Datasheet

Section 5 Interrupt Controller
Rev.6.00 Mar. 18, 2009 Page 108 of 980
REJ09B0050-0600
5.6 Interrupt Control Modes and Interrupt Operation
The interrupt controller has two modes: interrupt control mode 0 and interrupt control mode 2.
Interrupt operations differ depending on the interrupt control mode. The interrupt control mode is
selected by INTCR. Table 5.3 shows the differences between interrupt control mode 0 and
interrupt control mode 2.
Table 5.3 Interrupt Control Modes
Interrupt Priority Setting Interrupt
Control Mode Registers Mask Bits Description
0 Default I The priorities of interrupt sources are fixed at the
default settings.
Interrupt sources except for NMI is masked by
the I bit.
2 IPR I2 to I0 8 priority levels except for NMI can be set with
IPR.
8-level interrupt mask control is performed by
bits I2 to I0.
5.6.1 Interrupt Control Mode 0
In interrupt control mode 0, interrupt requests except for NMI is masked by the I bit of CCR in the
CPU. Figure 5.3 shows a flowchart of the interrupt acceptance operation in this case.
1. If an interrupt source occurs when the corresponding interrupt enable bit is set to 1, an
interrupt request is sent to the interrupt controller.
2. If the I bit is set to 1, only an NMI interrupt is accepted, and other interrupt requests are held
pending. If the I bit is cleared, an interrupt request is accepted.
3. Interrupt requests are sent to the interrupt controller, the highest-ranked interrupt according to
the priority system is accepted, and other interrupt requests are held pending.
4. When the CPU accepts an interrupt request, it starts interrupt exception handling after
execution of the current instruction has been completed.
5. The PC and CCR are saved to the stack area by interrupt exception handling. The PC saved on
the stack shows the address of the first instruction to be executed after returning from the
interrupt handling routine.
6. Next, the I bit in CCR is set to 1. This masks all interrupts except NMI.