Siemens SIMATIC ET 200AL, System Manual

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Counting
4.3 Examples of counting
Digital input/Digital output module DIQ 16x24VDC/0.5A 8xM12 (6ES7143-5AH00-0BA0)
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Equipment Manual, 08/2021, A5E38688112-AD
Change counting direction via count input and stop counting (configuration method 2xCount)
The following section shows the behavior of the counter depending on the direction input at
the parameterization "Behavior DI: Counting direction" in combination with "Behavior when a
counting limit is exceeded: Stop counting".
If you have parameterized the digital input of a counter as a direction input, you can change
the counting direction via corresponding signals at this input.
Irrespective of the parameterization the counter always forward id the signal state "0" is set at
direction input or, respectively backward if the signal state is "1".
If you change the counting direction via a signal change at the direction input, the edge
detection (rising / falling edge) is also switched over.
The following figure shows an example of the behavior of the counter at a change in the
counting direction with the principle of stopping counting when a counting limit is exceeded.
Figure 4-16 Changing the counting direction and principle: Stop counting