Siemens SINUMERIK 840Di Function Manual page 1108

Detailed description
2.12 Block descriptions
Alternatively, the PLC user program can also request the check for the PLC prior to calling
FC "POS_AX".
By calling this function several times in succession, a better response reaction by the axes
can be obtained as the changeover process in the FC can be omitted.
Activation through the PLC user program is executed in the corresponding axis interface in
byte 8.
After return of the check, the axis can again be programmed by the NC program.
Note
Rotary axes can be positioned by the shortest possible route through the programming of a
negative feed value in absolute programming mode. In incremental mode (parameter "IC" :=
TRUE), the traversing direction can be defined by means of the parameter "Pos" sign:
Positive sign indicates travel in a positive direction
Negative sign indicates travel in a negative direction
After the FC has been called, ACCU1 contains an error statement by the NCK (but not if the
output parameters are assigned to a data block). This is generally the value 0 (signifies: No
error has occurred). The interpretation of other numerical values is shown in the following
table.
FC 15 must be called cyclically until the "Active" signal produces an edge transition from 1 to
0. Only when the "Active" signal has a 0 state can the axis concerned be restarted (the next
start must be delayed by at least one PLC cycle). This also applies when the assignment in
data byte 8 has changed.
The function cannot be aborted by means of parameter "Start", but only by means of the
axial interface signals (e.g., delete distancetogo). The axial interface also returns status
signals of the axis that may need to be evaluated (e.g., exact stop, traverse command).
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.
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Power Line Basic PLC Program (P3)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0