
B–61863E–1/06
2. TASK CONTROL FUNCTION
PMC CONTROL SOFTWARE
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(3) Execution ratio of PMC screen display to C program tasks
As explained in (1), PMC screen display (*c) has priority over the
execution of C program tasks (*d). So, when PMC screen display is
being performed, C program tasks do not generally have ample
opportunities to run.
When LANGUAGE EXEC RATIO is set on the system parameter
screen of the PMC programmer function, PMC screen display (*c)
and C program tasks (*d) can be performed according to the set ratio
as shown in the figure below.
By setting LANGUAGE EXEC RATIO, the C program can be
executed at regular intervals even when PMC screen display is in
progress.
When PMC screen display is not performed, C program tasks are
performed regardless of the LANGUAGE EXEC RATIO setting.
[Setting range of LANGUAGE EXEC RATIO]
0% to 99%
[Example]
When there is a highest-priority C task, the execution period is 8 ms,
LADDER EXEC is set to 80%, and LANGUAGE EXEC RATIO is
set to 50%, the following timing chart results:
0 8 16 24 (ms)
*a
*b
*c
*d
CAUTION
1 As the LANGUAGE EXEC RATIO value increases, the processing
time for PMC screen display decreases, which delays display
operation. Normally, set LADDER EXEC RATIO to 50%.
2 The priority of first-level and second-level ladder programs, the
highest-priority C program, and PMC screen display is controlled
by the PMC control software. The priority cannot be changed by
user applications.
3 For third-level ladder programs, set the task priority in the link
control statement data in the same way as for C program tasks.
If the priority is set to 0, (that is, if the link control statement
creation tool does not use third-level ladder programs,)
third-level ladder programs are not executed.