Mitsubishi microcomputers
M16C / 61 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Precautions for Interrupts
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)
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Figure 1.13.12. 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
; Disable interrupts.
AND.B #00h, 0055h ; Clear TA0IC int. priority level and int. request bit.
NOP
NOP
FSET
; Four NOP instructions are required when using HOLD function.
; Enable interrupts.
I
Example 2:
INT_SWITCH2:
FCLR
I
; Disable interrupts.
AND.B #00h, 0055h ; Clear TA0IC int. priority level and int. request bit.
MOV.W MEM, R0
; Dummy read.
; Enable interrupts.
FSET
I
Example 3:
INT_SWITCH3:
PUSHC FLG
; Push Flag register onto stack
; Disable interrupts.
FCLR
I
AND.B #00h, 0055h ; Clear TA0IC int. priority level and int. request bit.
POPC FLG ; 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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MITSUBISHI [ Mitsubishi Group ]
