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CHAPTER 3 INTERRUPTS
3.4
Interrupt Flow
Figure 3.4-1 shows the interrupt flow.
■ Interrupt Flow
Fetching and decoding
the next instruction
Executing an ordinary
NO
string instruction
62
Figure 3.4-1 Interrupt Flow
YES
I & IF & IE = 1
AND
ILM > IL
NO
stack of SSP, and setting ILM=IL
YES
INT instruction
NO
instruction
Completion of
repetition
YES
Updating PC
I: Flag in CCR
ILM: Level register in CPU
IF: Internal resource interrupt request
IE: Internal resource interrupt enable flag
2
ISE: EI
OS enable flag
IL: Internal resource interrupt request level
S: Flag in CCR
NO
Saving PS, PC, PCB, DTB,
ADB, DPR, and A into the
Saving PS, PC, PCB, DTB, ADB,
DPR, and A into the stack of SSP,
and setting I=0 and ILM=IL
S← 1
Fetching the interrupt vector
YES
ISE = 1
Executing the extended
intelligent I/O service
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