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M
ain
Chapter 1 Configuration and Operation Mode of Programs
1-6
WORD Flag Name Name Description
%FW50 _SCAN_MAX
Maximum scan
time
The longest scan time (update in case of occurrence only), in
0.1ms
%FW51 _SCAN_MIX Minimum scan time
The shortest scan time (update in case of occurrence only), in
0.1ms
%FW52 _SCAN_MAX Current scan time Running time of this scan (scan update), in 0.1ms
1.1.4 Program Composition
T
he program is composed of all function factors required to perform a specific control and they are saved in the
basic unit’s RAM or flash memory. The function factors to execute the program can be generally divided as below.
Function factors Executing details
Initialization program
•
After applying power, it is the program that is firstly executed after completing the self-
initialization operations required to operate the PLC. It should run until the INIT_DONE
command executes.
•
When the initialization program runs, only the initialization program is available until the
INIT_DONE command runs; the scan program and fixed cycle, external interrupt, internal
device task program are not executed. All other embedded functions such as I/O refresh, high
speed counter, communication are normally executed.
•
It is used to program various operations required for the initial settings of the system
configured with the high performance XGB PLC.
Scan program
•
Repeated regularly at every scan. It performs the operation repetitively from the first step to
the last step in order of being written.
•
If the fixed cycle interrupt, external contact interrupt, high speed counter interrupt occur
during execution of the scan program, it will stop the scan program and return to the
scan program after executing the relevant interrupt program.
Fixed cycle interrupt
program
•
Executed at every set cycle regardless of the scan program. It can be applied to execute the
following time conditions.

Execution at the shorter time interval than 1 scan processing time

Execution at the longer time interval than 1 scan processing time

Execution at the fixed time interval
External contact
interrupt program
•
Executed every time the input conditions (rising edge, falling edge, transition) of the set
external input signal occur. It can be applied when immediate execution is required for external
input conditions.
High speed counter
interrupt program
•
Executed when the high speed counter’s current value is matched with the set value.
Internal device
interrupt program
•
Executed when the set internal device is matched with relational conditions.
•
Detects whether starting conditions of the internal device interrupt occurs during END after
executing the scan program
Subroutine program
•
Executed only when the input condition of the CALL command is On.
Notice
1) Make the interrupt program as shortly as possible. In case the same interrupt occurs repeatedly during
executing the interrupt program, O/S watchdog error may occur with non-execution of the scan program.
(In case the self-interrupt occurs during executing the interrupt program, task conflict error may occur.)
2) Although interrupts with low priority occur several times during executing the one with high priority, the interrupt
will run just once so you should pay attention to set up the priority.