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Rockwell Automation Publication 1756-UM001O-EN-P - October 2014 165

Develop Applications Chapter 10

System Overhead Time Slice

The controller communicates with other devices at a specified rate (scheduled) or

when processing time is available to service the communication.

The system overhead time slice specifies the percentage of time a controller

devotes to service communication. If you have a continuous task, the system

overhead time slice that is entered on the Advanced tab of the Controller

Properties dialog box specifies the continuous task/service communication ratio.

However, if there is no continuous task, the overhead time slice has no effect.

Table 39

shows the ratio between the continuous task and service

communication at various system overhead time slices for RSLogix 5000, version

16.03.00 or later, and Logix Designer version 21.00.00 or later.

As shown in the table, if the system overhead time slice is less than or equal to

50%, the duration stays fixed at 1 ms. The same applies for 66% and higher,

except there are multiple 1 ms intervals. For example, at 66% there are two 1 ms

intervals of consecutive time and at 90% there are nine 1 ms intervals of

consecutive time.

Table 39 - Ratio between Continuous Task and Service Communication

Time Slice Continuous Task Duration Service Communication Duration

10% 9 ms 1 ms

20% 4 ms 1 ms

25% 3 ms 1 ms

33% 2 ms 1 ms

50% 1 ms 1 ms

66% 1 ms 2 ms

75% 1 ms 3 ms

80% 1 ms 4 ms

90% 1 ms 9 ms

1 2 ... 160 161 162 163 164 165 166 167 168 169 170 ... 211 212

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Allen-Bradley ControlLogix Manual de usuario Pagina 165