Scan Parameters - Emerson PACSystems RX3i User Manual

PACSystems™ RX3i and RSTi-EP CPU Reference Manual
GFK-2222AK
3.2.5

Scan Parameters

These parameters determine the characteristics of CPU sweep execution.
Scan Parameters
Sweep Mode The sweep mode determines the priority of tasks the CPU performs during the sweep
and defines how much time is allotted to each task. The parameters that can be
modified vary depending on the selection for sweep mode.
The Controller Communications Window, Backplane Communications Window, and
Background Window phases of the PLC sweep can be run in various modes, based on
the PLC sweep mode.
Choices:
▪
▪
▪
Logic Checksum The number of user logic words to use as input to the checksum algorithm each
Words sweep.
Valid range: 0 through 32760, in increments of 8.
Default: 16.
CPU Configuration
Normal mode: The PLC sweep executes as quickly as possible. The overall PLC
sweep time depends on the logic program and the requests being processed in the
windows and is equal to the time required to execute the logic in the program plus
the respective window timer values. The window terminates when it has no more
tasks to complete. This is the default value.
Constant Window mode: Each window operates in a Run-to-Completion mode.
The PLC alternates among three windows for a time equal to the value set for the
window timer parameter. The overall PLC sweep time is equal to the time required
to execute the logic program plus the value of the window timer. This time may
vary due to sweep-to-sweep differences in the execution of the program logic.
Constant Sweep mode: The overall PLC sweep time is fixed. Some or all of the
windows at the end of the sweep might not be executed. The windows terminate
when the overall PLC sweep time has reached the value specified for the Sweep
Timer parameter.
Section 3
October 2019
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