M16C6K9 Datasheet, PDF (244/292 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

M16C/6K9 Group
Usage precaution
(2) Setting the stack pointer
• The value of the stack pointer immediately after reset is initialized to 000016. Accepting an interrupt
before setting a value in the stack pointer may become a factor of runaway. Be sure to set a value in the
stack pointer before accepting an interrupt.
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When using the NMI interrupt, initialize the stack point at the beginning of a program. Concerning the first
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instruction immediately after reset, generating any interrupts including the NMI interrupt is prohibited.
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(3) The NMI interrupt
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• As for the NMI interrupt pin, an interrupt cannot be disabled. Connect it to the VCC pin via a resistor
(pull-up) if unused. Be sure to work on it.
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• Do not get either into stop mode with the NMI pin set to “L”.
(4) External interrupt
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• When the polarity of the INT0 to INT11 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.
; 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 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 the by-pass condencer to the Vcc-Vss line for preventing a noise and latch-up. Connect the by -pass
condencer (about 0.1µF) between Vcc pin and Vss pin. It is distance must be shortest rather sicker line.
Rev.1.00 Jun 06, 2003 page 244 of 290