M16C62A Datasheet, PDF (56/242 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Precautions for Interrupts
Mitsubishi microcomputers
M16C / 62A Group (80-pin)
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Clear the interrupt enable flag to “0”
(Disable interrupt)
Set the interrupt priority level to level 0
(Disable INTi interrupt)
Set the polarity select bit
Clear the interrupt request bit to “0”
Set the interrupt priority level to level 1 to 7
(Enable the accepting of INTi interrupt request)
Set the interrupt enable flag to “1”
(Enable interrupt)
Note: Execute the setting above individually. Don't execute two or
more settings at once(by one instruction).
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Figure 1.10.13. Switching condition of INT interrupt request
(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.
; Four NOP instructions are required when using HOLD function.
; 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 (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.
• 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
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