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M16C/62P Group (M16C/62P, M16C/62PT)
24.6.6 Rewrite the Interrupt Control Register
(a) 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.
(b) 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 re-
quested). Therefore, be sure to use the MOV instruction to clear the IR bit.
(c) 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 (b) for details about rewrite the interrupt control registers in the sample
program fragments.)
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, owing to the effects of 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
AND.B
NOP
NOP
FSET
The number of NOP instruction is as follows.
PM20=1(1 wait) : 2, PM20=0(2 wait) : 3, when using HOLD function : 4.
Example 2:Using the dummy read to keep the FSET instruction waiting
INT_SWITCH2:
FCLR
AND.B
R
e
. v
2
3 .
0
S
e
p
0
, 1
2
0
0
4
R
E
J
0
9
B
0
1
8
5
0 -
2
3
0
Z
I
; Disable interrupts.
#00h, 0055h
; Set the TA0IC register to "00
;
I
; Enable interrupts.
I
; Disable interrupts.
#00h, 0055h
; Set the TA0IC register to "00
page 333
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24. Usage Precaution
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