Emerson PNC001-A Series User Manual

PACSystems™ RX3i and RSTi-EP CPU Reference Manual Section 4
GFK-2222AK October 2019
CPU Operation 85
Figure 12: Typical Sweeps in Constant Sweep Mode
Abbreviations:
HK = Housekeeping
PRG = Programmer Window.
BPC = Backplane Communications Window.
CC = Controller Communications Window
OUTPUT
CC
SYS
BG
BG
BPC
HK
INPUT
LOGIC
SWEEP n+2
t = 220 ms
HK
INPUT
BG
HK
INPUT
LOGIC
LOGIC
HK
INPUT
LOGIC
OUTPUT
CC
BPC
BG
SYS
OUTPUT
20 ms oversweep
Constant
Sweep
Time
BPC
CC
OUTPUT
SWEEP n+1
t = 100 ms
SWEEP n
t = 0 ms
SWEEP n+3
t = 320 ms
BG = Background Window
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.

Emerson PNC001-A Series Specifications

General

Brand	Emerson
Model	PNC001-A Series
Category	Controller
Language	English