R8C datasheet(44/199 Pages) RENESAS

44 / 199 page

R8C/10 Group

Rev.1.20 Jan 27, 2006

page 34 of 180

REJ09B0019-0120

10.1.2 Software Interrupts

A software interrupt occurs when executing certain instructions. Software interrupts are non-

maskable interrupts.

• Undefined Instruction Interrupt

An undefined instruction interrupt occurs when executing the UND instruction.

• Overflow Interrupt

An overflow interrupt occurs when executing the INTO instruction with the O flag set to “1” (the

operation resulted in an overflow). The following are instructions whose O flag changes by arith-

metic:

ABS, ADC, ADCF, ADD, CMP, DIV, DIVU, DIVX, NEG, RMPA, SBB, SHA, SUB

• BRK Interrupt

A BRK interrupt occurs when executing the BRK instruction.

• INT Instruction Interrupt

An INT instruction interrupt occurs when executing the INT instruction. Software interrupt numbers 0

to 63 can be specified for the INT instruction. Because software interrupt numbers 4 to 31 are as-

signed to peripheral function interrupts, the same interrupt routine as for peripheral function inter-

rupts can be executed by executing the INT instruction.

In software interrupt numbers 0 to 31, the U flag is saved to the stack during instruction execution

and is cleared to “0” (ISP selected) before executing an interrupt sequence. The U flag is restored

from the stack when returning from the interrupt routine. In software interrupt numbers 32 to 63, the

U flag does not change state during instruction execution, and the SP then selected is used.

10.1 Interrupt Overview

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