B3: Distributed systems - 840D sl only
2.2 NCU link
Extended Functions
84 Function Manual, 03/2013, 6FC5397-1BP40-3BA1
Position control cycle clock
The position control cycle clock is set as a ratio to the basic system cycle clock. For the
SINUMERIK 840D sl, the ratio is fixed (1:1) and cannot be changed. The current position
control cycle clock is displayed in the machine data:
MD10061 $MN_POSCTRL_CYCLE_TIME
Note
Permitted position control cycle clocks
For the NCU link, depending on the number of NCUs in the link group, only the following
position control cycle clocks [ms] are set:
• 2 NCU: 2.0, 2.5, 3.0, 3.5, 4.0
• 3 NCU: 3.0, 3.5, 4.0
See Section "Configuration (Page 85)".
Interpolator cycle clock
The interpolator cycle clock is set as a ratio of the basic system cycle clock. The setting is
made via the following machine data:
MD10070 $MN_IPO_SYSCLOCK_TIME_RATIO
The actual interpolator cycle clock is displayed in machine data:
MD10071 $MN_IPO_CYCLE_TIME
Notes on setting
Cycle clock settings
It is recommended the following settings are made:
● The default 90% setting for the CPU time share of the NCK should be retained:
MD10185 $MN_NCK_PCOS_TIME_RATIO
● The system cycle clocks must be set so that the average system utilization caused by the
interpolator and the position controller does not exceed 60% in normal program
operation. As maximum value, 90% should be not be exceeded.
Note:
In special circumstances, maximum values > 100% can be displayed.
Lowest cyclic communication load
The lowest cyclic communication load during the link communication results for a cycle clock
ratio of interpolator cycle clock to position control cycle clock of 1:1. With activated "Dynamic
Servo Control (DSC)" drive function, this is generally the most effective setting.
Disadvantage: No telegram repetitions are possible for the link communication.
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