Siemens SIMATIC FM 450-1 Manual page 19

Continuous If a counter reaches the upper limit when counting up, and if another count
Counting
pulse comes, the counter jumps to the lower count limit and starts to add the
count pulses again; so it continues to count continuously.
If a counter reaches the lower limit when counting down, and if another
count pulse comes, it jumps to the upper count limit and continues to count
down from there.
Figure 2-1
Single Counting In single counting, the counter starts at the load value. If a counter reaches
the upper count limit when counting up, and if another count pulse comes,
the counter jumps to the lower count limit and remains there even if further
count pulses come.
If a counter reaches the lower limit when counting down, and if another
count pulse comes, it jumps to the upper limit and remains there even if fur-
ther count pulses come.
Figure 2-2
FM 450-1 Counter Function Module
C79000-G7076-C450-01
www.gkbpx.com
Counter status
Upper count limit
Lower count limit
Continuous Counting in the Up Direction
Counter status
Upper count limit
Load value
Lower count limit
Single Counting in the Up Direction
How the FM 450-1 Counts
Time
Time
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