Rockwell-automation 1794-L34 FlexLogix Controller System User Manual Manuel d'utilisateur télécharger pdf (Page 83)

Publication 1794-UM001G-EN-P - January 2007

Develop Applications 83

the system overhead percentage does increase communications

performance, it also increases the amount of time it takes to execute a

continuous task - increasing overall scan time

The table below shows the ratio between the continuous task and the

system overhead functions:

At a time slice of 10%, system overhead interrupts the continuous task

every 9 ms (of continuous task time), as illustrated below.

The interruption of a periodic task increases the elapsed time (clock

time) between the execution of system overhead, as shown below.

At this time slice: The continuous tasks

runs for:

And then overhead occurs

for up to:

10% 9 ms 1 ms

20% 4 ms 1 ms

33% 2 ms 1 ms

50% 1 ms 1 ms

Legend:

Task executes.

Task is interrupted (suspended).

periodic

1 ms 1 ms

system overhead

9 ms 9 ms

continuous task

0 5 10 15 20 25

elapsed time (ms)

1 ms 1 ms 1 ms 1 ms 1ms

periodic task

1 ms 1 ms

system overhead

9 ms of continuous task time 9 ms of continuous task time

continuous task

0 5 10 15 20 25

elapsed time (ms)

1 2 ... 78 79 80 81 82 83 84 85 86 87 88 ... 129 130

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Rockwell-automation 1794-L34 FlexLogix Controller System User Manual Manuel d'utilisateur Page 83