Siemens SINUMERIK 840D sl Function Manual page 1281

For G70, G71 and when writing from an external (HMI), the setting in the machine data:
MD10240 $MN_SCALING_SYSTEM_IS_METRIC
determines the interpretation of the written values.
For further explanations regarding the measuring system (metric/inch) see Section "G2:
Velocities, setpoint / actual value systems, closed-loop control (Page 317)".
Definition via FC18
If the constant cutting speed is defined via FC18, the setting of bit 6 in byte 2 in the "Signals
to concurring positioning axes" area determines how the speed value (bytes 8 ... 11) is
interpreted.
Setting via synchronized actions
For definition via synchronized actions, analog to the part program, the feedrate type defines
how the S value is interpreted.
Reading from part program and synchronized actions
The programmed cutting speed value can be determined in the part program and in the
synchronized actions by reading the following system variables:
● $P_CONSTCUT_S[<n>] (last programmed constant cutting speed)
● $AC_CONSTCUT_S[<n>] (actual constant cutting speed)
Defined range of values of the two new system variables: RV = {0, DBL_Max}
The programmed cutting speed value can also be read via the OPI interface.
Definition of the spindle speed type for the master spindle
Definition of the spindle speed type for the master spindle from part program, FC18 or
synchronized actions are written to the following setting data from all the usual sources:
SD43206 $SA_SPIND_SPEED_TYPE (spindle speed type for spindle start via PLC
interface)
The value range and the functionality correspond to the 15th G group (feedrate type).
Permissible values are G values: 93, 94, 95, 96, 961, 97 and 971.
Depending on the setting, for DB31, ... DBX30.1/2 (spindle start, clockwise/counter-clockwise)
either the speed from SD43200 $SA_SPIND_S or the cutting speed from
SD43202 $SA_SPIND_CONSTCUT_S is active:
93, 94, 95, 97 and 971:
96 and 961:
Definitions for spindle positioning
The definitions for spindle positioning using DB31, ... DBX30.4 (spindle positioning start) are
read from the following setting data:
SD43240 $SA_M19_SPOS (spindle position for spindle positioning with M19)
Basic Functions
Function Manual, 01/2015, 6FC5397-0BP40-5BA2
The master spindle is started with the speed from SD43200.
The speed of the master spindle is obtained from the specified
cutting velocity (SD43202) and the radius of the transverse
axis.
S1: Spindles
16.7 Programming
1281