Initial Step - Mitsubishi Electric MELSEC-Q Series Programming Manual

Initial step

The initial step represents the beginning of a block. Up to 32 initial steps per block can be designated. When there are more
than one initial step, the coupling enabled is only a selective coupling. Execute the initial steps in the same way as executing
the steps other than the initial step.
Active steps at block START
When the block that has more than one initial step is started, the active steps change depending on the starting method as
described below.
■All initial steps become active.
• When a start is made using the block START step
• When a start is made using the block START instruction of the SFC control instructions
• When a forced start is made using the block START/END bit of the SFC information devices
■Only the specified step becomes active.
• When any of the initial steps is specified using the step control instruction of the SFC control instructions
Transition processing performed when multiple initial steps become active
If steps are selectively coupled in the block that has more than one active initial steps, the step immediately after the coupling
becomes active if any of the transition conditions immediately before the coupling is satisfied. In the above program example,
step 8 (S8) becomes active when any of transition conditions t4 to t7 is satisfied. When, after the step immediately after the
coupling (S8 in the above program example) becomes active, another transition condition immediately before the coupling
(any of t4 to t7 in the above program example) is satisfied, reactivation processing is performed as a follow-up function. The
processing, which will be performed when another transition condition is satisfied with the step immediately after coupling
being active, can be selected between STOP, WAIT and TRANSFER in the "Operation mode at transition to active step
(double step START)" in the block parameter setting of the SFC setting dialog box in the Tools menu. ( Page 127
Operation mode at transition to active step (double step START))
For the Basic model QCPU, Universal model QCPU, and LCPU, setting of "Operation mode at transition to
active step (double step START)" is not allowed. It operates in the default "TRANSFER" mode.
4 SFC PROGRAM CONFIGURATION
4.2 Steps
4
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