Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 98

Initial step
The initial step represents the beginning of a block. Up to 32 initial steps per block can be described. ( Page 90
Specifications) When there are more than one initial step, the convergence enabled is only a selective convergence. Execute
the initial steps in the same way as executing other steps.
■ Active steps at block START
When multi-initial steps are used, the active steps change depending on the starting method as described below.
Operation of active step
All initial steps become active.
Only the specified step becomes active.
■ Transition processing performed when multi-initial steps become active
If steps are selectively connected in the block that has more than one active initial steps, the step immediately after the
convergence becomes active when any of the transition conditions immediately before the convergence is satisfied. In the
above program example, step 8 (S8) becomes active when any of transition conditions t4 to t7 is satisfied. When the step
immediately after the convergence (S8 in the above program example) becomes active and another transition condition
immediately before the convergence (any of t4 to t7 in the above program example) is satisfied, the step immediately after the
convergence becomes active again.
■ Operation of the initial steps with step attributes
An attribute of SC (coil HOLD step), SE (operation HOLD step (without transition check)), ST (operation HOLD step (with
transition check)), or R (reset step) can be added to the initial step. When an attribute is added, the operation other than
automatic activation when block is started is the same as the operation of other steps. This step can also be used without an
action.
8 SFC PROGRAM
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8.2 Structure
Method
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
When block 0 is started using the auto-start setting of block 0
When any of the initial steps is specified using the step control instruction of the SFC control
instructions