
3.CREATING AND EDITING SEQUENCE PROGRAMS B-63484EN/05
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Table 3.4.1
State Processing Sn.0
Active Running
The step is active.
The corresponding action program
(subprogram) is running.
1
Stopping
The step is shifting from running to stopped.
The corresponding action program
(subprogram) is executed only once. After this it
is stopped.
0
Inactive
Stopped
The step is inactive.
The corresponding action program
(subprogram) is not running.
0
NOTE
The state of a specified step can be read through a
contact; it cannot be written, however.
Sn.0 (where n represents a step number, which
can take a value from 1 to 1000)
Step numbers are used in a program so that
transition between steps can be controlled in detail.
Using step numbers makes it possible for any
subprogram to detect the state of any step.
However, the use of step numbers adversely
affects program transportability and ease of
understanding. Do not use step numbers
excessively.
Initial step
An initial step is a step that automatically becomes active when the
program starts running. Except for this point, the initial step behaves
in the same manner as ordinary steps. Control can be passed from a
usual step to the initial step again. In this case, the initial step behaves
in exactly the same manner as an ordinary step.
• A step number [Sn] necessary to control the execution and a
subprogram [Pm] that describes the actual processing are defined
for an initial step.
• All initial steps become active when no other step is running.
• Each block must have at least one initial step. It can have any
number of initial steps.
• If a block has no initial step, it is not executed even if called.
• Each initial step is always assigned a step number. A duplicate
step number cannot be used in a program.
• If there are initial steps in the middle of parallel branching, there
must be at least one initial step in each flow.