HD64F3028F25 Datasheet, PDF (137/925 Pages) Renesas Technology Corp – Hardware Manual Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Series

5.5 Usage Notes
5.5.1 Contention between Interrupt and Interrupt-Disabling Instruction
When an instruction clears an interrupt enable bit to 0 to disable the interrupt, the interrupt is not
disabled until after execution of the instruction is completed. If an interrupt occurs while a BCLR,
MOV, or other instruction is being executed to clear its interrupt enable bit to 0, at the instant
when execution of the instruction ends the interrupt is still enabled, so its interrupt exception
handling is carried out. If a higher-priority interrupt is also requested, however, interrupt exception
handling for the higher-priority interrupt is carried out, and the lower-priority interrupt is ignored.
This also applies to the clearing of an interrupt flag to 0.
Figure 5.8 shows an example in which an IMIEA bit is cleared to 0 in the 16-bit timer's TISRA
register.
φ
Internal
address bus
Internal
write signal
IMIEA
TISRA write cycle by CPU
TISRA address
IMIA exception handling
IMIA
IMFA interrupt
signal
Figure 5.8 Contention between Interrupt and Interrupt-Disabling Instruction
This type of contention will not occur if the interrupt is masked when the interrupt enable bit or
flag is cleared to 0.
Rev. 2.00, 09/03, page 105 of 890