Siemens Sinumerik 840D sl Programming Manual page 138

Additional functions
4.8 Special functions
NOTICE
The premachining is changeover with the setting machine data $MN_SLASH_MASK==2
during a change of the skip level! All blocks located in the preprocessing memory are
traversed with the old skip level. The user normally does not have any control over the fill
level of the preprocessing memory. The user can see the following effect: A new skip level
is effective "some time" after the changeover!
Note
The part program command STOPRE vacates the preprocessing memory. If one switches
the skip level before STOPRE, then all the blocks after STOPRE are changed over securely.
The same is valid for an implicit STOPRE.
No drop in velocity is required while changing the DryRun mode with the setting machine
data 10704 $MN_DRYRUN_MASK==2. Here too, only the premachining that leads to the
above-mentioned restrictions, is switched. The following analogy is apparent from this:
Notice! This will also be active "sometime" after the changeover of the DryRun mode!
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Programming Manual, 06/09, 6FC5398-7BP10-1BA0
ISO Milling