H8SSLASH2225 datasheet(233/1071 Pages) RENESAS

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Section 5 Interrupt Controller

Rev. 5.00 Aug 08, 2006 page 147 of 982

REJ09B0054-0500

5.5.3

Interrupt Control Mode 2

Eight-level masking is implemented for IRQ interrupts, and on-chip peripheral module interrupts

by comparing the interrupt mask level set by bits I2 to I0 of EXR in the CPU with IPR.

Figure 5.6 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. When interrupt requests are sent to the interrupt controller, the interrupt with the highest

priority according to the interrupt priority levels set in IPR is selected, and lower-priority

interrupt requests are held pending. If a number of interrupt requests with the same priority are

generated at the same time, the interrupt request with the highest priority according to the

priority system shown in table 5.2 is selected.

3. Next, the priority of the selected interrupt request is compared with the interrupt mask level set

in EXR. An interrupt request with a priority no higher than the mask level set at that time is

held pending, and only an interrupt request with a priority higher than the interrupt mask level

is accepted.

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, CCR, and EXR 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. The T bit in EXR is cleared to 0. The interrupt mask level is rewritten with the priority level of

the accepted interrupt.

If the accepted interrupt is NMI, the interrupt mask level is set to H'7.

7. The CPU generates a vector address for the accepted interrupt and starts execution of the

interrupt handling routine at the address indicated by the contents of the vector address in the

vector table.

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