Mitsubishi Electric Q01UCPU User Manual page 101

(3) Precautions
(a) Execution interval of a fixed scan execution type program
Execution interval of a fixed scan execution type program may increase from the preset interval depending on
the time set for disabling interrupts by the DI instruction (interrupt disabled time).
If the interrupt disabled time by the DI instruction becomes too long, use an interrupt program by fixed scan
interrupt (I28 to I31) instead of a fixed scan execution type program.
Highest common factor of fixed scan execution interval
*1 This is the highest common factor of execution interval set to multiple fixed scan execution type programs
When the condition 1) is satisfied, the actual execution interval of a fixed scan execution type program may
increase from the preset interval by the time shown in the expression below.
Interrupt disabled time
Highest common factor of
fixed scan execution interval
The following shows an example of the increase in execution time of a fixed scan execution type program.
• Fixed scan execution interval ••• 10ms, 5ms, 1ms, 0.5ms
Ex.
• Highest common factor of fixed scan execution interval ••• 0.5ms
• Interrupt disabled time (DI) ••• 5ms
(Interrupt enabled time (EI) ••• less than 0.5ms)
With the settings above, the condition 1) will be 0.5ms < 5ms.
Program execution
operation
Interrupt enabled/
disabled status
The execution time of a fixed scan execution type program whose execution interval is set to 10ms increases
100ms (5  0.5 × 10 = 100) at the most.
Fixed scan execution interval set to
the corresponding program
n scan
EI
DI
END
Disabled
Enabled
Less than 0.5ms
Interrupt disabled time = 5ms
CHAPTER 2 APPLICATION OF PROGRAMMING
*1
< Interrupt disabled time ••• Condition 1)
n+1 scan
EI
DI
Disabled
Enabled
Less than 0.5ms
Interrupt disabled time = 5ms
2
END
Disabled
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