Configure Crossload and Synchronization Settings

You can limit which tasks or programs crossload and synchronize data after execution. In many applications, changes to this setting can reduce the overall impact to the task scan time by reducing the number of times data is crossloaded.

Standard Task Settings

You can improve standard task scan time by disabling data synchronization for a task. When data synchronization is disabled, no data is transferred to the secondary controller after the task executes, including the last program in its program list.
IMPORTANT: At least one standard user task in your application must have data synchronization enabled. The highest priority standard task with data synchronization enabled can achieve a seamless switchover.
Disabling data synchronization is useful for tasks that do not need to retain their state after a switchover.
IMPORTANT: We recommend that you do not disable data synchronization for tasks that use SSV instructions. If the task contains SSV instructions, the task can experience spikes in scan times while those instructions are synchronized.
Before disabling data synchronization for a task, consider the following implications:
  • No changes to standard tag values within the task are synchronized with the secondary controller:
    • No changes to program-scoped tags are directly synchronized.
    • Changes to controller-scoped tags are synchronized in another standard task’s sync point.
  • Avoid the following elements in tasks with data synchronization disabled:
    • Alarm instruction
    • Equipment phase
    • MSG instruction
    • Sequential function chart (SFC)
    IMPORTANT: When in a task with data synchronization disabled, an SFC requires a Reset SFC (SFR)/Pause SFC (SFP) following a switchover to function properly.
  • For a consistent production of outputs, output values are not transferred to the I/O module until another task with data synchronization enabled completes its scan.
  • If you choose to disable data synchronization for a task, the data synchronization setting for all programs under the task is ignored.
  • If a switchover occurs during a task with data synchronization disabled, the following occurs:
    • The new primary controller begins execution of the task starting with the first program in its program list. Depending on the application, programming may be required to make data on the new primary usable. See Program Logic to Run After a Switchover.
    • The task does not maintain its periodic execution rate through the switchover. When it is scheduled to run, it starts immediately and does not depend on the remaining time in its period. Going forward, the task resumes its periodic rate.
  • If a task with data synchronization disabled shares data with a task that synchronizes data, special logic may be required during the first scan. For example, copying controller-scoped tag values that are changed by a ‘sync-disabled’ task to or from standard tags that are mapped to safety tags should not be done during the first scan.
You can change the data synchronization setting for a standard task on the Configuration tab of the task properties. The setting can be modified only when offline.
Data Synchronization Setting for a Task
Synchronize redundancy data after execution checkbox
When you disable data synchronization for a task, the following warning appears to confirm the changes.
Disable Task Data Synchronization Warning
Disable Task Data Synchronization Warning
When you apply the changes, the 'Disable automatic processing to reduce task overhead' checkbox becomes enabled and the setting cannot be changed, even when offline, until the 'Synchronize redundancy data after execution' checkbox is selected.
IMPORTANT:
The Disable automatic processing to reduce task overhead setting must not be enabled for at least one frequently executed standard task.
Disable Automatic Output Processing
Disable Automatic Output Processing checkbox
You can monitor the data synchronization setting for a task by using the SynchronizeRedundancyDataDisabled attribute in a Get System Value (GSV) instruction.
Monitor Data Synchronization Setting
Monitor Data Synchronization Setting Attribute

Program Settings

If you reduce the number of crossload and synchronization points, the switchover time becomes longer as more programs must be rescanned after the switchover.
Synchronization is performed at the end of the last program in the program list of the task, regardless of the Synchronize Data after Execution setting for the program.
You can change the synchronization setting for a program on the Configuration tab of the program properties.
Data Synchronization Setting for a Program
Data Synchronization Setting for a Program

Default Settings

The default setting for standard tasks and programs in a redundancy project is for a crossload to occur at the end of each task and program execution. However, for an equipment phase, the default setting is that the crossload does not execute at the end of the phase.
Before you change the default crossload and synchronization settings, read the sections that follow so you have a complete understanding of the implications.
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