2 - 39
(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.
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)
Figure 2.41 Program execution and interrupt enabled/disabled status
Interrupt disabled time
Highest common factor of scan
execution interval
Fixed scan execution interval set to
the corresponding program
×
Program execution
operation
Interrupt enabled/
disabled status
Disabled Disabled Disabled
Enabled
Enabled
Interrupt disabled time = 5ms Interrupt disabled time = 5ms
n scan
n+1 scan
EI
EI
END END
DI
DI
Less than 0.5ms Less than 0.5ms
To Next Page
Loading...
Need help?
General
