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2-14
CPU
2.5 Interrupts
2.5.1 Overview of Interrupts
The most important key to real-time control is the ability to shift quickly to interrupt handler processing.
If an interrupt is generated during the execution of an instruction that requires multiple cycles for execution
(multiplication or division instructions, for example), interrupt response is improved by aborting the execution of
the instruction and immediately accepting the interrupt. After control returns from the interrupt processing program,
the aborted instruction is re-executed.
In addition, by minimizing the resources saved to memory to just the 6 bytes of the PC and the PSW when an
interrupt is generated, the speed of interrupt processing is improved, as is the flexibility of software control.
Furthermore, fast response and optimal program allocation are possible by placing interrupt processing programs at
different addresses for each interrupt level.
This microcontroller has the interrupts shown below. When any of these interrupts occurs, control is shifted to the
appropriate processing program in accordance with the cause.
Reset interrupt
Non-maskable interrupt Priority ranking
Level interrupt n (n = 0 to 6)
Fig. 2-5-1 shows an overview of the interrupt system. This microcontroller is equipped with 19 interrupt group
control blocks outside the CPU, and controls the interrupts of each group separately. Each interrupt group control
block can accept up to 4 interrupt requests. This allows the controller to support to 38 interrupt factors, providing it
with high expandability and enabling flexible ASIC support.
Except for the reset interrupt, all interrupts from the timer and other peripheral circuits and external pin interrupts
are registered in the interrupt group control blocks. Then, the interrupt requests which pass the interrupt priority
level (level 0 to 6) set in the interrupt group control blocks are output to the CPU. Groups 0 is assigned to non-
maskable interrupts only.
Fig. 2-5-1 Overview of the Interrupt System
➤
Interrupt controller (INTC)
4
Group 0
3 factors are allocated to this group: external pin non-maskable
interrupt, watchdog timer overflow interrupt and system error
interrupt. The remaining factor is reserved.
4
4
Group 2
Group 19
71
Interrupt group control
Interrupt
Interrupt
Interrupt
8 external pin interrupts as well as timer, serial
and other peripheral interrupts are assigned.
Interrupt group control
CPU
Interrupt group control
Non-maskable interrupts
External interrupts