9. Interrupts
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9.1.1 Software Interrupts
A software interrupt occurs when executing certain instructions. Software interrupts are non-maskable
interrupts.
9.1.1.1 Undefined Instruction Interrupt
An undefined instruction interrupt occurs when executing the UND instruction.
9.1.1.2 Overflow Interrupt
An overflow interrupt occurs when executing the INTO instruction with the O flag set to 1 (the opera-
tion resulted in an overflow). The following are instructions whose O flag changes by arithmetic: ABS,
ADC, ADCF, ADD, CMP, DIV, DIVU, DIVX, NEG, RMPA, SBB, SHA, SUB
9.1.1.3 BRK Interrupt
A BRK interrupt occurs when executing the BRK instruction.
9.1.1.4 INT Instruction Interrupt
An INT instruction interrupt occurs when executing the INT instruction. Software interrupt Nos. 0 to 63
can be specified for the INT instruction. Because software interrupt Nos. 1 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 Nos. 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 Nos. 32 to 63, the U flag does not
change state during instruction execution, and the SP then selected is used.
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