Siemens SIMATIC S5 Manual page 104

Synchronization yes:
In this case, the reference point is only located after the axis has left the precontact
and the excitation pattern counter has reached zero.
Note
single steps, the reference point approach is aborted and the error message "FBB
(59) reference cam switch defective".
Limit switch
v
V2
o
- VI
- V2
- V3
VI: Single step (25 Hz)
V2: Start-stop frequency
V3: Reference speed
Fig. 4/7 Reference point approach with reversal at the limit switch
Special cases with reference point approach
Depending on the position of the drive before the reference point approach is executed, there
are three special situations which affect the sequence of movement. These can be seen in the fol-
lowing diagrams. In the opposite approach direction, these movements are reversed.
Description of the Individual Operating Modes
3 0 1 2 3 0 1 2 3
: Precontact
Reference direction
Excitation pattern number
Limit
1) Reference point with synchronization
2) Reference point without synchronization
s
s
switch
4-11