Mitsubishi Electric L02SCPU User's Manual And Reference page 72

(1) Processing
(a) When two or more fixed scan execution type programs exist
Each fixed scan execution type program is executed at specified time intervals. If two or more fixed scan
execution type programs reach the specified time at the same timing, programs will be executed in ascending
order of the numbers set in the Program tab of the PLC Parameter dialog box.
(b) When both fixed scan execution type program and interrupt program exist
When a fixed scan execution type program and an interrupt program (I28 to I31) reach the specified time at the
same timing, the interrupt program will be given priority.
(c) When the execution condition is established during END processing
When the execution condition is established during the waiting time of the constant scan execution or the END
instruction, a fixed scan execution type program is executed.
Constant scan
Fixed scan interval
END processing
Scan execution
type program
Fixed scan execution
type program
(2) Processing at program execution type change
For how to save and restore data in the index register when the program execution type is changed, refer to 
Page 60, Section 2.7 (4). The method is the same as that for interrupt programs.
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2
*
1
*
Condition
established
*1: Waiting time
*2: If processing is not completed within
the waiting time, the scan time increases.