Siemens SIMATIC S7-1500 Function Manual page 42

Basics
3.14 Homing
Homing with digital input
The system checks the state of the digital input, as soon as the actual value of the axis or
encoder moves in the assigned homing direction.
When the homing mark is reached (setting of the digital input) in the specified homing
direction, the actual position of the technology object is set to the homing mark position.
Note
The digital inputs must be placed into the process image partition "PIP OB Servo".
The filter time of the digital inputs must be set smaller than the duration of the input signal at
the reference point switch.
See also
Homing SINAMICS drives with external zero marks (Page 396)
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S7-1500 Motion Control V13 Update 3
Function Manual, 07/2014, A5E03879256-AC