NEC mPD78F0730 Preliminary User's Manual page 406

Example 1. Multiple interrupt servicing occurs twice
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
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CHAPTER 13 INTERRUPT FUNCTIONS
Figure 13-10. Examples of Multiple Interrupt Servicing (1/2)
Main processing INTxx servicing
IE = 0
EI
INTxx INTyy
(PR = 1) (PR = 0)
IE = 1
Main processing
EI
INTxx
(PR = 0)
1 instruction execution
Preliminary User's Manual U19014EJ1V0UD
INTyy servicing
IE = 0
EI
EI
INTzz
(PR = 0)
RETI IE = 1 RETI
INTxx servicing INTyy servicing
IE = 0
EI
INTyy
(PR = 1)
RETI
IE = 1
IE = 0
IE = 1
INTzz servicing
IE = 0
RETI
IE = 1
RETI