4518 datasheet(22/160 Pages) RENESAS

22 / 160 page

Rev.3.01

2005.06.15

page 22 of 157

REJ03B0008-0301

4518 Group

(4) Internal state during an interrupt

The internal state of the microcomputer during an interrupt is as fol-

lows (Figure 14).

• Program counter (PC)

An interrupt address is set in program counter. The address to be

executed when returning to the main routine is automatically

stored in the stack register (SK).

• Interrupt enable flag (INTE)

INTE flag is cleared to “0” so that interrupts are disabled.

• Interrupt request flag

Only the request flag for the current interrupt source is cleared to

“0.”

• Data pointer, carry flag, skip flag, registers A and B

The contents of these registers and flags are stored automatically

in the interrupt stack register (SDP).

(5) Interrupt processing

When an interrupt occurs, a program at an interrupt address is ex-

ecuted after branching a data store sequence to stack register.

Write the branch instruction to an interrupt service routine at an in-

terrupt address.

Use the RTI instruction to return from an interrupt service routine.

Interrupt enabled by executing the EI instruction is performed after

executing 1 instruction (just after the next instruction is executed).

Accordingly, when the EI instruction is executed just before the RTI

instruction, interrupts are enabled after returning the main routine.

(Refer to Figure 13)

Fig. 13 Program example of interrupt processing

• Program counter (PC)

............................................................... Each interrupt address

• Stack register (SK)

....................................................................................................

• Interrupt enable flag (INTE)

.................................................................. 0 (Interrupt disabled)

• Interrupt request flag (only the flag for the current interrupt

source) ................................................................................... 0

• Data pointer, carry flag, registers A and B, skip flag

........ Stored in the interrupt stack register (SDP) automatically

The address of main routine to be

executed when returning

Fig. 15 Interrupt system diagram

Fig. 14 Internal state when interrupt occurs

RTI

Interrupt

service routine

Interrupt

occurs

Interrupt is

enabled

Main

routine

: Interrupt enabled state

: Interrupt disabled state

•

V11

EXF0

V10

Address 2

in page 1

Address 4

in page 1

Address 0

in page 1

Timer 1

underflow

Timer 2

underflow

T1F

V12

Request flag

(state retained)

Enable bit

Enable flag

Activated

condition

V13

Address 6

in page 1

A/D conversion

completed

INTE

ADF

T2F

V20

T3F

V21

SIOF

V23

T4F

V22

INT0 pin interrupt

waveform input

Timer 3

underflow

Timer 4

underflow

Serial I/O

transmit/

receive

completed

INT1 pin interrupt

waveform input

EXF1

Address 8

in page 1

Address A

in page 1

Address C

in page 1

Address E

in page 1

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