Siemens SINUMERIK 840D sl Function Manual page 56

A4: Digital and analog NCK I/Os
1.2 NCK I/O via PLC
Threshold values
The threshold values used for comparisons on comparator byte 1 or 2 must be stored as
setting data. For every comparator input bit [b], you must enter a separate threshold value:
SD41600 $SN_COMPAR_THRESHOLD_1[b]
(threshold values for input bit [b] of comparator byte 1); b = 0 to 7
Comparator signals as digital NCK inputs
All NC functions that are processed as a function of digital NCK inputs can also be controlled
by the signal states of the comparators. The byte address for comparator byte 1 (HW byte
128) or 2 (HW byte 129) must be entered in the MD associated with the NC function
("Assignment of hardware byte used").
Example
"Multiple feedrates in one block" NC function
Entry in channel-specific machine data:
MD21220 $MC_MULTFEED_ASSIGN_FASTIN = 129
This activates various feedrate values as a function of the status of comparator byte 2.
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Function Manual, 09/2009, 6FC5397-1BP20-0BA0
Extended Functions