
B-66234EN/05 3.CREATING AND EDITING SEQUENCE PROGRAMS
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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.
Transition
A transition represents a condition under which transition occurs from
one step to another.
• There must be only one transition between steps.
• The transition of processing from one step to another is carried
out as described below:
• When a signal becomes on in a transition, its state is held even
after state transition occurs. So, if you do not want to maintain
the state, you must turn off the signal, using another subprogram.
When S1 is running, only S1 and P101 are
processed. The other steps or transitions are not
executed. Even if P102 is satisfied, it is invalid
unless S2 is running.
Transition from S1 to S2 can occur if P101 is
satisfied. When P101 is satisfied, S1 ends
regardless of the state of S1, allowing S2 to start.