8 SFC PROGRAM
8.2 Structure
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8
Block start step (without END check) [BS]
Block start step (without END check) [BS] is a step that activates the specified block.
When the transition becomes TRUE, the active state transitions to the next step.
The operation to be performed if multiple attempts to start one block are performed simultaneously or if an attempt to start an
already started block is performed depends on "Act at block Multi-Activated." (Page 100 Act at block Multi-Activated)
Only one block can be specified. To start multiple blocks simultaneously, use parallel branches and multiple block start steps.
■Precautions
An action cannot be created to the block start step (without END check) [BS].
End step
End step is a step that ends a block.
• When the active state transitions to the end step, and if there are no active steps other than steps that hold operations in
the block, all the HOLD steps that hold operations in the block are deactivated, and the block is ended.
• When a block contains any active steps other than steps that hold operations in a block, the following processing is
performed depending on the status of SM328 (Clear processing mode when the sequence reaches the END step).
• When the clear processing is performed, the coil outputs turned on by using the OUT instruction are all turned off. However,
for the coil outputs of the HOLD steps that hold operations, the following processing is performed depending on the status
of SM327 (Output mode at execution of the END step).
After this step starts block (BL1), only the transition (2)
is checked and, when the transition becomes TRUE,
execution proceeds to the next step without waiting for
the start destination block to end.
Status of SM328 Description
OFF (default) Clear processing is performed.
The active steps remaining in the block are all terminated forcibly to end the block.
ON Clear processing is not performed.
The block continues running in the state when the end step is reached and does not end.
Status of SM327 Description
OFF (default) All the outputs of the HOLD steps that hold operations are turned off.
ON All the outputs of the HOLD steps that hold operations are held.
The setting of SM327 is valid for only the coil HOLD step [SC] that holds operation. All the
outputs of the coil HOLD step [SC] that does not hold operation and the transition does not
become TRUE are turned off. Also, even when SM327 is on, the steps become inactive.
However, when a forced end is performed such as by the block end instruction, the coil
outputs of all steps are turned off.
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