Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 142

■ Precautions
• As a step for which the transition becomes TRUE at the first execution is deactivated in a single scan, the I/O refresh of coil
output is not reflected and therefore other programs cannot detect that the coil output is on. To reflect the I/O refresh, create
a program so that one step is executed in multiple scans.
• The actions of active steps in a block are executed simultaneously (within the same scan). For this reason, do not create
SFC programs which depend on the execution sequence of actions.
(1)
Continuous transition ON/OFF operation
There are two types of transitions in SFC program: "Continuous transition" and "No continuous transition".
The setting of the type (Continuous transition or No continuous transition) is determined by the settings of the continuous
transition bit of the SFC information device and SM323 (All-blocks continuous transition status).
Continuous SM323
transition bit
No setting Off
On
Off On or off
On On or off
The tact time can be shortened by setting "Continuous transition". This resolves the problem of waiting time
from when the transition becomes TRUE until the action of the transition destination step is executed.
However, when "Continuous transition" is set, the operations of the other blocks and sequence program may
become slower.
8 SFC PROGRAM
140
8.6 SFC Program Execution Order
(2)
(3)
Description
No continuous When the transition becomes TRUE, the action of the transition destination step is executed in the
transition next scan.
Continuous When the transition becomes TRUE, the action of the transition destination step is executed within
transition the same scan.
When the transitions of the steps become TRUE continuously, the actions are executed within the
same scan until the transition becomes FALSE or the end step is reached.
No continuous When the transition becomes TRUE, the action of the transition destination step is executed in the
transition next scan.
Continuous When the transition becomes TRUE, the action of the transition destination step is executed within
transition the same scan.
When the transitions of the steps become TRUE continuously, the actions are executed within the
same scan until the transition becomes FALSE or the end step is reached.
The execution sequence of actions (1), (2), and (3) are undefined.