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S7-GRAPH for S7 300/400 Programming Sequential Control Systems
1-2 C79000-G7076-C526-01
The Blocks of a Sequential Control System
A sequential control system controls the process in a fixed order dependent on
certain conditions.
The complexity of the sequential control system depends on the automation task.
However, even the simplest system requires at least the three following blocks:
• A STEP 7 block (1) in which the S7-Graph FB (function block) is called. This
block can be an organization block (OB), a function (FC), or another FB.
• An S7-Graph FB (2) that describes the individual subtasks and
interdependencies of the sequential control system. These subtasks (steps) and
interdependencies (transitions) can be organized in one or more sequencers.
• An instance DB (3) that contains data and parameters of the sequential control
system. The instance DB is assigned to the S7-Graph FB and can be created
automatically by the system.
OB/FB/FC
FC70/71/72
S2
S1
Comments for...
FB i
(1)
CALL FBi
DBi
INIT_SQ:=
(2) (3)
DB i
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