8 SFC PROGRAM
8.2 Structure
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8
Initial step
The initial step represents the beginning of each block. Only one initial step can be described in one block. (Page 73
Specifications) 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 the initial steps with step attributes
The attribute of SC (coil HOLD step) or R (reset step) can be added to the initial step. When the attribute is added, the
operations other than the operation that will be automatically activated at the start of the block are the same as those in other
steps. This step can also be used without an action.
Coil HOLD step [SC]
Coil HOLD step [SC] is a step that holds the outputs of a coil that has been turned on by the action even after the active state
transitions.
No operation in the action is performed after a transition becomes TRUE and the next step is activated. Therefore, the coil
output status will remain unchanged even if the input condition in the action is changed.
■Timing of when coil output turns off
The coil output holding ON state is turned off in the coil HOLD step [SC] after transition when:
• The end step of a block is executed (other than the case where SM327 is on).
• A block is forcibly terminated by the SFC control instruction (Ending a block).
• A step is reset by using the SFC control instruction (Ending a step).
• A reset step [R] for resetting the coil HOLD step [SC] becomes active.
• SM321 (Start/stop SFC program) is turned off.
• The coil is reset by the program.
• S999 is specified at a reset step [R] within a block.
Operation of active step Method
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 block 0 is started using the auto-start setting of block 0
Only the specified step is activated. When any of the initial steps is specified using the step control instruction of the SFC control instructions
Y10 (1) that has been turned on by the OUT instruction is not turned off and
remains on (3) even when the transition (2) becomes TRUE.
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