Siemens SINUMERIK 840D sl Function Manual page 695

Dimension system metric/inch
MD10260 CONVERT_SCALING_SYSTEM=1
With the above machine data setting, the cam positions no longer refer to the basic system,
but to the system configured in machine data: :
MD10270 POS_TAB_SCALING_SYSTEM
MD10270 POS_TAB_SCALING_SYSTEM=0:
MD10270 POS_TAB_SCALING_SYSTEM=1:
MD10270 POS_TAB_SCALING_SYSTEM
The above machine data therefore defines the dimension system for position parameters
from setting data:
SD41500 to SD41507
A switchover with G70/G71 or G700/G710 has no effect.
Sensing of cam positions
To set the cam signals, the actual position of the axes is compared to the cam position.
Writing/reading of cam positions
The setting data can be read and written via HMI, PLC and part program.
Accesses from the part program are not synchronous to machining.
Synchronization can only be achieved by means of a programmed block preprocessing stop
(STOPRE command).
It is possible to read and write the cam positions with FB2 and FB3 in the PLC user program.
Axis/cam assignment
A cam pair is assigned to a machine axis using general machine data:
MD10450 SW_CAM_ASSIGN_TAB[n]
(assign software cams to machine axes).
Note
Changes to an axis assignment take effect after the next NCK power-up.
Cam pairs to which no axis is assigned are not active.
A cam pair can only be assigned to one machine axis at a time.
Several cam pairs can be defined for one machine axis.
Extended Functions
Function Manual, 01/2008, 6FC5397-1BP10-3BA0
Software cams, position switching signals (N3)
9.2 Cam signals and cam positions
Metric
Inch
695