
10.STEP SEQUENCE FUNCTION B-63983EN/02
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(3) Transition
Pn
A transition denotes the transition conditions. When these
evaluate true, the step of the corresponding state changes from
the inactive to active state or vice the reverse. Specify the P
address (Pn), which indicates a subprogram describing the
transition conditions in detail.
As shown in Fig. 10.2.1(c), step S2 changes its state from
inactive to active when the conditions described in transition P10
evaluate true, while step S2 changes its state from active to
inactive when the conditions described in transition P20 evaluate
true.
Fig. 10.2.1(c) Transition of step state by the transition
Note that the step immediately before a transition must be active
in order to switch the next step from inactive to active when the
conditions specified in the transition evaluate true. As shown in
Fig. 10.2.1(d), step S3 does not change to the active state, even
when transition P20 evaluates true, if step S1 is active and step
S2 is inactive. An active state passes from a certain step to the
next step when the corresponding transition conditions evaluate
true, the execution of the step sequence program advancing one
step.
Executing step1 Executing step2 Executing step3
S1 (step 1) S1 (step 1) S1 (step 1)
P10 (Condition is true)
S2 (step2)
P20
P20 (Condition is true)
S3 (step3)
P10
S2 (step2)
S3 (step3)
P20
P10
S2 (step2)
S3 (step3)