NEC PD75402A - Manual (Page 151)

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CHAPTER 6. INTERRUPT FUNCTIONS
(4) Pending interrupt execution
Reset
EI
EI
EI
➀
IECSI
IE0
INT0
INTCSI
RETI
➁
RETI
➀ If INT0 and INTCSI are generated simultaneously (during execution of the same instruction), INT0, which
has the higher interrupt priority, is executed first (INTCSI is held pending).
➁ When the INT0 service program is ended by the RETI instruction, the pending INTCSI service program is
started.