Siemens SINUMERIK 840D sl Function Manual page 972

Indexing Axes (T1)
Traversing of indexing axes
16.2.4 Traversing of indexing axes by PLC
Indexing axes can also be traversed from the PLC user program.
There are various methods:
● Concurrent positioning axes
● Asynchronous subroutines (ASUBs)
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The indexing position to be approached can be specified by the PLC.
References:
/FB2/ Function Manual, Extended Functions; Positioning Axes (P2)
References:
/FB1/ Function Manual, Basic Functions; Mode Group, Channel, Program Operation,
Reset Response (K1)
Function Manual, 03/2009, 6FC5397-1BP10-4BA0
Extended Functions