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Interrupts

Renesas Technology Corp.

M16C/26 Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Under

development

Preliminary Specifications Rev. 0.9

Specifications in this manual are tentative and subject to change.

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 overflow flag (O flag) set to

“1”. The following are arithmetic instructions changes O flag:

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 interrupt

An INT interrupt occurs when specifying one of software interrupt numbers 0 through 63 and execut-

ing the INT instruction. Software interrupt numbers 0 through 31 are assigned to peripheral I/O inter-

rupts, so executing the INT instruction allows executing the same interrupt routine that a peripheral I/

O interrupt does.

The stack pointer (SP) used for the INT interrupt is dependent on the software interrupt number

involved.

For software interrupt numbers 0 through 31, the microcomputer saves the stack pointer assignment

flag (U flag) when it accepts an interrupt request. The U flag is changed to “0” and the interrupt stack

pointer (ISP) is selected, and then, the interrupt sequence is executed. When returning from the

interrupt routine, the U flag is returned to the state it was before the interrupt request was accepted.

For software numbers 32 through 63, the U flag is not changed, and so the stack pointer is not

affected.

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