Omron SYSMAC CX-Programmer 8.1, Руководство по эксплуатации

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Basic SFC Execution Cycle Section 2-2
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2-2 Basic SFC Execution Cycle
The following processing is performed in the SFC execution cycle as 1 unit for all active
steps. No processing is performed for inactive steps.
Action execution judgment
Action execution
Transition evaluation
Step transition processing
I/O refreshing
Cycle
Subchart processing
z Action execution
judgment
The results of the previous cycle’s step transition processing is received, and the AQ
(action qualifier) is read to determine whether or not the all of actions will be executed.
When a Boolean bit is specified in the action, the action is executed based on the result of
the action execution judgment. When multiple Boolean bits are specified in a single step,
they are executed in the order (from top to bottom) that they appear in the action block.
If active status has changed since the previous cycle, final scan processing (see note) is
performed for any action programs in steps that have changed to inactive status.
Note: Refer
to 1-5-2 Action Program Precautions for information on the final scan
operation.
z Action execution
When a step is active, the action programs written in the step are executed in the following
order, including actions in subcharts, based on the result of the action execution judgment.
• First, all actions for which Boolean variables are specified are executed according to
the action execution judgment. Then action programs are executed. For information on
the execution order of action programs, refer to
1-5-2 Action Program Precautions .
•
When the same action program is specified in two or more steps that are active at the
same time, that action program will be executed just once in a cycle.
z
Transition
evaluation
The transition conditions of active steps are evaluated. The transition program connected
after the active step is executed at this time.
z Step transition
processing
The current step is switched to inactive status and the next step is switched to active
status if the transition evaluation determined to move to the next step.
Note 1: The status is switched even if the next step is active (see note 2). If you do not
want the status to switch, add a transition condition that checks whether or not
the next step is active.
Note 2: SFC operation is different in the CV-series PLCs. In the CV-series PLCs, the
status is not switched if the next step is active.
z Subchart
processing
The subchart is executed if the subchart step is active. Subcharts are processed in the
following order:
1. Subchart initialization
2. Transition evaluations inside the subchart
3. Step transition processing inside the subchart
4. Processing to return from the subchart
Note: Actions inside a subchart are executed at the same timing as previously
described in Action Execution. If more than one subchart is active at the same
time, the subcharts are executed from top down in the order the subcharts are
arranged in the workspace.