ST72321BR9-AUTO View Datasheet(PDF) - STMicroelectronics

Part Name

Description

MFG CO.

ST72321BR9-AUTO

8-bit MCU for automotive with 32 to 60 Kbyte Flash/ROM, ADC, 5 timers, SPI, SCI, I2C interface

STMicroelectronics 

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Interrupts

ST72321Bxxx-Auto

Table 14. Interrupt software priority levels

Interrupt software priority

Level

I1

I0

Level 0 (main)

Level 1

Level 2

Level 3 (= interrupt disable)

Low

1

0

0

1

0

0

High

1

1

Figure 17. Interrupt processing flowchart

RESET

RESTORE PC, X, A, CC

FROM STACK

PENDING

Y

INTERRUPT

N

TRAP Y

Interrupt has the same or a

lower software priority

than current one

N

I1:0

FETCH NEXT

INSTRUCTION

THE INTERRUPT

STAYS PENDING

Y “IRET”

N

EXECUTE

INSTRUCTION

STACK PC, X, A, CC

LOAD I1:0 FROM INTERRUPT SW REG.

LOAD PC FROM INTERRUPT VECTOR

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 18 describes this decision process.

Figure 18. Priority decision process flowchart

PENDING

INTERRUPTS

Same

SOFTWARE

PRIORITY

Different

HIGHEST SOFTWARE

PRIORITY SERVICED

HIGHEST HARDWARE

PRIORITY SERVICED

56/247

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