Omron WS02-CXPC1-V8 - V8.1 REV 02-2009 Operation Manual page 62

Elements of SFC
Subchart
Step
A subchart is called up by a subchart step. Its execution begins at the subchart entry
terminal, and returns to the main process flow at the subchart return terminal.
• There is no limit on the number of subchart steps used within an SFC chart.
• If the transition conditions (for the downside transition) are met while a subchart step
is active, the active status is not transferred to the next subchart step until the SFC
within the subchart reaches its return step.
• The processing of a subchart always begins at the subchart entry terminal ( ) and
ends at the subchart return terminal ( ).
• When the return step becomes active, it will remain active until the active status is
transferred for the parent subchart.
• Each subchart requires one entry step and one or more return steps. There is no limit
on the number of return steps within a subchart.
• A subchart can call up another subchart.
There is no limit on the subchart layers.
• When the return step becomes active and the subchart is terminated, all other active
steps within the subchart are simultaneously terminated.
• A subchart step does not hold any action.
• A single subchart can be called up by multiple subchart steps. When two subchart
steps attempt to call up the same subchart, however, the latter caller must wait until
subchart execution is completed for the former caller.
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Step 10
Trans1
Step 11
Subchart 1
Trans2
Step 12
Subchart
Entry Terminal
Entry Step
Step 1
FALSE
Step 2
FALSE
Return Step
Step 3
Subchart
Return Terminal
Section 2-3
Subchart