
1
2
3
4
5
6
Cautionary Items 6-9
6
Cautionary Items
A freeze may occur if subtasks are continuously started (START command) and ended (EXIT TASK
command) by a main task in an alternating manner.
This occurs for the following reason: if the main task and subtask priority levels are the same, a task
transition to the main task occurs during subtask END processing, and an illegal task status then
occurs when the main task attempts to start a subtask.
Therefore, in order to properly execute the program, the subtask priority level must be set higher
than that of the main task. This prevents a task transition condition from occurring during execution
of the EXIT TASK command.
In the sample program shown below, the priority level of task 1 (main task) is set as 32, and the
priority level of task 2 is set as 31 (the lower the value, the higher the priority).
SAMPLE
FLAG1 = 0
*MAIN_TASK:
IF FLAG1=0 THEN
FLAG1 = 1
START <SUB_PGM>,T2,31 ········· <SUB_PGM> is started as task 2
at the priority level of 31.
ENDIF
GOTO *MAIN_TASK
HALTALL
Program name:SUB_PGM
'==============
'
TASK2
'==============
*TASK2:
DRIVE(1,P1)
WAIT ARM(1)
DRIVE(1,P2)
WAIT ARM(1)
FLAG1 = 0
EXIT TASK
Содержание SCARA YRCX Series
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