NEC 78K0 User Manual page 327

Example 1. Multiple interrupt servicing occurs twice
Main processing
INTxx
(PR = 1)
During servicing of interrupt INTxx, two interrupt requests, INTyy and INTzz, are acknowledged, and multiple
interrupt servicing takes place. Before each interrupt request is acknowledged, the EI instruction must always be
issued to enable interrupt request acknowledgment.
Example 2. Multiple interrupt servicing does not occur due to priority control
Interrupt request INTyy issued during servicing of interrupt INTxx is not acknowledged because its priority is lower
than that of INTxx, and multiple interrupt servicing does not take place. The INTyy interrupt request is held pending,
and is acknowledged following execution of one main processing instruction.
PR = 0: Higher priority level
PR = 1: Lower priority level
IE = 0: Interrupt request acknowledgment disabled
CHAPTER 15 INTERRUPT FUNCTIONS
Figure 15-10. Examples of Multiple Interrupt Servicing (1/2)
INTxx servicing
IE = 0
EI
EI
INTyy
(PR = 0)
IE = 1 RETI
Main processing
EI IE = 0
INTxx INTyy
(PR = 0) (PR = 1)
IE = 1
1 instruction execution
User's Manual U16227EJ2V0UD
INTyy servicing
IE = 0 IE = 0
EI
INTzz
(PR = 0)
IE = 1
IE = 1 RETI
INTxx servicing INTyy servicing
EI
RETI
IE = 0
RETI
IE = 1
INTzz servicing
RETI
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