Datasheet

Section 5 Interrupt Controller

Rev.7.00 Dec. 24, 2008 Page 103 of 698

REJ09B0074-0700

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 SYSCR. Table 5.3 shows the differences between interrupt control mode 0 and

interrupt control mode 2.

Table 5.3 Interrupt Control Modes

Interrupt

Control Mode

Priority Setting

Interrupt Mask

Bits Description

0 Default I The priority of interrupt sources are fixed at

the default settings.

Interrupt sources except for NMI is marked by

the I bit.

2 IPR I2 to I0 8-level interrupt mask control is performed by

bits I2 to I0.

8 priority levels other than NMI can be set with

IPR.

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 5.4 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.