Rockwell Automation GMLC Reference Manual - Manual (Page 887)

Publication GMLC-5.2 - November 1999
850 CPU Utilization
These variable values are shown as a normalized percent (between 0 and
1). For example, the CPU Utilization value shown in the example, above,
indicates that nearly 25% of the CPU capacity is currently being used
(thus, 75% of CPU capacity is available), and peak CPU utilization has
been only about 26%.
Understanding CPU Utilization
To understand the effect of the CPU Utilization on program execution
and communication speed, you need to know how the motion controller
works. Internally, any motion controller lives by a clock, whose rate is
determined by the setting of the Servo Update Rate (parameter D47) in
the General page of the Configure Control Options dialog box, or with a
Control Settings block.
For example, if the Servo Update Rate is set to 1,000 Hz, the time
between ticks on the clock is 1 ms, as shown below.
At every tick of the clock, the motion controller stops whatever it is doing
and performs all the calculations necessary to keep the axes moving as
commanded by the application program. Thus, as more and more axes
and motion (moves, jogs, cams, etc.) are added to the application, less and
less time is available for external communications and program
execution.
Axes and
Motion
Tick Tick Tick
1 ms 1 ms
AxisLink
RIO
Program Tasks
Axes and
Motion
AxisLink
RIO
Program Tasks