Siemens simatic s7-400 FM 450-1, User Manual, Page: 20 / 130

This is how the FM 450-1 counts
2.2 Gate functions
Counter module FM 450-1
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Manual, 02/2014, A5E03648739-02
Continuous counting
If when counting in the up direction a counter has reached the high count limit and a further
count pulse comes, then the counter jumps to the low count limit and begins to total the
count pulses; thus, it counts continuously.
Figure 2-1 Continuous counting in the up direction
If when counting in the down direction a counter has reached the low count limit and a
further count pulse comes, then it jumps to the high count limit and then goes on counting
down from there.
Single counting
For single counting the counter starts from the load value. If when counting up a counter has
reached the high count limit and a further count pulse comes, then the counter jumps to the
low count limit and comes to a halt even if further count pulses come.
Figure 2-2 Single counting in the up direction
If when counting down a counter has reached the low count limit and a further count pulse
comes, then the counter jumps to the high count limit and comes to a halt even if further
count pulses come.