Siemens SINUMERIK 840D Function Manual page 308

R1: Referencing
10.5 Referencing with incremental measurement systems
Figure 10-10 Reference point position
When the reference point is reached, the machine axis is stopped and the actual-value system
is synchronized with the reference point value n specified by the NC/PLC interface.
MD34100 $MA_ REFP_SET_POS[<n>] (reference point value)
The selection of the reference point value is performed via the NC/PLC interface:
DB31, ... DBX2.4 ... 7 (reference point value 1 ... 4)
The actual-value system is synchronized to the reference point value that was selected at the
time the reference cam was reached in Phase 1 (DB31, ... DBX12.7 == 1).
The machine axis is now referenced. The interface signal is set as feedback to the PLC user
program, depending on the active measuring system:
DB31, ... DBX60.4/5 (referenced/synchronized 1/2) = 1
Features of Phase 3
● Feedrate override is active.
● Feed stop (channel-specific and axis-specific) is active.
● NC stop and NC start are active.
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Axes and spindles
Function Manual, 06/2019, A5E47437747B AA