Siemens simatic s7-400 FM 450-1, User Manual, Page: 21 / 130

This is how the FM 450-1 counts
2.1 Basics
Counter module FM 450-1
Manual, 02/2014, A5E03648739-02
21
Periodic counting
For periodic counting the respective counter starts from the load value. If when counting up
the counter reaches the high count limit and further count pulses come, then the counter
jumps to the load value and starts totalizing the count pulses.
Figure 2-3 Periodic 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 load value and then continues counting down from
there.