Siemens SINUMERIK 840D Function Manual page 782

S1: Spindles
18.4 Configurable gear adaptations
Figure 18-4
Note
In the case of M40, the spindle must be in open-loop control mode for automatic gear stage
selection with an S word. Otherwise the gear stage change is rejected and the following alarm
is set:
Alarm 22000 "gear stage change is not possible"
Note
An active reduction gear is not considered in the selection for the automatic gear stage change.
Permanently defining the gear stage with M41 to M45
The gear stage can be permanently defined in the part program with M41 to M45.
If a gear stage is specified via M41 to M45 that is not equal to the current (actual) gear stage,
then the following NC/PLC interface signals are set:
DB31, ... DBX82.3 (change over gear stage)
DB31, ... DBX82.0-82.2 (setpoint gear stage A to C)
782
Example for two gear stages with overlapping speed ranges for automatic gear stage
change (M40)
Axes and spindles
Function Manual, 06/2019, A5E47437747B AA