
R8C/14 Group, R8C/15 Group 20. Precautions
Rev.2.10 Jan 19, 2006 Page 238 of 253
REJ09B0164-0210
20.2.6 Changing Interrupt Control Register
(a) Each interrupt control register can only be changed while interrupt requests corresponding to
that register are not generated. If interrupt requests may be generated, disable the interrupts
before changing 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”.
(c) When disabling interrupts using the I flag, set the I flag according to the following sample
programs. 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 TXIC 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 TXIC 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 TXIC register to “00h”
POPC FLG ; Enable interrupts
Kommentare zu diesen Handbüchern