ST72344S2 datasheet(54/247 Pages) STMICROELECTRONICS

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Interrupts

ST72344xx, ST2345xx

54/247

Doc ID 12321 Rev 6

Figure 20.

Interrupt processing flowchart

Servicing pending interrupts

As several interrupts can be pending at the same time, the interrupt to be taken into account

is determined by the following two-step process:

●

the highest software priority interrupt is serviced,

●

if several interrupts have the same software priority, then the interrupt with the highest

hardware priority is serviced first.

Figure 21 describes this decision process.

Figure 21.

Priority decision process

Table 13.

Interrupt software priority levels

Interrupt software priority

Level

Level 0 (main)

Low

High

Level 1

Level 2

Level 3 (= interrupt disable)

“IRET”

RESTORE PC, X, A, CC

STACK PC, X, A, CC

LOAD I1:0 FROM INTERRUPT SW REG.

FETCH NEXT

RESET

TRAP

PENDING

INSTRUCTION

I1:0

FROM STACK

LOAD PC FROM INTERRUPT VECTOR

Interrupt has the same or a

lower software priority

THE INTERRUPT

STAYS PENDING

than current one

EXECUTE

INSTRUCTION

INTERRUPT

PENDING

SOFTWARE

Different

INTERRUPTS

Same

HIGHEST HARDWARE

PRIORITY SERVICED

PRIORITY

HIGHEST SOFTWARE

PRIORITY SERVICED

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