipe in SIMATIC BATCH Control.
  2. When the batch sequence reaches the motor activation phase, monitor MotL in CFC test mode.
  3. Verify that AutAct.Value transitions to 1 (Automatic active) and ManAct.Value transitions to 0.
  4. Confirm that StartAut commands Start.Value = 1 and the motor contactor energizes.
  5. In WinCC OS, confirm that the motor faceplate displays 'Auto' mode and green running status.

Limitations and Operational Precautions

Setting Feature.Bit4 = 1 permanently forces automatic mode while AutModLi = 1, locking out manual faceplate intervention; ensure the SFC clears ModLiOp = 0 or resets AutModLi = 0 upon recipe completion to return control to operators.

Engineer FAQ

Why did ModLiOp = 1 and AutModLi = 1 fail to switch MotL to Auto?

Because by default (Feature.Bit4 = 0), AutModLi requires a rising edge (0 to 1). If AutModLi was already 1, no edge occurred and the switch was ignored.

What does Feature Bit 4 do on MotL?

Feature Bit 4 enables level-sensitive mode switching, allowing a continuous TRUE signal on AutModLi to hold the block in Automatic mode.

What is the difference between AutModLi and StartAut?

AutModLi commands the operating mode (Automatic vs Manual), whereas StartAut commands the motor to start running once Automatic mode is active.

Can an operator switch to Manual from the faceplate if ModLiOp = 1?

No. When ModLiOp = 1, faceplate mode buttons are locked out and control is granted exclusively to CFC/SFC program logic.

How do I return control to the operator after the batch finishes?

In the SFC recipe termination step, set ModLiOp = 0 and AutModLi = 0 so the faceplate buttons become active again.

Technical References

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Related Tags

  • MotL
  • SFC
  • SIMATIC BATCH
  • ModLiOp
  • AutModLi
  • Feature Bit 4
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