Siemens SINUMERIK 840D sl Function Manual page 616

TE7: Continue machining - retrace support
15.2 Functional description
8. Retrace support:
Continue machining is initiated via PLC interface signal:
DB21, ... DBX0.2 = 1 (start retrace support)
For retrace support, RESU automatically selects the original machining program and
launches a block search with calculation as far as the program continuation point.
9. Continuation of part program machining:
Part program processing continues at the program continuation point in accordance with
the "Block search with calculation" standard function when two NC start commands occur
one after the other.
The first NC start command processes the action blocks. Retrace support ASUB
"CC_RESU_BS_ASUP.SPF" is initiated when the last action block is reached:
DB21, ... DBX32.6 = 1 (last action block active)
For more information about ASUB, see Chapter "RESU-specific part programs".
The second NC start command processes the approach block before part program
processing is resumed.
Note
Points 3 to 8 can be repeated as often as required.
Following retrace support, a new reverse travel is possible up to a maximum of the last
program continuation point.
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Function Manual, 09/2011, 6FC5397-2BP40-2BA0
Special Functions