M16C80 Datasheet, PDF (68/358 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/80 SERIES

M16C/80 Group
9. Interrupt Outline
9.2 Software Interrupts
Software interrupts are generated by some instruction that generates an interrupt request when ex-
ecuted. Software interrupts are nonmaskable interrupts.
(1) Undefined-instruction interrupt
This interrupt occurs when the UND instruction is executed.
(2) Overflow interrupt
This interrupt occurs if the INTO instruction is executed when the O flag is 1.
The following lists the instructions that cause the O flag to change:
ABS, ADC, ADCF, ADD, ADDX, CMP, CMPX, DIV, DIVU, DIVX, NEG, RMPA, SBB, SCMPU, SHA,
SUB, SUBX
(3) BRK interrupt
This interrupt occurs when the BRK instruction is executed.
(4) BRK2 interrupt
This interrupt occurs when the BRK2 instruction is executed. This interrupt is used exclusively for
debugger purposes. You normally do not need to use this interrupt.
(5) INT instruction interrupt
This interrupt occurs when the INT instruction is executed after specifying a software interrupt number
from 0 to 63. Note that software interrupt numbers 0 to 43 are assigned to peripheral I/O interrupts.
This means that by executing the INT instruction, you can execute the same interrupt routine as used
in peripheral I/O interrupts.
The stack pointer used in INT instruction interrupt varies depending on the software interrupt number.
For software interrupt numbers 0 to 31, the U flag is saved when an interrupt occurs and the U flag is
cleared to 0 to choose the interrupt stack pointer (ISP) before executing the interrupt sequence. The
previous U flag before the interrupt occurred is restored when control returns from the interrupt rou-
tine. For software interrupt numbers 32 to 63, such stack pointer switchover does not occur.
However, in peripheral I/O interrupts, the U flag is saved when an interrupt occurs and the U flag is
cleared to 0 to choose ISP.
Therefore movement of U flag is different by peripheral I/O interrupt or INT instruction in software
interrupt number 32 to 43.
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