Siemens LOGO!, Manual

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LOGO! functions
4.4 Special functions list - SF
LOGO!
Manual, 04/2011, A5E03556174-01
203
Timing diagram
4
5
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2Q 2II
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Functional description
The internal counter increments (Dir = 0) or decrements (Dir = 1) by one count with every
positive edge at input Cnt.
You can use input R to reset the internal count value to the start value. As long as R = 1, the
output is also 0 and the pulses at input Cnt are not counted.
If retentivity is not set, output Q and the expired time are reset after a power failure.
Q is set or reset depending on the current value at Cnt and the set thresholds. See the
calculation rule below.
Calculation rule
● If the On threshold ≥ Off threshold, then:
Q = 1, if Cnt ≥ On
Q = 0, if Cnt < Off
● If the On threshold < Off threshold, then Q = 1, if On ≤ Cnt < Off.
Note
The system scans the counter limit value cyclically.
Thus, if the pulse frequency at the fast digital inputs I3, I4, I5 or I6 is faster than the cycle
time, the special function might not switch until after the specified limit value is exceeded.
Example: Up to 100 pulses per cycle can be counted; 900 pulses have been counted so
far. On = 950; Off = 10000. The output is set in the next cycle, after the value has
reached 1000. (The output would not be set at all if the value Off = 980).
View in programming mode (example):
2II
2Q
%5
2IIൺ%
2Q
%5
RU