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R8C/20 Group, R8C/21 Group 21. Usage Notes

Rev.2.00 Aug 27, 2008 Page 431 of 458

REJ09B0250-0200

21.2.5 Changing Interrupt Control Register Contents

(a) Each interrupt control register can only be changed while interrupt requests corresponding to that

the interrupt control register.

(b) When changing any interrupt control register after disabling interrupts, be careful with the instructions

to be used.

When changing any bit other than IR bit

If an interrupt request corresponding to that register is generated while executing the instruction, the IR

bit may not be set to 1 (interrupt requested), and the interrupt request may be ignored. If this causes a

problem, use the following instructions to change the register.

Instructions to use: AND, OR, BCLR, BSET

When changing IR bit

If the IR bit is set to 0 (interrupt not requested), it may not be set to 0 depending on the instruction to be

used. Therefore, use the MOV instruction to set the IR bit to 0.

Refer to (b) for the change of interrupt control registers in the sample programs.

Sample programs 1 to 3 are preventing the I flag from being set to 1 (interrupt enables) before changing the

interrupt control register for reasons of the internal bus or the instruction queue buffer.

Example 1: Use NOP instructions to prevent I flag being set to 1 before interrupt control register is

changed

INT_SWITCH1:

FCLR I ; Disable interrupts

AND.B #00H,0056H ; Set TRAIC register to 00h

NOP ;

NOP

FSET I ; Enable interrupts

Example 2: Use dummy read to have FSET instruction wait

INT_SWITCH2:

FCLR I ; Disable interrupts

AND.B #00H,0056H ; Set TRAIC register to 00h

MOV.W MEM,R0 ; Dummy read

FSET I ; Enable interrupts

Example 3: Use POPC instruction to change I flag

INT_SWITCH3:

PUSHC FLG

FCLR I ; Disable interrupts

AND.B #00H,0056H ; Set TRAIC register to 00h

POPC FLG ; Enable interrupts

Renesas R8C/20 User Manual

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