238
CHAPTER 19 INTERRUPT FUNCTIONS
Figure 19-11. Interrupt Request Acknowledge Processing Algorithm
Start
××
IF = 1?
××
MK = 0?
××
PR = 0?
IE = 1?
ISP = 1?
Interrupt request held pending
Yes
Yes
No
No
Yes (Interrupt request generation)
Yes
No (Low priority)
No
No
Yes
Yes
No
IE = 1?
No
Any high-priority
interrupt request among those
simultaneously generated
with
××
PR = 0?
Yes (High priority)
No
Yes
Yes
No
Vectored interrupt servicing
Interrupt request held pending
Interrupt request held pending
Interrupt request held pending
Interrupt request held pending
Interrupt request held pending
Interrupt request held pending
Vectored interrupt servicing
Any interrupt
request among
those simultaneously
generated?
Any interrupt
request among those
simultaneously generated
with
××
PR = 0?
××
IF
: Interrupt request flag
××
MK : Interrupt mask flag
××
PR : Priority specify flag
IE
: Flag that controls acknowledge of maskable interrupt request (1 = Enable, 0 = Disable)
ISP
: Flag that indicates the priority level of the interrupt currently being serviced (0 = High-priority interrupt
servicing, 1 = No interrupt request acknowledged, or low-priority interrupt servicing)
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