
2. STEP SEQUENCE BASICS
B–61863E/15
STEP SEQUENCE FUNCTION
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(1) Step
Sn
(Pm)
A step indicates a process, which is the basic processing unit in a step
sequence program. In a step, specify the S address (Sn), which is a
step number, and P address (Pm), which indicates a subprogram
(action program) specifying the details of processing in each step.
(2) Step state transition
When a step sequence program is executed, the process proceeds as
program processing advances, the state of each step changs
accordingly. Each step can assume any of the logical states listed in
Table 2.1, its state changes as shown in Fig. 2.1 (b). Activation refers
to the changing of a step from the inactive state to the active state.
Inactivation refers to the changing of a step from the active state to
the inactive state.
Table 2.1 Step state
State
Processing Display
Active Execution Activated step.
The action program (subprogram) is being
executed.
Sn
Inactive Transition
to halt
Transition from execution to halt.
The action program (subprogram) is executed
once only, then the step automatically transits to
halt.
Halt Not activated state.
The action program (subprogram) has not yet
been executed.
Sn
Inactivate (halt status)
Activate (active status)
Inactivate (transition to halt)
Fig. 2.1 (b) Step state transition