![](http://datasheet.mmic.net.cn/280000/M30612MC-211FP_datasheet_16083280/M30612MC-211FP_140.png)
Mitsubishi microcomputers
M16C / 61 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Usage precaution
140
(4) External interrupt
When the polarity of the INT
0
to INT
2
pins is changed, the interrupt request bit is sometimes set to
"1". After changing the polarity, set the interrupt request bit to "0".
Example 1:
INT_SWITCH1:
FCLR
AND.B
NOP
NOP
FSET
I
#00h, 0055h
; Disable interrupts.
; Clear TA0IC int. priority level and int. request bit.
; Four NOP instructions are required when using HOLD function.
I
; Enable interrupts.
Example 2:
INT_SWITCH2:
FCLR
AND.B
MOV.W MEM, R0
FSET
I
#00h, 0055h
; Disable interrupts.
; Clear TA0IC int. priority level and int. request bit.
; Dummy read.
; Enable interrupts.
I
Example 3:
INT_SWITCH3:
PUSHC FLG
FCLR
AND.B
POPC
; Push Flag register onto stack
; Disable interrupts.
; Clear TA0IC int. priority level and int. request bit.
; Enable interrupts.
I
#00h, 0055h
FLG
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.
(5) Rewrite the 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 generated. This will depend on the instruction. If this creates problems, use the below
instructions to change the register.
Instructions : AND, OR, BCLR, BSET
(3) The NMI interrupt
As for the NMI interrupt pin, an interrupt cannot be disabled. Connect it to the V
CC
pin via a
resistor (pull-up) if unused. Be sure to work on it.
Do not get either into stop mode or into wait mode with the NMI pin set to “L”.