UPD70F3208 Datasheet, PDF (650/757 Pages) NEC – 32-Bit Single-Chip Microcontrollers

CHAPTER 19 INTERRUPT/EXCEPTION PROCESSING FUNCTION
19.6 Multiple Interrupt Servicing Control
Multiple interrupt servicing control is a function that stops an interrupt service routine currently in progress if a
higher priority interrupt request is generated, and processes the acknowledgement operation of the higher priority
interrupt.
If an interrupt with a lower or equal priority is generated and a service routine is currently in progress, the later
interrupt will be held pending.
Multiple interrupt servicing control is performed when interrupts are enabled (ID = 0). Even in an interrupt servicing
routine, multiple interrupt control must be performed while interrupts are enabled (ID = 0). If a maskable interrupt or
software exception is generated in a maskable interrupt or software exception service program, EIPC and EIPSW
must be saved.
The following example illustrates the procedure.
(1) To acknowledge maskable interrupt requests in service program
Service program for maskable interrupt or exception
…
…
• EIPC saved to memory or register
• EIPSW saved to memory or register
• EI instruction (enables interrupt acknowledgement)
…
…
…
…
• DI instruction (disables interrupt acknowledgement)
• Saved value restored to EIPSW
• Saved value restored to EIPC
• RETI instruction
←Acknowledges maskable interrupt
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User’s Manual U15862EJ3V0UD