Siemens SINUMERIK 840Di Function Manual page 1121

On completion ("InPos" is True, "Start" changes to zero), the axis/spindle check function is
switched to a neutral status by FC "SpinCtrl".
Alternatively, the PLC user program can also request the check for the PLC prior to calling
FC "SpinCtrl".
By calling this function several times in succession, a better response reaction by the
spindle/axis can be obtained as the changeover process in the FC can be omitted.
Activation through the PLC user program is executed in the corresponding spindle interface
in byte 8.
After return of the check, the spindle can again be programmed by the NC program.
Note
Please note:
FC 18 must be called cyclically until signal "InPos" or, in the case of an error "Error",
produces an edge transition of 1 to 0. Only when the "InPos"/"Error" signal has a 0 state can
the axis/spindle concerned be "started" or "stopped" again (the next "start" must be delayed
by at least one PLC cycle). This also applies when the assignment in data byte 8 on the axial
interface has been changed.
Abort:
The function cannot be aborted by means of parameter "Start" or "Stop", but only by means
of the axial interface signals (e.g., delete distancetogo). The axial interface also returns axis
status signals that may need to be evaluated
(e.g., exact stop, traverse command).
InPos on spindle - rotation/oscillation:
For the "Rotate spindle" and "Oscillate spindle" functions, the meaning of the "InPos"
parameter is defined as follows:
Setpoint speed is output --> function was started without error.
The reaching of the required spindle speed must be evaluated using the spindle interface.
Simultaneity:
Several axes can be traversed simultaneously or subject to a delay by the blocks FC 15, 16
and 18. The upper limit is defined by the maximum number of axes. The NCK handles the
PLC function request (FC 15, 16, 18) via independent interfaces for each axis/spindle.
Axis disable:
With the axis disabled, an axis controlled via FC 18 will not move. Only a simulated actual
value is generated. (Behavior as with NC programming).
Warning
If several block calls (FC 15, FC 16, FC 18) are programmed for the same axis/spindle in the
PLC user program, then the functions concerned must be interlocked by conditional calls in
the user program. The conditional call of a started block (parameter Start or Stop = TRUE)
must be called cyclically until the signal state of output parameter Active or InPos changes
from 1 to 0.
Power Line Basic PLC Program (P3)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
Detailed description
2.12 Block descriptions
2-209