Siemens SINUMERIK 840Di sl Programming Manual page 305

One of the spindles is defined in machine data as the master spindle. Special functions apply
to this spindle, such as thread cutting, tapping, revolutional feed, dwell time. The numbers
must be specified with the speed and the direction of rotation/spindle stop for the other
spindles, e.g., for a second spindle and actuated tool.
Example:
N10 S300 M3 S2=780 M2=4
Deactivate SETMS
By issuing SETMS without spindle parameter you can switchback to the master spindle
defined in the machine data.
Programmable switchover of master spindle, SETMS(n)
You can define any spindle as the master spindle with a command in the NC program.
Example:
N10 SETMS (2)
Note
The speed specified with S and M3, M4, M5 now apply.
Fundamentals
Programming Manual, 11/2006, 6FC5398-1BP10-2BA0
7.10 Spindle speed (S), direction of spindle rotation (M3, M4, M5)
;Master spindle 300 rpm, U/min, clockwise,
;2nd spindle 780 rpm, counterclockwise
;SETMS must be located in a separate block,
;spindle 2 is now the master spindle
Feedrate Control and Spindle Motion
305