Siemens SINUMERIK 840D sl Programming Manual page 215

The control needs the working plane parameter (G17 to G19) to calculate the direction of
rotation for the circle (G2 is clockwise or G3 is counter-clockwise).
It is advisable to specify the working plane generally.
Exception:
You can also machine circles outside the selected working plane (not with arc angle and helix
parameters). In this case, the axis addresses that you specify as an end point determine the
circle plane.
Programmed feedrate
FGROUP can be used to specify which axes are to be traversed with a programmed feedrate.
For more information please refer to the Path behavior section.
Fundamentals
Programming Manual, 09/2011, 6FC5398-1BP40-2BA0
Motion commands
9.6 Circular interpolation
215