Siemens Simatic S7-200 System Manual page 188

S7-200 Programmable Controller System Manual
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
6
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.
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State M
Divergence of a Control Stream
Network 1
LSCR
Network 2
LD
A
SCRT
SCRT
Network 3
SCRE
State L
Transition Condition
State N
//Beginning of State L control region.
S3.4
M2.3
I2.1
S3.5 //Transition to State M
S6.5 //Transition to State N
//End of the State region for State L.