Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 438)

Spindles
Chapter 17
17-2
Important: On the 9/260 and 9/290 controls, if the auxiliary spindles are
programmed but have not been configured as active through AMP, these
errors are given as decode errors on any blocks that have the G12.2 or
G12.3 code:
“SPINDLE 2 NOT CONFIGURED” and/or
“SPINDLE 3 NOT CONFIGURED”
Spindle Speed (S-word)
Use the S-word to program the spindle speed for all configured spindles.
The common S-word can be applied per spindle by associating the S-word
in the same block with the spindle directional M-codes. See the section on
spindle direction for information about spindle directional M-codes. If no
directional M-code is programmed in the block with the S-word, then the
S-word is applied to the active controlling spindle. The S-word units
represent revolutions per minute (RPM).
CAUTION: The displayed S-word always shows the
controlling spindle’s programmed spindle speed. The display
of the S words for noncontrolling spindles must be handled by
some other display means. See the system installer’s
documentation for display capabilities of the active spindle
speed for noncontrolling spindles.