R8C/13 Group
10.1 Interrupt Overview
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 Nos. 4 to 31 are assigned
to peripheral function interrupts, the same interrupt routine as for peripheral function interrupts 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.
Rev.1.20 Jan 27, 2006 page 48 of 205
REJ09B0111-0120
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