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1 PROGRAM EXECUTION
1.5 Program Type
Processing at startup of interrupt program
Processing is as follows when an interrupt program is started up.
• Purge/restore of index registers (Z, LZ)
■Purge/restore of index registers (Z, LZ)
When an interrupt program is started up, the values of the index registers (Z, LZ) in the currently executing program are
purged, and those values are handed over to the interrupt program. Then, when an interrupt program is terminated, the
purged values are restored to the currently executing program.
Precautions
The precautions for interrupt programs are explained below.
■Restrictions in programming
• The PLS/PLF instructions execute OFF processing at the scan following instruction execution. ON devices remain ON until
the interrupt program runs again and the instruction is executed.
• Only a routine timer can be used in an interrupt program. Timers (T, ST) cannot be used.
■Splitting of data
Processing may be interrupted during instruction execution and an interrupt programs can be executed. Accordingly, splitting
of data might occur if the same devices are used by both the interrupt program and the program that is aborted by the
interrupt. Implement the following preventive measure.
• Set instructions that will result in inconsistencies if interrupted to "interrupt disabled" using the DI instruction.
• When using bit data, ensure that the same bit data is not used by both the interrupt program and the program that is
aborted by the interrupt.
■Interrupt precision is not improved
If interrupt precision is not improved, this might be remedied by implementing the following:
• Give higher priority to the interrupt that needs higher precision.
• Use an interrupt pointer with high interrupt priority order.
• Recheck the section of interruption disabled.