HMS81032TL datasheet(54/77 Pages) HYNIX

54 / 77 page

HMS81004E/08E/16E/24E/32E

JUNE 2001 Ver 1.00

Figure 14-4 Timing chart of Interrupt Acceptance and Interrupt Return Instruction

A interrupt request is not accepted until the I-flag is set to “1”

even if a requested interrupt has higher priority than that of the

current interrupt being serviced.

When nested interrupt service is required, the I-flag should be set

to “1” by “EI” instruction in the interrupt service program. In this

case, acceptable interrupt sources are selectively enabled by the

individual interrupt enable flags.

Saving/Restoring General-purpose Register

During interrupt acceptance processing, the program counter and

the program status word are automatically saved on the stack, but

accumulator and other registers are not saved itself. These regis-

ters are saved by the software if necessary. Also, when multiple

interrupt services are nested, it is necessary to avoid using the

same data memory area for saving registers.

The following method is used to save/restore the general-purpose

registers.

Example: Register save using push and pop instructions

General-purpose register save/restore using push and pop instruc-

tions;

V.L.

System clock

Address Bus

SP-1

SP-2

V.H.

New PC

V.L.

Data Bus

Not used

PCH

PCL

PSW

ADL

OP code

ADH

Instruction Fetch

Internal Read

Internal Write

Interrupt Processing Step

Interrupt Service Task

V.L. and V.H. are vector addresses.

ADL and ADH are start addresses of interrupt service routine as vector contents.

External Interrupt1

012H

0E3H

0FFF8H

0FFF9H

0EH

2EH

0E312H

0E313H

Entry Address

Correspondence between vector table address for Exteranl Interrupt1

and the entry address of the interrupt service program.

Vector Table Address

INTxx:

PUSH

;SAVE ACC.

;SAVE X REG.

;SAVE Y REG.

interrupt processing

POP

RETI

;RESTORE Y REG.

;RESTORE X REG.

;RESTORE ACC.

;RETURN

main task

interrupt

service task

saving

registers

restoring

registers

acceptance of

interrupt

interrupt return

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