HD64F7047 datasheet(106/764 Pages) RENESAS

106 / 764 page

Rev. 2.00, 09/04, page 66 of 720

5.4.2

Interrupt Priority Level

The interrupt priority is predetermined. When multiple interrupts occur simultaneously

(overlapped interruptions), the interrupt controller (INTC) determines their relative priorities and

starts the exception processing according to the results.

The priority of interrupts is expressed as priority levels 0 to 16, with priority 0 the lowest and

priority 16 the highest. The NMI interrupt has priority 16 and cannot be masked, so it is always

accepted. The priority level of user break interrupt and H-UDI is 15. IRQ interrupts and on-chip

peripheral module interrupt priority levels can be set freely using the INTC’s interrupt priority

level setting registers A, D to I, and K (IPRA, IPRD to IPRI, and IPRK) as shown in table 5.8. The

priority levels that can be set are 0 to 15. Level 16 cannot be set. See section 6.3.4, Interrupt

Priority Registers A, D to I, K (IPRA, IPRD to IPRI, IPRK), for more information on IPRA to

IPRK.

Table 5.8

Interrupt Priority

Type

Priority Level

Comment

NMI

Fixed priority level. Cannot be masked.

User break

Fixed priority level.

H-UDI

Fixed priority level.

IRQ

On-chip peripheral module

0 to 15

Set with interrupt priority level setting registers

A through K (IPRA to IPRK).

5.4.3

Interrupt Exception Processing

When an interrupt occurs, the interrupt controller (INTC) ascertains its priority level. NMI is

always accepted, but other interrupts are only accepted if they have a priority level higher than the

priority level set in the interrupt mask bits (I3 to I0) of the status register (SR).

When an interrupt is accepted, exception processing begins. In interrupt exception processing, the

CPU saves SR and the program counter (PC) to the stack. The priority level value of the accepted

interrupt is written to SR bits I3 to I0. For NMI, however, the priority level is 16, but the value set

in I3 to I0 is H'F (level 15). Next, the start address of the exception service routine is fetched from

the exception processing vector table for the accepted interrupt, that address is jumped to and

execution begins. See section 6.6, Interrupt Operation, for more information on the interrupt

exception processing.

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