Dummy Step; Coil Hold Step - Mitsubishi MELSEC-Q Series Programming Manual

4 SFC PROGRAM CONFIGURATION

4.2.3 Dummy step

A dummy step is a waiting step, etc., which contains no operation output program.
(1) The transition condition following the corresponding step is always checked during execution
of a dummy step, and execution proceeds to the next step when the transition condition is
satisfied.
(2) The dummy step changes to a step (without step attribute, indication:
output program is created.

4.2.4 Coil HOLD step

A coil HOLD step is a step where the coil output status is maintained in the transition to the next
step. (The coil output is switched ON by the OUT instruction when the transition condition is
satisfied.)
(1) During normal SFC program operation, the coil ON status (switched ON by OUT instruction
when transition condition is satisfied) is automatically switched OFF before proceeding to the
next step.
By designating an operation output step as a "coil HOLD step", the coil ON status will remain
in effect when proceeding to the next step.
[When designated as a coil HOLD step]
1) When step n is executed
SC
2) When a transition to step (n+1) occurs
SC
• At a designated coil HOLD step, "Y10"
(switched ON by OUT instruction) will
remain ON even when the transition
condition is satisfied.
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SC
When X1 turns ON,
Y10 turns ON.
X1
n
(ON)
Y10
n+1
Remains ON if
transition to step
(n+1) occurs.
X1
n
(ON)
Y10
n+1
(ON)
[When not designated as a coil HOLD step]
1) When step n is executed
Y10
(ON)
2) When a transition to step (n+1) occurs
Y10
(ON)
• At steps not designated as coil HOLD steps,
"Y10" (switched ON by OUT instruction) is
automatically switched OFF when the
transition condition is satisfied.
) when an operation
When X1 turns ON,
Y10 turns ON.
X1
n
(ON)
Y10
n+1
Y10 turns OFF when
transition to step
(n+1) occurs.
X1
n
(ON)
(OFF)
Y10
n+1
(OFF)
Y10
(ON)
Y10
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