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GFK-0467K Chapter 2 System Operation 2-3
2
All of these steps execute every sweep. Although the Programmer Communications Window
opens each sweep, programmer services only occur if a board fault has been detected or if the
programming device issues a service request; that is, the Programmer Communications Window
first checks for work to do and exits if there is none. The sequence of the standard program sweep
is shown in the following figure.
Figure 2-1. PLC Sweep
SYSTEM
COMMUNICATIONS
I/O
?
ENABLED
RUN
?
MODE
a43064
START-OF-SWEEP
START NEXT SWEEP
INPUT SCAN
USER PROGRAM
PROGRAMMER
OUTPUT SCAN
I/O
NO
LOGIC SOLUTION
NO
NO
YES
YES
YES
HOUSEKEEPING
DATA
PROGRAM
DATA
PROGRAMMER
DIAGNOSTICS
SCAN
PLC
OF
TIME
SYSTEM
HOUSEKEEPING
?
ENABLED
EXECUTION
INPUT
OUTPUT
COMMUNICATIONS
SERVICE
COMMUNICATIONS
CALCULATION
CHECKSUM