M16CSLASH29 datasheet(452/499 Pages) RENESAS

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22. Usage Notes

page 428

22.4.6 Rewrite the Interrupt Control Register

(1) The interrupt control register for any interrupt should be modified in places where no requests for that

interrupt may occur. Otherwise, disable the interrupt before rewriting the interrupt control register.

(2) To rewrite the interrupt control register for any interrupt after disabling that interrupt, be careful with the

instruction to be used.

Changing any bit other than the IR bit

If while executing an instruction, a request for an interrupt controlled by the register being modified

occurs, the IR bit in the register may not be set to 1 (interrupt requested), with the result that the

interrupt request is ignored. If such a situation presents a problem, use the instructions shown below

to modify the register.

Usable instructions: AND, OR, BCLR, BSET

Changing the IR bit

Depending on the instruction used, the IR bit may not always be cleared to 0 (interrupt not requested).

Therefore, be sure to use the MOV instruction to clear the IR bit.

(3) When using the I flag to disable an interrupt, refer to the sample program fragments shown below as

you set the I flag. (Refer to (2) for details about rewrite the interrupt control registers in the sample

program fragments.)

22.4.7 Watchdog Timer Interrupt

Initialize the watchdog timer after the watchdog timer interrupt occurs.

Examples 1 through 3 show how to prevent the I flag from being set to 1 (interrupts enabled) before the

interrupt control register is rewrited, due to the internal bus and the instruction queue buffer.

Example 1: Using the NOP instruction to keep the program waiting until the

interrupt control register is modified

INT_SWITCH1:

FCLR

; Disable interrupts

AND.B

#00h, 0055h

;Set the TA0IC register to 0016

NOP

;

NOP

FSET

; Enable interrupts

The number of NOP instruction is as follows.

PM20 = 1 (1 wait) : 2, PM20 = 0 (2 waits): 3

Example 2:Using the dummy read to keep the FSET instruction waiting

INT_SWITCH2:

FCLR

; Disable interrupts

AND.B

#00h, 0055h

; Set the TA0IC register to 0016

MOV.W MEM, R0

; Dummy read

FSET

; Enable interrupts

Example 3:Using the POPC instruction to changing the I flag

INT_SWITCH3:

PUSHC FLG

FCLR

; Disable interrupts

AND.B

#00h, 0055h

; Set the TA0IC register to 0016

POPC

FLG

; Enable interrupts

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