Siemens sinumerik 840D sl Function Manual page 105

Mode change
Tool length compensation remains active even if the mode is changed and can be executed
in any mode.
If a tool length compensation is interpolated on account of $AA_TOFF[ ] during mode
change, the mode change cannot take place until the interpolation of the tool length
compensation has been completed. Alarm 16907 "Channel %1 action %2 ALNX possible
only in stop state" is issued.
Behavior with REF and block search
Tool length offset is not considered during reference point approach REF in JOG mode.
The instructions TOFFON( ) and TOFFOF( ) are not collected and output in an action block
during block search.
System variables
In the case of online tool length offset, the following system variables are available to the
user:
System variables
$AA_TOFF[ ]
$AA_TOFF_VAL[ ]
$AA_TOFF_LIMIT[ ]
$AA_TOFF_PREP_DIFF[ ]
References: /PGA1/ LHB System Variables
Boundary conditions
The online tool length offset function is an option and is available during "generic 5-axis
transformation" by default and for "orientable tool holders".
If the tool is not perpendicular to the workpiece surface during machining or the contour
contains curvatures whose radius is smaller than the compensation dimension, deviations
compared to the actual offset surface are produced. It is not possible to produce exact offset
surfaces with one tool length compensation alone.
Special functions: 3-Axis to 5-Axis Transformation (F2)
Function Manual, 11/2006, 6FC5397-2BP10-2BA0
Meaning for online tool length offset
Position offset in the tool coordinate system
Integrated position offset in the WCS
Query whether the tool length offset value is close to the limit
Magnitude of the difference between the currently active value of
$AA_TOFF[ ] and the value prepared as the current motion block.
Detailed description
2.11 Online tool length offset
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