NEC mPD789101 User Manual page 216

Main processing
EI
INTxx
During interrupt INTxx servicing, interrupt request INTyy is acknowledged, and a multiple interrupt is generated.
An EI instruction is issued before each interrupt request acknowledgement, and the interrupt request acknowledgement
enable state is set.
Example 2. A multiple interrupt is not generated because interrupts are not enabled
Main processing
EI
INTxx
Because interrupts are not enabled in interrupt INTxx servicing (an EI instruction is not issued), interrupt request
INTyy is not acknowledged, and a multiple interrupt is not generated. The INTyy request is reserved and acknowledged
after the INTxx processing is performed.
IE = 0: Interrupt request acknowledgement disabled
216
CHAPTER 15 INTERRUPT FUNCTIONS
Figure 15-12. Example of Multiple Interrupts
Example 1. Multiple interrupts are acknowledged
INTxx processing
IE = 0
INTyy
INTxx processing
IE = 0
INTyy
RETI
IE = 0
User's Manual U13045EJ2V0UM00
IE = 0
EI
RETI
INTyy is kept pending
INTyy processing
RETI
INTyy processing
RETI