Mitsubishi 00JCPU User Manual page 84

(4) 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.
Example
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
2 - 39
Highest common factor of fixed scan execution interval
Interrupt disabled time
Interrupt disabled time
Highest common factor of scan
execution interval
Fixed scan execution interval
•
Highest common factor of fixed scan execution interval
•
Interrupt disabled time (DI)
•
0.5ms)
n scan
DI
Disabled
Less than 0.5ms
Interrupt disabled time = 5ms
Figure 2.41 Program execution and interrupt enabled/disabled status
0.5 10 = 100) at the most.
Condition 1)
Fixed scan execution interval set to
×
the corresponding program
10ms, 5ms, 1ms, 0.5ms
5ms (Interrupt enabled time (EI)
EI
DI
END
Disabled
Enabled
Interrupt disabled time = 5ms
*1
<
0.5ms
less than
n+1 scan
EI
END
Enabled Disabled
Less than 0.5ms