Figure 12: Typical Sweeps In Constant Sweep Mode - Emerson PACSystems RX3i User Manual

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

Figure 12: Typical Sweeps in Constant Sweep Mode

Constant
Sweep
Abbreviations:
4.1.2.3 Constant Window Mode
In Constant Window mode, each sweep can consume a variable amount of time. The
Logic Window is executed in its entirety each sweep. The CPU alternates among the three
windows, allowing them to execute for a time equal to the value set for the Constant
Window timer. The overall CPU sweep time is equal to the time required to execute the
Housekeeping, Input Scan, Logic Window, and Output Scan phases of the sweep plus the
value of the Constant Window timer. This time may vary due to sweep-to-sweep
variances in the execution time of the Logic Window.
An application that requires a certain amount of time between the Output Scan and the
Input Scan, permitting inputs to settle after receiving output data from the program,
would be ideal for Constant Window mode.
The value of the Constant Window timer can be configured to be any value from 3 to 255
ms. The Constant Window timer value may also be set by the programming software or
by the user program using Service Request functions #3, #4, and #5.
The following figure illustrates three successive sweeps in Constant Window mode. Note
that the total sweep times may vary due to sweep-to-sweep variations in the Logic
Window, but the time given to the Communications and Background Windows is
constant. Some of the Communications or Background Windows may be skipped,
suspended, or run multiple times based on the Constant Window time.
CPU Operation
SWEEP n
t = 0 ms
HK
INPUT
LOGIC
OUTPUT
Time
CC
BPC
BG
SYS
HK = Housekeeping
PRG = Programmer Window.
BPC = Backplane Communications Window.
CC = Controller Communications Window
BG = Background Window
SWEEP n+1 SWEEP n+2
t = 100 ms t = 220 ms
HK HK
INPUT INPUT
LOGIC LOGIC
OUTPUT
CC
BPC
BG
SYS
BG
20 ms oversweep
OUTPUT
Section 4
October 2019
SWEEP n+3
t = 320 ms
HK
INPUT
LOGIC
OUTPUT
CC
BPC
BG
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