Operation Hold Step (With Transition Check) - Mitsubishi Electric MELSEC-Q Series Programming Manual

Operation HOLD step (with transition check)

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.
Coil switched ON by the OUT instruction when the transition condition is satisfied
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.
Transition condition check after the next step becomes active
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.
• 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.
• 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  Page 127
Operation mode at transition to active step (double step START) for the parameter setting and the
processing performed for each setting.
• 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.
Timing when an operation HOLD step becomes inactive
An operation HOLD step (with transition check) becomes inactive when any of the following occur:
• When the end step of the corresponding block is executed.
• When an SFC control instruction (rBLm) designates a forced END at the block in question.
• When an SFC control instruction (rBLm\Sn, rSn) designates a reset at the block in question.
• When a reset occurs at the device designated as the SFC information register's block START/END device.
• When a reset step for resetting the step in question becomes active.
• When "S999" is designated at the reset step in the same block.
• When the SFC START/STOP command (SM321) is switched OFF.
4 SFC PROGRAM CONFIGURATION
4.2 Steps
4
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