495CHAPTER 21 INTERRUPT AND TEST FUNCTIONSFigure 21-13. Interrupt Request Acknowledge Processing AlgorithmXXIF : Interrupt Request FlagXXMK : Interrupt Mask FlagXXPR : Priority Order Specification FlagIE : Flag which controls reception of maskable interrupt requests (1 = permitted, 0 = prohibited)ISP : Flag which shows the priority order of the interrupt currently being processed (0 = high priority orderinterrupt being processed, 1 = no interrupt request being received, or low priority order interrupt beingprocessed.)Start× × IF=1?× × MK=0?× × PR=0?AnySimultaneouslygenerated ××PR=0interrupt requests?AnySimultaneouslygenerated high-priorityinterrupt requests?IE=1?ISP=1?Vectored interruptservicingInterrupt requestreserveInterrupt requestreserveInterrupt requestreserveInterrupt requestreserveInterrupt requestreserveInterrupt requestreserveInterrupt requestreserve Vectored interruptservicingDoes one ofthe simultaneously generatedXXPR=0 interrupt request have ahigh priority?IE=1?Yes (High priority)YesNoYesNoNoNoYes (Interrupt RequestGeneration)NoYesNo (Low Priority)YesYesNoYesYesNoNo
