Siemens SINUMERIK 840DE Programming Manual page 265

Example of positioning spindle with negative direction of rotation
Position spindle 2 at 250° in negative direction of rotation.
N10 SPOSA[2]=ACN(250)
Example of positioning spindles for position-controlled axis operation
...
N10 M3 S500
...
N90 SPOS[2]=0 or
M2=70
N100 X50 C180
N110 Z20 SPOS[2]=90
Fundamentals
Programming Manual, 10.2004 Edition, 6FC5 298-7AB00-0BP1
7.4 Positioning spindles (position-controlled axis operation) (SPOS, M19 and SPOSA)
;Position control on, spindle 2 positioned to 0, axis mode
;can be used in the next block.
;Spindle 2 is switched to axis mode
;Spindle 2 (C axis) is traversed with linear interpolation
;synchronous to X.
;Spindle 2 is positioned to 90 degrees.
;The spindle decelerates if necessary and accelerates
in the ;opposite direction to the positioning
;movement
Feedrate Control and Spindle Motion
7-15