Nintendo DMG-01 Manual - Page 33

Interrupt Procedure

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Game BoyTM CPU Manual 2.12.1. Interrupt Procedure Resetting of the IF register, which was the cause of the interrupt, is done by hardware. During the interrupt, pushing of registers to be used should be performed by the interrupt routine. Once the interrupt service is in progress, all the interrupts will be prohibited. However, if the IME flag and the IE flag are controlled, a number of interrupt services can be made possible by nesting. Return from an interrupt routine can be performed by either RETI or RET instruction. The RETI instruction enables interrupts after doing a return operation. If a RET is used as the final instruction in an interrupt routine, interrupts will remain disabled unless a EI was used in the interrupt routine or is used at a later time. The interrupt will be acknowledged during opcode fetch period of each instruction. by DP Page 33

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Game Boy
TM
CPU Manual
2.12.1. Interrupt Procedure
Resetting of the IF register, which was the cause of
the interrupt, is done by hardware.
During the interrupt, pushing of registers to be used
should be performed by the interrupt routine.
Once the interrupt service is in progress, all the
interrupts will be prohibited. However, if the IME
flag and the IE flag are controlled, a number of
interrupt services can be made possible by nesting.
Return from an interrupt routine can be performed by
either RETI or RET instruction.
The RETI instruction enables interrupts after doing a
return operation.
If a RET is used as the final instruction in an
interrupt routine, interrupts will remain disabled
unless a EI was used in the interrupt routine or is
used at a later time.
The interrupt will be
acknowledged during opcode fetch period of each
instruction.
by DP
Page 33