NEC UPD789026 Series User Manual page 164

INTxx
During interrupt INTxx servicing, interrupt request INTyy is accepted, and a nesting is generated.
instruction is issued before each interrupt request acceptance, and the interrupt request acceptance enable state is
set.
Example 2. A nesting is not generated because interrupts are not enabled
Main Processing
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INTxx
Because interrupts are not enabled in interrupt INTxx servicing (an EI instruction is not issued), interrupt request
INTyy is not accepted, and a nesting is not generated. The INTyy request is reserved and accepted after the INTxx
processing is performed.
IE = 0: Interrupt request acceptance disabled
164
CHAPTER 10 INTERRUPT FUNCTIONS
Figure 10-14. Example of Nesting
Example 1. Nesting is accepted
Main Processing
IE = 0
EI
EI
IE = 0
User's Manual U11919EJ3V0UM00
INTxx Processing
IE = 0
EI
INTyy
RETI
INTxx Processing
INTyy
RETI
IE = 0
INTyy Processing
RETI
INTyy Processing
INTyy is kept pending
RETI
An EI