LSIS Master-K K1000S - Interrupt Processing

Chapter 4 CPU modules MASTER-K
4-11
4.3.3 Interrupt processing
When an interrupt occurs, the CPU module will stop the current operation and execute
the corresponding interrupt routine. After finish the interrupt routine, the CPU resume the
sequence program from the stopped step.
MASTER-K series provides 2 types of interrupt. The TDI (Time driven interrupt) occurs
with the constant period, and PDI (Process driven interrupt) occurs with the status of
external input.
Before to use interrupt function in sequence program, the parameter setting should be
done properly. Then the corresponding interrupt routine should be written after END
instruction. (Refer chapter 4 for details) If interrupt routines are not matched with
parameter settings, an error occurs and the operation of CPU will be stopped.
To execute an interrupt routine, use the EI instruction to enable the corresponding
interrupt. The interrupt routine is not executed if an interrupt factor occurs before
execution of an EI instruction. Once an interrupt is enabled with EI instruction, it keeps
the enabled status until DI instruction is executed to disable the interrupt. When a CPU is
turned to RUN mode, all interrupts are disabled by default.
When multiple interrupt factors occur simultaneously, interrupt routines are executed
according to the priority given to the each interrupt. If an interrupt factor that has higher
priority occurs while other interrupt that has lower priority are executing, the interrupt
routine of lower priority will be stopped and the interrupt of higher priority will be executed
first. The following figure shows how a CPU handles multiple interrupts.
Program starts
Interrupt 2 occurs
Stop main program and execute interrupt
routine 2
Interrupt 1 occurs (higher priority)
Stop routine 2 and run routine 1
Finish routine 1 and return to routine2
Scan Program
Interrupt routine 1
Interrupt routine 2
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4
Finish routine 2 and return to main
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