SH7041A datasheet(150/923 Pages) RENESAS

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6.4

Interrupt Operation

6.4.1

Interrupt Sequence

The sequence of interrupt operations is explained below. Figure 6.3 is a flowchart of the

operations.

1. The interrupt request sources send interrupt request signals to the interrupt controller.

2. The interrupt controller selects the highest priority interrupt in the interrupt requests sent,

following the priority levels set in interrupt priority level setting registers A–H (IPRA–IPRH).

Lower-priority interrupts are ignored. They are held pending until interrupt requests designated

as edge-detect type are accepted. For IRQ interrupts, however, withdrawal is possible by

accessing the IRQ status register (ISR). See section 6.2.3, IRQ Interrupts, for details. Interrupts

held pending due to edge detection are cleared by a power-on reset or a manual reset. If two of

these interrupts have the same priority level or if multiple interrupts occur within a single

module, the interrupt with the highest default priority or the highest priority within its IPR

setting range (as indicated in table 6.3) is selected.

3. The interrupt controller compares the priority level of the selected interrupt request with the

interrupt mask bits (I3–I0) in the CPU’s status register (SR). If the request priority level is

equal to or less than the level set in I3–I0, the request is ignored. If the request priority level is

higher than the level in bits I3–I0, the interrupt controller accepts the interrupt and sends an

interrupt request signal to the CPU.

4. When the interrupt controller accepts an interrupt, a low level is output from the

IRQOUT pin.

5. The CPU detects the interrupt request sent from the interrupt controller when it decodes the

next instruction to be executed. Instead of executing the decoded instruction, the CPU starts

interrupt exception processing (figure 6.4).

6. SR and PC are saved onto the stack.

7. The priority level of the accepted interrupt is copied to the interrupt mask level bits (I3–I0) in

the status register (SR).

8. When the accepted interrupt is sensed by level or is from an on-chip peripheral module, a high

level is output from the

IRQOUT pin. When the accepted interrupt is sensed by edge, a high

level is output from the

IRQOUT pin at the point when the CPU starts interrupt exception

processing instead of instruction execution as noted in (5) above. However, if the interrupt

controller accepts an interrupt with a higher priority than one it is in the midst of accepting, the

IRQOUT pin will remain low level.

9. The CPU reads the start address of the exception service routine from the exception vector

table for the accepted interrupt, jumps to that address, and starts executing the program there.

This jump is not a delay branch.

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