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4 SFC PROGRAM CONFIGURATION
MELSEC-Q
4.2.6 Operation HOLD step (with transition check)
ST
An operation HOLD step (with transition check) is a step where the operation output processing of
the corresponding step continues after a transition to the next step.
When the transition condition is satisfied again at the corresponding step, transition processing to
the next step (reactivation) is executed.
(1) During normal SFC program operation, the coil ON status (switched ON by OUT instruction
when transition condition is satisfied) is automatically switched OFF before proceeding to the
next step.
When an operation output step is designated as an operation HOLD step (with transition
check), the corresponding step will remain active after a transition to the next step, and
operation output processing will continue.
(2) The transition condition will be checked after the transition condition is satisfied and the next
step is activated.
Hence, when the transition condition of the corresponding step is satisfied again, a transition to
the next step (subsequent transition) occurs to activate it.
At this time, the current step remains active.
(Transition is
executed again.)
Step which is active
due to the previous
transition condition
being satisfied
oY10
pX1
POINTS
(1) Convert the transition conditions into pulses.
If they are not pulsed, transition processing to the next step is performed every scan while
the condition is satisfied.
(2) When a double START occurs as the transition condition was satisfied with the transition
destination step being active, the processing changes depending on the parameter setting.
The Basic model QCPU does not allow the parameters to be selected.
It operates in the default "Transfer" mode.
Refer to Section 4.7.6 for the parameter setting and the processing performed for each
setting.
(3) The difference between the operation HOLD step (with transition check) and the operation
HOLD step (without transition check) is whether the next step will be activated or not as a
follow-up when the transition condition is satisfied again.
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