M16C62M Datasheet, PDF (19/25 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Usage precaution
Mitsubishi microcomputers
M16C / 62M (80-pin version) Group
(Low voltage version)
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
(4) External interrupt
_______
________
• When the polarity of the INT0 to INT2 pins is changed, the interrupt request bit is sometimes set
to "1". After changing the polarity, set the interrupt request bit to "0".
(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:
Example 1:
INT_SWITCH1:
FCLR I
AND.B #00h, 0055h
NOP
NOP
FSET I
; Disable interrupts.
; Clear TA0IC int. priority level and int. request bit.
; Enable interrupts.
Example 2:
INT_SWITCH2:
FCLR I
AND.B #00h, 0055h
MOV.W MEM, R0
FSET I
; Disable interrupts.
; Clear TA0IC int. priority level and int. request bit.
; Dummy read.
; Enable interrupts.
Example 3:
INT_SWITCH3:
PUSHC FLG
FCLR I
AND.B #00h, 0055h
POPC FLG
; Push Flag register onto stack
; Disable interrupts.
; Clear TA0IC int. priority level and int. request bit.
; Enable interrupts.
The reason why two NOP instructions 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.
• 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
Noise
(1) Insert bypass capacitor between VCC and VSS pin for noise and latch up countermeasure.
• Insert bypass capacitor (about 0.1 µF) and connect short and wide line between VCC and VSS
lines.
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