Siemens SIMATIC S7 System Manual page 369

When the hardware limit switches are approached, the axis brakes to a standstill at the
configured emergency deceleration. The specified emergency deceleration must be
sufficient to reliably stop the axis before the mechanical stop. The following diagram
presents the behavior of the axis after it approaches the hardware limit switches.
①
②
A
B
C
D
E
F
Software limit switches
Software limit switches limit the "working range" of the axis. They should fall inside the
hardware limit switches relative to the travel range. Because the positions of the software
limit switches can be set flexibly, the working range of the axis can be restricted on an
individual basis depending on the current traversing profile. In contrast to hardware limit
switches, software limit switches are implemented exclusively by means of the software and
do not require their own switching elements.
If software limit switches are activated, an active motion is stopped at the position of the
software limit switch. The axis is braked at the configured deceleration. The following
diagram presents the behavior of the axis until it reaches the software limit switches.
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05
The axis brakes to a standstill at the configured emergency decleration.
Range in which the hardware limit switches signal the stats "approached".
[Velocity]
Allowed travel range
Distance
Mechanical stop
Lower hardware limit switch
Upper hardware limit switch
102BTechnology instructions
9.3 Basic motion control
369