M68HC08 datasheet(97/188 Pages) FREESCALE

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Keyboard/External Interrupt Module (KBI)

Functional Description

MC68HC908RF2 — Rev. 4.0

Data Sheet

MOTOROLA

Keyboard/External Interrupt Module (KBI)

Figure 7-4. IRQ Interrupt Flowchart

If the MODEI bit is clear, the IRQ pin is falling-edge sensitive only. With MODEI

clear, a vector fetch or software clear immediately clears the IRQ1 latch.The IRQ1F

bit in the INTKBSCR register can be used to check for pending interrupts. The

IRQ1F bit is not affected by the IMASKI bit, which makes it useful in applications

where polling is preferred.

Use the BIH or BIL instruction to read the logic level on the IRQ pin.

NOTE:

When using the level-sensitive interrupt trigger, avoid false interrupts by masking

interrupt requests in the interrupt routine.

FROM RESET

I BIT SET?

FETCH NEXT

YES

INTERRUPT?

INSTRUCTION

SWI

INSTRUCTION?

RTI

INSTRUCTION?

STACK CPU REGISTERS

SET I BIT

LOAD PC WITH INTERRUPT VECTOR

YES

UNSTACK CPU REGISTERS

EXECUTE INSTRUCTION

YES

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