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CHAPTER 21 INTERRUPT AND TEST FUNCTIONS
Figure 21-13. Interrupt Request Acknowledge Processing Algorithm××IF : Interrupt request flag××MK : Interrupt mask flag××PR : Priority specify flagIE : Flag to control acknowledgment of maskable interrupt request (1 = enable, 0 = disable)ISP : Flag to indicate the priority of interrupt currently being serviced (0 = servicing interrupt of high priority,1 = not acknowledging interrupt request or servicing interrupt of low priority)

Start

× × IF=1?

× × MK=0?

× × PR=0?

Any
Simultaneously
generated ××PR=0
interrupt requests?
Any
Simultaneously
generated high-priority
interrupt requests?

IE=1?

ISP=1?

Vectored interrupt
servicing
Interrupt request
reserve
Interrupt request
reserve
Interrupt request
reserve
Interrupt request
reserve
Interrupt request
reserve
Interrupt request
reserve
Interrupt request
reserve Vectored interrupt
servicing
Any high-
priority interrupt request
among simultaneously generated
××PR=0 interrupt
requests?

IE=1?

Yes (High priority)
Yes
No
Yes
No
No
No
Yes (Interrupt Request
Generation)
No
Yes
No (Low Priority)
Yes
Yes
No
Yes
Yes
No
No