Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 97

Normal step (without attribute)
Normal step is a basic step used to comprise a block.
While this type of step is active, the transition following the step is always checked, and when the transition becomes TRUE,
the next step becomes active.
The output status of the action of a step, when a transition to the next step occurs, varies depending on the instruction used.
Item Description
When the OUT When a transition to the next step occurs and the
instruction is used relevant step becomes inactive, the output by using the
(Other than the OUT instruction turns off automatically.
OUT C instruction) Similarly, the timer also clears the current value and
turns off the contact.
However, the select statement of structured text
language or the output by using the OUT instruction
which is repeatedly using within the statement does not
turn off automatically.
When the OUT C If the execution condition of the counter in the action is
instruction is used already on when the transition becomes TRUE and
activate the step, the counter is incremented by 1.
When a transition to the next step occurs before reset
instructions of the counter is executed, the present
value of the counter and the ON state of the contact is
held even if the step becomes inactive.
To reset the counter, use the RST instruction in another
step.
When the SET, If a transition to the next step occurs and the step
basic, or application becomes inactive, the ON state or the data stored in the
instruction is used device/label is held.
To turn off the ON device/label or clear the data stored
in the device/label, use the RST instruction in another
step.
When the PLS Even when the contact of the execution condition is
instruction or always on, the instruction is executed every time the
instructions step changes from inactive to active.
executed at the
rising edge is used
■ Step without action
A step without an action can also be used as a waiting step.
• While a step is active, the transition is always checked and, when the transition becomes TRUE, the next step becomes
active.
• This type of step works as a normal step if an action is added to it.
Example
X1
(1)
(2)
When the transition (2) becomes TRUE while Y0 is turned on by using the
OUT instruction triggered by the action of step (1), Y0 is automatically turned
off.
(1)
(2)
X10
(3)
If X10 is already on while step (1) is active, counter C0 counts once when
execution proceeds to step (3) after the transition (2) becomes TRUE.
X2
(1)
(3)
(4)
When Y0 is turned on by using the SET instruction triggered by the action in
step (1), the ON state will be held even when the transition (3) becomes
TRUE and a transition to step (4) occurs.
(1)
ON
(2)
Even when the contact of the execution condition is on (1), the PLS instruction
is executed every time the step (2) becomes active.
Y0
OUT C0 K10
SET Y0
(2)
PLS Y0
8 SFC PROGRAM
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8.2 Structure
8