Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 100

■ Operation when the block is paused or restarted
Operation when the block is paused or restart depends on the combination of SM325 (Output mode at block stop), block stop
mode bit setting of SFC information device, and step hold status. ( Page 133 Operation when the block is paused or
restarted)
Operation HOLD step (with transition check) [ST]
Operation HOLD step (with transition check) [ST] is a step which continues the operation of the action even after the active
state transitions.
This step continues the operation in the action even after a transition becomes TRUE and the next step is activated.
Therefore, when the input condition changes, the coil status also changes.
Even after the transition becomes TRUE and the next step is activated the transition is checked repeatedly. When the
transition becomes TRUE again, the operation in the action is continued while activating the next step again.
(1) (3)
(2)
■ Deactivation timing
An operation HOLD step (with transition check) [ST] becomes inactive when:
• The end step of a block is executed.
• A block is forcibly terminated by using the RST instruction (Ending a block).
• A step is reset by using the RST instruction (Deactivating a step).
• The device specified as the block start/end bit of the SFC information devices is reset.
• A reset step [R] for resetting the operation HOLD step (with transition check) [ST] becomes active.
• SM321 (SFC program start/stop) is turned off.
• S999 is specified at a reset step [R] within a block.
■ Operation when the block is paused or restarted
Operation when the block is paused or restart depends on the combination of the SM325 (Output mode at block stop) status,
block stop mode bit setting of the SFC information device, and step hold status. ( Page 133 Operation when the block is
paused or restarted)
■ Precautions
• For the operation HOLD step (with transition check) [ST], the next step is activated every scan while the transition
immediate after the operation HOLD step becomes TRUE. To prevent transition every scan, use instructions executed on
the rising edge such as the PLS instruction for the transition.
(1)
(2)
• When SM328 (Clear processing mode when the sequence reaches the end step) is on, prevent the transition immediately
after the operation HOLD step (with transition check) [ST] from becoming always TRUE. Otherwise, the next step is kept
activating and holding no operation, therefore the block cannot be ended.
8 SFC PROGRAM
98
8.2 Structure
X0
X0
TRAN
When step (2) is activated, step (1) holds the operation.
The action (3) is kept executed the same as a normal active step while
Y10
the step holds the operation.
In this case, Y10 turns on or off accordingly as X0 turns on or off.
The transition is also checked and, when the becomes TRUE, the next
step becomes active.
By setting the start of rising edge pulse operation as the transition, step (1) is
activated during only one scan caused when X0 is turned on.
Even when step (2) is activated and becomes inactive, step (1) is not activated
unless X0 is turned off and on again.