Siemens SINUMERIK 840D sl Programming Manual page 555

System variables
Current coupling status following spindle
The current coupling status of the following spindle can be read in the NC parts program with
the following axial system variable:
$AA_COUP_ACT[FS]
FS = axis name of the following spindle with spindle number, e.g., S2.
The value read has the following significance for the following spindle:
0: No coupling active
4: Synchronous spindle coupling active
Current angular offset
The setpoint of the current position offset of the FS to the LS can be read in the parts
program with the following axial system variable:
$AA_COUP_OFFS[S2]
The actual value for the current position offset can be read with:
$VA_COUP_OFFS[S2]
FS = axis name of the following spindle with spindle number, e.g., S2.
Note
When the controller has been disabled and subsequently re-enabled during active coupling
and follow-up mode, the position offset when the controller is re-enabled is different to the
original programmed value. In this case, the new position offset can be read and, if
necessary, corrected in the NC parts program.
Job planning
Programming Manual, 03/2006 Edition, 6FC5398-2BP10-1BA0
Additional functions
13.5 Synchronous spindle
13-23