Omron WS02-CXPC1-V8 - V8.1 REV 02-2009 Operation Manual page 65

Elements of SFC
•
The first operand time range for a step timer value instruction reading varies,
according to the time unit of the specified step timer, as follows.
• Actions with the action qualifier D, DS, or L are executed in synchronization with
the step timer. Caution should therefore be exercised when making changes to the
step timer of a step, which has those action qualifiers in its actions.
•
When the step becomes inactive, the step timer is stopped, and the elapsed time
data is saved. The step timer is reset when the step becomes active again.
•
When the step timer value reaches the upper limit, the timer will stop and maintain
the maximum value.
For detailed specifications of step control instructions, refer to Appendix A –
Specifications for Step Control Instructions.
Precautions on Subcharts
Executing the SA Step Control Instruction for a Subchart Step
When the SA step control instruction is executed for a subchart step, that subchart step
will become active, and the subchart will operate from the entry step.
Executing the SE Step Control Instruction for a Subchart Step
When the SE step control instruction is executed for a subchart step, that subchart step
will become inactive, and the subchart's operation will stop. (Active steps in the
subchart will become inactive.)
Using the SA and SE Step Control Instructions in a Subchart Step
The SA and SE Step Control Instructions cannot be used for a step in the same
subchart.
Note: SFC operation is different in the CV-series PLCs. In the CV-series PLCs, subchart steps
Operation When Multiple Subchart Steps Calling the Same Subchart Are
Active
• When a given subchart step is active, another subchart step calling the same
subchart can become active by a status transition or execution of the SA instruction
(see note). In this case, the subchart's current execution status will not change.
Execution of the subchart for any other subchart steps will standby until the subchart
step that first called the subchart becomes inactive.
• If the subchart step for which the subchart is currently being executed changes to
inactive status or the subchart step is deactivated with the SE instruction, the
subchart will be executed again from the entry step for any other subchart step that
was in standby status.
• If a subchart is currently being executed for one subchart step and another subchart
step calling the same subchart changes to inactive status or the subchart is
deactivated with the SE instruction, the subchart execution will continue as long as
the subchart step for which the subchart is currently being executed is still active.
Note: SFC operation is different in the CV-series PLCs.
• When multiple subchart steps are in standby status, the subchart that is executed
next is determined by the order in which the subchart steps are registered.
The execution order can be confirmed in the Action Used List Dialog Box. Refer to
Checking Action Usage under 2-3-3 Action Blocks.
• 100 milliseconds
• 1 second
• 100 milliseconds 0 to 6553.5 seconds
• 1 second 0 to 65535 seconds
can be used in instruction operands.
In the CV-series PLCs, if a given subchart step is active, another subchart step calling
the same subchart cannot become active by a status transition or execution of a step
control instruction. In this case, execution of the previous step continues, and the step
goes into standby status.
Section 2-3
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