Hardware And Software Limit Switches For Motion Control - Siemens SIMATIC S7 System Manual

102BTechnology instructions
9.3 Basic motion control
Drive interface
For motion control, you can optionally configure a drive interface for "Drive enabled" and
"Drive ready". When using the drive interface, the digital output for the drive enable and the
digital input for "drive ready" can be freely selected.
Note
The firmware will take control via the corresponding pulse and direction outputs if the PTO
(Pulse Train Output) has been selected and assigned to an axis.
With this takeover of the control function, the connection between the process image and I/O
output is also disconnected. While the user has the possibility of writing the process image of
pulse and direction outputs via the user program or watch table, this is never transferred to
the I/O output. Accordingly, it is also not possible to monitor the I/O output via the user
program or watch table. The information read merely reflects the value of the process image
and does not match the actual status of the I/O output in any respect.
For all other CPU outputs that are not used permanently by the CPU firmware, the status of
the I/O output can be controlled or monitored via the process image, as usual.
9.3.3.2

Hardware and software limit switches for motion control

Use the hardware and software limit switches to limit the "allowed travel range" and the
"working range" of your axis.
①
②
③
Hardware and software limit switches must be activated prior to use in the configuration or in
the user program. Software limit switches are only active after homing the axis.
Hardware limit switches
Hardware limit switches determine the maximum travel range of the axis. Hardware limit
switches are physical switching elements that must be connected to interrupt-capable inputs
of the CPU. Use only hardware limit switches that remain permanently switched after being
approached. This switching status may only be revoked after a return to the allowed travel
range.
368
Mechanical stop
Lower and upper hardware limits
Lower and upper software limits
A Allowed travel range for the axis
B Working range of the axis
C Distance
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05