16C6KA datasheet(39/268 Pages) RENESAS

39 / 268 page

M16C/6KA Group

Rev.1.00

Jul 16, 2004

page 39 of 266

REJ03B0100-0100Z

Software Interrupts

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

rupts.

• 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 instructions whose O flag changes by arithmetic:

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 assigning one of software interrupt numbers 0 through 63 and executing the

INT instruction. Software interrupt numbers 0 through 52 are assigned to peripheral I/O interrupts, so ex-

ecuting 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 which software interrupt number is in-

volved.

So far as software interrupt numbers 0 through 31 are concerned, the microcomputer saves the stack pointer

assignment flag (U flag) when it accepts an interrupt request. If change the U flag to “0” and select the

interrupt stack pointer (ISP), and then execute an interrupt sequence. When returning from the interrupt

routine, the U flag is returned to the state it was before the acceptance of interrupt request. So far as

software numbers 32 through 63 are concerned, the stack pointer does not make a shift.

Interrupt

16C6KA Datasheet(PDF) 39 Page - Renesas Technology Corp