Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 126

Step transition bit
This bit is a device or label to check whether the transition of the step being executed becomes TRUE.
This bit turns on when the transition to the next step becomes TRUE after execution of the action of each step.
A step transition bit which is on is automatically turned off when processing of the specified block is performed again.
Ex.
M1 is specified in the step transition bit of Block0
Block0
(1)
(2)
(3)
(4)
(5)
(6)
If the continuous transition bit is turned on and set to "Continuous transition", the step transition bit will remain on during the
action of the next step after the transition becomes TRUE. It will also remain on following the execution of multiple steps, even
if the transition becomes FALSE. In these cases, the step transition bit will be turned off when the specified block is executed
in the next scan.
1 scan
M1
(1)
(4)=OFF
(2)=ON
When multiple active steps exist in the block, the step transition bit turns on when one of the transition becomes TRUE.
■ Precautions
• When the end step is executed, the step transition bit of the block is turned on. The step transition bit remains on until the
block is reactivated next.
• The step transition bit is not turned off when the SFC program starts or ends.
8 SFC PROGRAM
124
8.4 SFC Information Devices
1 scan 1 scan
M1
(1) (3)
(2)=ON (4)=OFF
If transition (2) becomes TRUE after execution of step (1), M1 is turned on.
Even if transition (4) does not become TRUE, M1 stays on.
M1 is turned off at the time of Block0 processing in the next scan.
If transition (2) becomes TRUE after execution of step
(1), M1 is on during execution of another block.
M1 is turned off at the time of Block0 processing in the
next scan.
If transition (4) does not become TRUE after execution
of step (3), M1 stays off.
If transition (4) becomes TRUE, M1 is on during
execution of another block.
If transition (6) does not become TRUE after execution
1 scan of step (5), M1 stays off.
(5)
(4)=ON (6)=OFF