Siemens SIMATIC S7-200

Pulse Operated Switch
3.3 Edge detection
Getting Started - Advanced
Training Documents, 09/2007, A5E01469795B
25
3.3 Edge detection
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The moment of transition of a
contact (input, output ...) from
"open" to "closed" or from "false"
to "true" is referred to as the
rising or positive edge.
Correspondingly, the transition
from "closed" to "open" or from
"true" to "false" is referred to as
the falling or negative edge.
The two Bit Logic functions -|P|-
and -|N|- can detect rising and
falling edges.
In our example, we use the -|P|- function as follows:
RXWSXWVLJQDO
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3
D
D
V
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V
SRVLWLYHHGJH
SRVLWLYHHGJH
,QSXWVLJQDO
)RURQHVFDQF\FOHZHJHWDRUD
SRZHUIORZLQWKHODGGHUGLDJUDP
And this is what the
—|P|— function output
signal looks like.