NEC switch - Manual (Page 176)

CHAPTER 11 INTERRUPT FUNCTIONS
User’s Manual U12978EJ3V0UD
176
Figure 11-14. Example of Multiplexed Interrupt Servicing
Example 1. Acknowledging multiplexed interrupts
INTyy
EI
Main processing
EI
INTyy processing INTxx processing
RETI
IE = 0
INTxx
RETI
IE = 0
The interrupt request INTyy is acknowledged and multiplexed interrupt servicing is performed during the interrupt
INTxx servicing. Before each interrupt is acknowledged, the IE instruction is issued and interrupt requests are
enabled.
Example 2. Multiplexed interrupts are not performed because interrupts are disabled.
INTyy
EI
Main processing
RETI
INTyy processing INTxx processing
IE = 0
INTxx
RETI
INTyy is held pending
IE = 0
Interrupt requests are disabled (EI instruction is not issued) in the interrupt INTxx servicing. The interrupt request
INTyy is not acknowledged and multiplexed interrupt servicing is not performed. INTyy is held pending and is
acknowledged after INTxx servicing is completed.
IE = 0: Interrupt request acknowledgment disabled.