Omron CS1G/H-CPUxxH Instructions Manual page 789

Interrupt Control Instructions
Main program
execution
Scheduled interrupt
task execution
Precautions
768
5. After scheduled interrupt processing has begun, the scheduled time inter-
val can be changed by executing MSKS(690). In this case, the time interval
is changed from 100 ms to 200 ms.
6. Scheduled interrupt processing is disabled by executing MSKS(690) with
a time interval of 0000.
The following timing chart shows the operation of the example listed above.
1, 2
3 3 3
20 ms 100 ms 100 ms
Be sure that the scheduled time interval is longer than the time required to
execute the scheduled interrupt task. If the scheduled time interval is too
short, the interrupt task will be executed continuously and a Cycle Time Too
Long Error will occur. (A long scheduled interrupt task can seriously affect the
main program's overall execution time.)
The scheduled interrupt is executed after the specified time interval plus the
execution time for one instruction. Normally the time required to execute one
instruction is negligible, but it can cause errors when instructions that take a
long time are being used; it can also cause errors in timers (TIM and TIMH)
and data tracing. Be particularly careful when the scheduled time interval
units are set to 0.5 ms or 1 ms in the PLC Setup.
Interrupts are accepted even while one instruction is being executed. There-
fore, if an interrupt is accepted while an instruction requiring a long processing
time is being executed, correct processing results may not be obtained
because both the interrupt task and the instruction may access the same
data. In such a case, use DI(693) and EI(694) to disable and enable the inter-
rupt.
4 5
3 3 3 3
50 ms 100 ms100 ms 200 ms
Interrupt task
Interrupt
during
execution
Interrupts
disabled
Section 3-20
6
3