Mitsubishi microcomputers
M16C / 61 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Interrupt
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 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 assiging one of software interrupt numbers 0 through 63 and executing
the INT instruction. Software interrupt numbers 0 through 31 are assigned to peripheral I/O interrupts,
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 which software interrupt number is
involved.
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 re-
quest. So far as software numbers 32 through 63 are concerned, the stack pointer does not make a
shift.
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MITSUBISHI [ Mitsubishi Group ]
