Siemens SINUMERIK 840D sl Programming Manual page 383

Starting and end value of the curve table
The starting value for the beginning of the definition range of the curve table are the first
associated axis positions specified (the first traverse statement) within the curve table
definition. The end value of the definition range of the curve table is determined in
accordance with the last traverse command.
Within the definition of the curve table, you have use of the entire NC language.
All modal statements that are made within the curve table definition are invalid when the
table definition is completed. The parts program in which the table definition is made is
therefore before and after the table definition in the same state.
Note
The following are not permissible:
Preprocessing stop
Jumps in the leading axis movement (e.g., on changing transformations)
Traverse statement for the following axis only
Reversal of the leading axis, i.e., position of the leading axis must always be unique
CTABDEF and CTABEND statement on various program levels.
Job planning
Programming Manual, 03/2006 Edition, 6FC5398-2BP10-1BA0
Path traversing behavior
9.3 Curve tables (CTAB)
9-17