Siemens SIMATIC S7-300 Manual page 258

Description of Functions
9.9 Software limit switches
Overview
To limit the working range, entries in the machine data (MD21 and MD22)
specify the start and stop limit switches. These limit switches are active at
synchronization of the axis.
If the limit switches are not needed, values lying outside the possible working
range should be entered in the machine data (MD21 and M22), or monitoring
should be switched off via the user program.
Warning
!
The software limit switches do not replace the hardware limit switches for
EMERGENCY STOP responses.
Effect of software
"Jogging mode"
limit switches in
At the limit switch the traveling movement is stopped in the limit-switch
modes
position, and an error is signaled.
"Control mode"
If the actual value is beyond the end position, the traveling movement is
stopped and an error is signaled. The limit-switch position is overshot by the
amount of the necessary deceleration distance.
"Reference-point approach" mode
No effect.
"Incremental relative", "MDI", "Automatic mode"
Movement is stopped, or not even started, as soon as read-in of the set posi-
tion reveals that the position lies outside the working range. An error is sig-
naled.
The following special cases exist:
Effect of software If the actual value is beyond the end position, an error is signaled.
limit switches in
tracking mode
Response after
Leaving end position or traveling into working range after error
error
1. Acknowledge the error message!
2. Travel to the working range with the "Jogging", "Control", "Incremental
9-82
Continuous travel (–) for set actual value on–the–fly (G88 see Chapter
10)
Continuous travel (+) for set actual value on–the–fly (G89 see Chapter
10)
Relative" or "MDI" mode.
FM 354 Servo Drive Positioning Module