Siemens simatic s7-400 FM 450-1, User Manual, Page: 19 / 130

Counter module FM 450-1
Manual, 02/2014, A5E03648739-02
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This is how the FM 450-1 counts
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2.1 Basics
What is counting?
Counting refers to the recording and totaling of events. In the case of the FM 450-1 function
module encoder signals are captured and evaluated accordingly.
Count range, count limits
The FM 450-1 can count both forwards and backwards. When you select the count range,
you determine the limits between which the FM 450-1 can count.
Count range Low count limit High count limit
Count range 1:
0 to +32 bit
0 +4 294 967 295
Count range 2:
-31 to +31 bit
-2 147 483 648 +2 147 483 647
Load value
You can lay down an initial value for each of the two FM 450-1 counters from which the
counting is to begin. This initial value is the load value. You can specify any value within the
count limits for the load value.
Comparison values
You can use two digital outputs on the module for each counter in order to trigger reactions
in a process at a certain counter reading, independently of the CPU. You store two
comparison values for each counter on the FM 450-1. If the counter reading reaches one of
the two comparison values, the digital output assigned belonging to the comparison value is
set and/or a Hardware interrupt is generated.
Operating modes
You can count rectangular pulses in three different ways with the FM 450-1:
● Continuous counting, with or without gate function
● Single counting with hardware or software gate
● Periodic counting with hardware or software gate
The differences manifest themselves in the way the FM 450-1 behaves when a counter
reaches a count limit.