Siemens simatic s7-400 FM 450-1, User Manual, Page: 95 / 130

Encoder signals and their evaluation
9.5 Signal evaluation
Counter module FM 450-1
Manual, 02/2014, A5E03648739-02
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9.3 5-V differential signals
Count signals of 5-V incremental encoders
RS422 signals returned by the 5-V incremental encoder to the module:
● A and /A
● B and /B
● N and /N
The signals /A, /B and /N are the inverted signals of A, B and N. Signals A and B are phase-
shifted by 90°.
The tracks A and B of 5-V incremental encoders are used for counting. Track N is used to
initialize the counter with the load value, if programmed accordingly.
Encoders featuring these six signals are symmetrical encoders.
The diagram shows the time profile of the encoder signals:
Figure 9-1 Signals of the 5-V incremental encoder
The module detects the count direction by evaluating the ratio of signals A and B. The
diagrams in the chapter "Signal evaluation (Page 100)" show which edges of signals A and B
are counted in down or up direction.
Changing the count direction
You can change the count direction using the "Count direction normal" and "Count direction
inverted" parameters without having to modify the wiring.