Siemens SINUMERIK 840D sl Function Manual page 1654

Detailed Description
2.3 Configurable gear adaptation
Following acknowledgment of gear step change via the PLC
with NC/PLC IS:
DB31, ... DBX16.3 (Gear changed)
the spindle is in speed control mode (DB31, ... DBX84.7).
For further instructions on signal exchange between PLC and NC, see:
Literature:
/FB1/ Function Manual Basic Functions; Diverse interface signals (A2)
Specify gear step in the part program
In the case of M40, the spindle must be in open-loop control mode for automatic gear step
selection with an S value. The gear step change is otherwise rejected and alarm 22000
"Gear change not possible" is output.
Automatic selection with active M40
The gear step is automatically selected by the control. The control checks which gear step is
possible for the programmed spindle speed (S value).
If a gear step is found, which is not equal to the current (actual) gear step, the following
NC/PLC interface signals are then set:
DB31, ... DBX82.3 (change over gear stage)
DB 31, ... DBX82.0-82.2 (Set gear stage A to C)
While the appropriate gear step is being determined, a gear step change is only requested if
the new speed is not within the permissible speed range of the active gear step.
If necessary, the speed is limited to the max. speed of the current gear step or increased to
the minimum speed of the current gear step, and the following NC/PLC interface signal is
set.
DB 31, ... DBX83.1 (Setpoint speed restricted)
44
Basic logic functions: Spindles (S1)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0