STM8S datasheet(60/467 Pages) STMICROELECTRONICS

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Interrupt controller (ITC)

RM0016

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DocID14587 Rev 14

Figure 13. Interrupt processing flowchart

Caution:

If the interrupt mask bits I0 and I1 are set within an interrupt service routine (ISR) with the

instruction SIM, removal of the interrupt mask with RIM causes the software priority to be

set to level 0.

To restore the correct priority when disabling and enabling interrupts inside an ISR, follow

the procedures presented in Table 8 for disabling and enabling the interrupts.

6.2.1

Servicing pending interrupts

Several interrupts can be pending at the same time. The interrupt to be taken into account is

determined by the following two-step process:

Table 8. Software priority levels

Software priority

Level

Level 0 (main)

Low

High

Level 1

Level 2

Level 3 (= software priority disabled)

MSv47744V1

RESET

PENDING

INTERRUPT

TRAP

TLI

I1:0

« IRET »

RESTORE PC, X, Y, A, CCR

FROM STACK

EXECUTE

INSTRUCTION

STACK PC, X, Y, A, CCR

LOAD I1:0 FROM INTERRUPT SW REG.

LOAD PC FROM INTERRUPT VECTOR

FETCH NEXT

INSTRUCTION

THE INTERRUPT

STAYS PENDING

Interrupt has the same or a

lower software priority

than current one

Table 9. Interrupt enabling/disabling inside an ISR

Disabling the interrupts

Enabling the interrupts

#asm

PUSH CC

POP ISR_CC(1)

SIM

#endasm

1. ISR_CC is a variable which stores the current value of the CC register.

#asm

PUSH ISR_CC(1)

POP CC

#endasm

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