Siemens SINUMERIK 840D sl Function Manual page 690

Software cams, position switching signals (N3)
9.2 Cam signals and cam positions
Figure 9-3
The signal change of the minus cam makes it possible to detect traversal of the cam even if
the cam range is set so small that the PLC cannot detect it reliably.
Both cam signals can be output to the PLC and to the NCK I/Os. Separate output of the plus
and minus cam signals makes it easy to detect whether the axis is within or outside the plus
or minus cam range.
If this condition (plus cam - minus cam < 180°) is not fulfilled or if the minus cam is set to a
greater value than the plus cam, then the response of the plus cam signal is inverted. The
response of the minus cam signal remains unchanged.
Figure 9-4 Software cams for modulo rotary axis (plus cam - minus cam > 180 degrees)
690
Software cams for modulo rotary axis (plus cam - minus cam < 180°)
Function Manual, 01/2008, 6FC5397-1BP10-3BA0
Extended Functions