Allen-Bradley 1756-L63XT, User Manual

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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