Siemens SINUMERIK 840D sl Function Manual page 1241

The gear stage is not changed if:
● The spindle is positioned via synchronized actions.
● The spindle is traversed in the axis mode.
Note
For further details, please refer to the section "Specification of a gear stage in part program".
Exception:
The block change is not affected by the specification of a gear stage in synchronized actions.
Manual specification of a gear stage
Outside a part program that is running, the gear stage can also be changed without a request
from the NC or the machine. This is the case, for example, when a gear stage is changed
manually.
To select the appropriate parameter set, the NC must be informed of the current gear stage.
To enable this, the control or the part program must be in the reset state.
Supplementary conditions
Transfer of the gear stage to the NC is initiated when
NC/PLC IS:
DB31, ... DBX16.0-16.2 (actual gear stage A to C) changes.
These three bits must be set continuously during operation.
Successful transfer is acknowledged with NC/PLC IS:
DB31, ... DBX82.0-82.2 (set gear stage A to C)
to the PLC.
NC/PLC IS:
DB31, ... DBX16.3 (gear changed)
must not be set.
If position control is active when a new gear stage is specified by the PLC with
DB31, ... DBX16.0-16.2, then it is switched off for the duration of this changeover sequence.
Basic Functions
Function Manual, 01/2015, 6FC5397-0BP40-5BA2
S1: Spindles
16.4 Configurable gear adaptation
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