M16C30_02 Datasheet, PDF (64/178 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Precautions for Interrupts
Mitsubishi microcomputers
M16C / 30 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
(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 changing an interrupt control register in a sate of interrupts being disabled, please read the
following precautions on instructions used before changing the register.
Changing a non-interrupt request bit
If an interrupt request for an interrupt control register is generated during an instruction to rewrite the
register is being executed, there is a case that the interrupt request bit is not set and consequently the
interrupt is ignored. This will depend on the instruction. If this creates problems, use the below instruc-
tions to change the register.
Instructions : AND, OR, BCLR, BSET
Changing the interrupt request bit
When attempting to clear the interrupt request bit of an interrupt control register, the interrupt request bit
is not cleared sometimes. This will depend on the instruction. If this creates problems, use the below
instructions to change the register.
Instructions : MOV
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