Siemens SINUMERIK 840D sl Function Manual page 539

Constraints
Collected S values
The meaning of an S value in the parts program depends on the feed type that is currently
active:
G93, G94, G95, G97, G971
G96, G961
If the feed operation is changed (e.g. for a tool change) before output of the system variable
$P_SEARCH_S, the original setting from the target block in the parts program must be
restored to avoid use of the wrong type of feed.
Collected direction of rotation
For output of the direction of rotation, the system variable $P_SEARCH_SDIR is assigned
default value "-5" at the start of the block search. This value has no effect on output.
This ensures that the last spindle operating mode is retained for a block search across
program section in which spindles are not programmed with a direction of rotation,
positioning or axis mode.
The programming of M19, SPOS and SPOSA is collected as "M-19" (internal M19) in the
system variables $P_SEARCH_SDIR alternatively to M3, M4, M5 and M70.
For the output of "M-19", the positioning data are read internally from the system variables
$P_SEARCH_SPOS and $P_SEACH_SPOSMODE. Both system variables can also be
written, for example, to make corrections.
Note
Because of the assignments described above (e.g. M[n] = $P_SEARCH_SDIR[n]), the
values "–5" and "–19" generally remain hidden from the user and only have to be observed in
the case of special evaluation of the system variables in the ASUB.
Basic logic functions: Auxiliary Function Output to PLC (H2)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
The S value is interpreted as the speed
The S value is interpreted as a constant cutting rate
Detailed description
2.12 Block search
51