Emerson PACSystems RX3i User Manual page 92

PACSystems™ RX3i and RSTi-EP CPU Reference Manual
GFK-2222AK
4.1.2.2 Constant Sweep Mode
In Constant Sweep mode, each sweep begins at a specified Constant Sweep time after the
previous sweep began. The Logic Window is executed in its entirety each sweep. If there
is sufficient time at the end of the sweep, the CPU alternates among the Controller
Communications, Backplane Communications, and Background Windows, allowing them
to execute until it is time for the next sweep to begin. Some or all of the Communications
and Background Windows may not be executed. The Communications and Background
Windows terminate when the overall CPU sweep time has reached the value specified as
the Constant Sweep time.
One reason for using Constant Sweep mode is to ensure that I/O data are updated at
constant intervals.
The value of the Constant Sweep timer can be configured to be any value from 5 to 2550
ms. The Constant Sweep timer value may also be set and Constant Sweep mode may be
enabled or disabled by the programming software or by the user program using Service
Request function #1. The Constant Sweep timer has no default value; a timer value must
be set prior to or at the same time Constant Sweep mode is enabled.
The Ethernet Global Data
add up to 1 ms to the sweep time. This sweep impact should be considered when
configuring the CPU constant sweep mode and setting the CPU watchdog timeout.
If the sweep exceeds the Constant Sweep time in a given sweep, the CPU places an
oversweep alarm in the CPU fault table and sets the OV_SWP (%SA0002) status reference
at the beginning of the next sweep. Additional sweep time due to an oversweep condition
in a given sweep does not affect the time given to the next sweep.
The following figure illustrates four successive sweeps in Constant Sweep mode with a
Constant Sweep time of 100 ms. Note that the total sweep time is constant, but an
oversweep may occur due to the Logic Window taking longer than normal.
60 For EGD configured on Embedded Ethernet interface of CPE302/CPE305/CPE310, refer to A.3.6 for Constant sweep impact.
CPU Operation
page, configured for either consumption or production, can
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Section 4
October 2019
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