Rockwell Automation GMLC Reference Manual - Manual (Page 888)

Publication GMLC-5.2 - November 1999
Understanding CPU Utilization 851
Normally this is not a problem, but as CPU utilization exceeds 80 – 90%
of capacity, program execution can grind to a virtual halt and external
communications can fail. Until this point is reached, however, adding
axes and motion has very little effect upon program execution and
external communications, as shown in the following graph.
This graph was generated by timing a small application program running
in the motion controller (using the Free Running Timer) as various
additional axes and motion were added. As you can see, there is virtually
no effect on program execution speed until a certain threshold is
reached—and then the effect is dramatic!
The threshold where program execution grinds to a halt depends mostly
on whether you are using RIO and/or AxisLink. Approximate program
execution thresholds are given in the table below.
CPU Utilization Program Execution Thresholds
Using RIO Using AxisLink CPU Utilization Threshold
No No 90%
No Yes 80%
Yes No 90%
Yes Yes 70%
CPU Utilization
Program Execution Time (S)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0.4 0.5 0.6 0.7 0.8 0.9 1