Siemens SINUMERIK 840D sl Function Manual page 796

Positioning Axes (P2)
Motion behavior and interpolation functions
Marginal conditions
Axes/spindles currently operating according to the NC program are not controlled by the PLC.
Command axis movements cannot be started via non-modal or modal synchronized actions
for PLC-controlled axes/spindles. Alarm 20143 is signaled.
Sequence coordinator
The sequence of autonomous single-axis functions with the respective transfers is
represented in a so-called "Use Case" overview:
NCK controls: PLC wants to accept control of the axis/spindle
Use Case 1: Cancel operation of axis/spindle
Use Case 2: Stop axis/spindle
Use Case 3: Resume axis/spindle motion
Use Case 4: Reset axis/spindle
PLC controls: PLC wants to relinquish control of the axis/spindle
Axis control by PLC
Accept control of axis/spindle
The channel behavior triggered by the NC program run is decoupled. Control of the
axis/spindle is transferred via the axial VDI interface with the MC/PLC interface signal:
DB31, ... DBX28.7 (PLC controls axis)
Description of operational sequence:
1. PLC to NCK with NST:
2. NCK checks: Is the axis a main run axis or a neutral axis
3. NCK checks whether other axes can be controlled by the PLC.
4. NCK confirms acceptance and transfers the axis status with NST:
5. PLC has accepted control of the axis/spindle.
796
DB31, ... DBX28.7 (PLC controls axis) == 1
-> Accept control of an axis
DB31, ... DBX63.1 ("PLC controls axis") == 1 to the PLC
System variable $AA_SNGLAX_STAT as scannable current axis status.
Function Manual, 03/2009, 6FC5397-1BP10-4BA0
Extended Functions