C135 PCS 7 (PCS7)
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Resolving Grayed-Out 'Load Schedule to Device' Option in SIMATIC PDM for Fieldbus Devices

Resolving Grayed-Out 'Load Schedule to Device' Option in SIMATIC PDM for Fieldbus Devices

In SIMATIC PDM V9.1, the 'Load schedule to device' option for Foundation Fieldbus (FF) devices is grayed out when the FF segment schedule has not been generated and compiled in the FF Link configuration, when PDM is not in the online communication state, or when the user lacks adequate SIMATIC Logon permissions. To resolve this, open the Compact FF Link / FF Link properties in HW Config, execute the macrocycle schedule calculation under 'Schedule Configuration', confirm that SIMATIC PDM establishes an online link to the Link Active Scheduler (LAS) device, and ensure your user role possesses device configuration rights.

Table of Contents

Executive Summary

Foundation Fieldbus (FF) technology relies on precise, deterministic communication scheduling where a designated Link Active Scheduler (LAS) arbitrates cyclic and acyclic communication macrocycles across all connected field transmitters and actuators. In SIMATIC PCS 7 utilizing SIMATIC PDM V9.1 and Compact FF Links (6ES7655-5FF00-0AB0), field engineers frequently attempt to transfer timing schedules to fieldbus devices, only to discover that the menu option 'Device' -> 'Load schedule to device' is disabled (grayed out). This article explains the Foundation Fieldbus scheduling architecture in PCS 7, diagnoses the prerequisites for schedule compilation, and provides a step-by-step restoration workflow.

Architectural and System Mechanics

Foundation Fieldbus Scheduling Mechanics in SIMATIC PDM:

  • Deterministic Macrocycle Architecture:
  • Unlike standard PROFIBUS or HART polling, FF function blocks (e.g., Analog Input, PID, Analog Output) execute synchronously within a fixed time window called the Macrocycle.
  • The Link Active Scheduler (LAS)—typically hosted within the Siemens Compact FF Link or backup master device—transfers scheduled tokens (Compel Data) to trigger execution.
  • Schedule Compilation Dependency:
  • SIMATIC PDM cannot download a schedule to a field device until the entire segment macrocycle has been compiled, scheduled, and validated in HW Config.
  • If any block execution time exceeds the macrocycle or if device tags are unmapped, the schedule compiler flags the configuration as uncompiled, graying out the download command in PDM.
  • Online Connection and Role Authentication:
  • The command requires an active online DPV1 communication session between PDM, the AS controller, and the physical FF bus segment.

Step-by-Step Engineering and Implementation Procedure

Step 1: Calculate and Compile the FF Segment Schedule in HW Config

  1. Open HW Config on the AS station.
  2. Locate the FF Link / Compact FF Link (6ES7655-5FF00-0AB0) on the PROFIBUS DP or PROFINET line.
  3. Double-click the FF Link master module to open Object Properties.
  4. Select the 'Fieldbus Configuration' or 'Schedule' tab.
  5. Click 'Calculate Schedule' / 'Compile'. Verify that the calculated macrocycle (e.g., 500ms or 1000ms) shows zero scheduling conflicts.
  6. Save and compile HW Config.

Step 2: Establish Online Connection to the Target Device in SIMATIC PDM

  1. In SIMATIC Manager Process Device Network View, expand the tree to the target Foundation Fieldbus device.
  2. Right-click the device and select 'Open Object' to launch SIMATIC PDM.
  3. In PDM, click the 'Online' button (or 'View' -> 'Online') to establish a live communication session.
  4. Verify that the communication status indicator in the bottom tray changes from gray to green ('Connected').

Step 3: Verify User Role in SIMATIC Logon

  1. Confirm that your logged-in user in SIMATIC Logon has 'Specialist' or 'Service' engineering rights.
  2. Read-only operator profiles have device configuration commands grayed out by design.

Step 4: Execute Load Schedule to Device

  1. With the schedule compiled and online link established, navigate to the PDM menu: 'Device' -> 'Load schedule to device'.
  2. The menu item is now active. Click it to download the compiled macrocycle timing parameters into the device's non-volatile memory.

Verification

To verify schedule download and segment health:
1. In PDM, inspect the device's LAS status; verify that the device acknowledges the active schedule.
2. Check the Compact FF Link diagnostic LEDs; verify that the 'ACT' and 'BUS' indicators show steady green operation.
3. In CFC, verify that the channel drivers (Pcs7AnIn) receiving values from this FF device show valid process quality (PV_Out.ST = 16#80).

Limitations and Operational Precautions

Operational precautions:
- Never download schedules to active FF segments on running production plants without putting control loops in Manual mode; updating the macrocycle temporarily disrupts cyclic token passing.
- Devices operating as backup Link Active Schedulers (LAS) must all receive matching schedule tables to prevent bus timing divergence if the primary master fails.
- Foundation Fieldbus segment length and terminator resistance (100 ohms at each bus end) must strictly meet FF-816 specifications.

Engineer FAQ

Q: Why is 'Load schedule to device' disabled in PDM?

A: The menu item is disabled when the FF segment schedule is uncompiled in HW Config, PDM is in offline mode, or the user lacks engineering privileges.

Q: What is a Compact FF Link in PCS 7?

A: It is a Siemens gateway module (MLFB 6ES7655-5FF00-0AB0) that connects Foundation Fieldbus H1 segments to PROFIBUS DP or PROFINET.

Q: What is an FF Macrocycle?

A: The periodic time interval during which all scheduled cyclic communication and function block executions occur on the fieldbus segment.

Q: Can standard HART devices use FF scheduling?

A: No. Deterministic scheduling is unique to Foundation Fieldbus and PROFIBUS PA; standard HART does not utilize macrocycles.

Q: Does downloading the schedule restart the field device?

A: Most FF devices execute a soft reset to reinitialize internal clock synchronization after receiving a new schedule.

Technical References

Related Articles

Related Tags

SIMATIC PDM, Foundation Fieldbus, Compact FF Link, Fieldbus Scheduling, Macrocycle

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