Siemens SIMATIC S7-200 System Manual page 189

Divergence Control
In many applications, a single stream of sequential states must be split into two or more different
streams. When a control stream diverges into multiple streams, all outgoing streams must be
activated simultaneously. This is shown in Figure 6-32.
Figure 6-32 Divergence of a Control Stream
The divergence of control streams can be implemented in an SCR program by using multiple
SCRT instructions enabled by the same transition condition, as shown in the following example.
Example: Divergence of Control Streams
Convergence Control
A situation similar to divergence control arises when two or more streams of sequential states
must be merged into a single stream. When multiple streams merge into a single stream, they are
said to converge. When streams converge, all incoming streams must be complete before the
next state is executed. Figure 6-33 depicts the convergence of two control streams.
The convergence of control streams can be implemented in an SCR program by making the
transition from state L to state L' and by making the transition from state M to state M'. When both
SCR bits representing L' and M' are true, state N can the enabled as shown in the following
example.
State L
State M
Network 1
LSCR S3.4
Network 2
LD M2.3
A I2.1
SCRT S3.5
SCRT S6.5
Network 3
SCRE
S7-200 Instruction Set
Transition Condition
State N
//Beginning of State L control region.
//Transition to State M
//Transition to State N
//End of the State region for State L.
Chapter 6
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