Siemens SINUMERIK 840D sl Programming Manual page 163

For certain kinematic transformations (e.g. TRANSMIT), the position of the machine axes
cannot be determined uniquely from the positions in the workpiece coordinate system (WCS)
(non-uniqueness). In the normal traversing operation, the uniqueness normally results from
the previous history and the condition that a continuous movement in the WCS must
correspond to a continuous movement in the machine axes. When monitoring the software
limits using the CALCPOSI function, the current machine position is therefore used to
resolve non-unique determinability in such cases. If necessary, a STOPRE must be
programmed in front of CALCPOSI to input valid machine axis positions to the function.
It is not guaranteed that the separation to the protection zones specified in _DLIMIT[3] can
always be maintained for a movement on the specified traversal path. Therefore if the end
point returned in _MOVDIST is lengthened by this distance, no protection zone is violated,
even though the straight line may pass extremely close to a protection zone.
Note
You will find details on working area limitations in the
/PG/ Fundamentals Programming Guide,
on the software limits in
/FB1/ Function Manual, Basic Functions; Axis Monitoring, Protection Zones (A3).
Job planning
Programming Manual, 03/2006 Edition, 6FC5398-2BP10-1BA0
4.3 Checking for protection zone violation, working area limitation and software limits
Protection zones
4-13