Figure 42: Typical Sweeps In Constant Sweep Mode - GE PACSystems RX7i Reference Manual

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
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.
Constant
Sweep
Time
Abbreviations:
HK = Housekeeping
PRG = Programmer Window.
BPC = Backplane Communications Window.
CC = Controller Communications Window
BG = Background Window
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For EGD configured on Embedded Ethernet interface of CPE302/CPE305/CPE310, refer to A.3.6 for Constant sweep impact.
GFK-2222AD
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page, configured for either consumption or production, can add up to 1 ms to
SWEEP n SWEEP n+1
t = 0 ms t = 100 ms
HK
INPUT INPUT
LOGIC LOGIC
OUTPUT
CC
BPC
BG
SYS
OUTPUT

Figure 42: Typical Sweeps in Constant Sweep Mode

April 2018
SWEEP n+2
t = 220 ms
HK HK
INPUT
LOGIC
OUTPUT
CC
BPC
BG
SYS
BG
20 ms oversweep
Chapter 4. CPU Operation
SWEEP n+3
t = 320 ms
HK
INPUT
LOGIC
OUTPUT
CC
BPC
BG
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