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(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.
*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.
The following shows an example of the increase in execution time of a fixed scan execution type program.
With the settings above, the condition 1) will be 0.5ms < 5ms.
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.
Highest common factor of fixed scan execution interval
*1
< Interrupt disabled time ••• Condition 1)
• Fixed scan execution interval•••10ms, 5ms, 1ms, 0.5ms
• Highest common factor of fixed scan execution interval•••0.5ms
• Interrupt disabled time (DI)•••5ms (Interrupt enabled time (EI)•••less than 0.5ms)
Interrupt disabled time
Highest common factor of fixed
scan execution interval
Fixed scan execution interval set to
the corresponding program
Ex.
Ex.
Program execution
operation
Interrupt
enabled status
Disabled
Disabled Disabled
Enabled
Enabled
Interrupt disabled time = 5ms Interrupt disabled time = 5ms
nth scan(s) n + 1 th scans
EI EI
END END
DI
DI
Less than 0.5ms
Less than 0.5ms