Siemens SINUMERIK 840D sl Function Manual page 189

Number of valid fixed point positions
The number of fixed point positions entered in MD30600 $MA_FIX_POINT_POS that are
actually valid, can be defined using:
MD30610 $MA_NUM_FIX_POINT_POS = <number of valid fixed point positions>
Note
Exception: G75
For compatibility reasons, the following parameter assignment is also possible for G75:
MD30610 $MA_NUM_FIX_POINT_POS = 0 (no valid fixed point positions)
it is assumed that there are two valid fixed point positions in MD30600
$MA_FIX_POINT_POS[0] and [1].
Fixed point positions 1 and 2 can be activated via the NC/PLC interface, however they can
only be approached via G75.
Extended Functions
Function Manual, 10/2015, 6FC5397-1BP40-5BA3
H1: Manual and handwheel travel
4.9 Approaching a fixed point in JOG
189