Siemens SINUMERIK 840D sl Function Manual page 97

Zero-mark monitoring
PROFIBUS drives with incremental encoders
Zero-mark monitoring is performed by the drive software.
PROFIBUS drives with absolute encoders
The drive software performs the monitoring function, while the plausibility check is carried
out in the NCK (as for SIMODRIVE 611D systems).
2.1.7 Limit switches-monitoring
Overview of the end stops and possible limit switch monitoring:
2.1.7.1 Hardware limit switches
Function
A hardware limit switch is normally installed at the end of the traversing range of a machine
axis. It serves to protect against accidental overtravelling of the maximum traversing range of
the machine axis while the machine axis is not yet referenced.
If the hardware limit switch is triggered, the PLC user program created by the machine
manufacturer sets the corresponding interface signal:
DB 31, ... DBX12.0 / 12.1 = 1 (Hardware limit switch minus / plus)
Basic logic functions: Axis monitoring, protection zones (A3)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.1 Axis monitoring
31