M306V2EEFS datasheet(56/271 Pages) RENESAS

56 / 271 page

Rev.1.40

Oct 06, 2004 page 56 of 269

M306V2ME-XXXFP, M306V2EEFP

2.7.9 Rewrite Interrupt Control Register

To rewrite the interrupt control register, do so at a point that does not generate the interrupt request for

that register. If there is possibility of the interrupt request occur, rewrite the interrupt control register after

the interrupt is disabled. The program examples are described as follow:

When a instruction to rewrite the interrupt control register is executed but the interrupt is disabled, the

interrupt request bit is not set sometimes even if the interrupt request for that register has been gener-

ated. This will depend on the instruction. If this creates problems, use the below instructions to change

the register.

Instructions : AND, OR, BCLR, BSET

Example 1:

INT_SWITCH1:

FCLR

; Disable interrupts.

AND.B

#00h, 0055h

; Clear TA0IC int. priority level and int. request bit.

NOP

; Four NOP instructions are required when using HOLD function.

NOP

FSET

; Enable interrupts.

Example 2:

INT_SWITCH2:

FCLR

; Disable interrupts.

AND.B

#00h, 0055h

; Clear TA0IC int. priority level and int. request bit.

MOV.W MEM, R0

; Dummy read.

FSET

; Enable interrupts.

Example 3:

INT_SWITCH3:

PUSHC FLG

; Push Flag register onto stack

FCLR

; Disable interrupts.

AND.B

#00h, 0055h

; Clear TA0IC int. priority level and int. request bit.

POPC

FLG

; Enable interrupts.

The reason why two NOP instructions (four when using the HOLD function) or dummy read are inserted

before FSET I in Examples 1 and 2 is to prevent the interrupt enable flag I from being set before the

interrupt control register is rewritten due to effects of the instruction queue.

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