MC908QT4MPE datasheet(73/184 Pages) FREESCALE

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MC68HC908QY/QT Family Data Sheet, Rev. 5

Freescale Semiconductor

Chapter 8

External Interrupt (IRQ)

8.1 Introduction

The IRQ pin (external interrupt), shared with PTA2 (general purpose input) and keyboard interrupt (KBI),

provides a maskable interrupt input

8.2 Features

Features of the IRQ module include the following:

•

External interrupt pin, IRQ

•IRQ interrupt control bits

•

Programmable edge-only or edge and level interrupt sensitivity

•

Automatic interrupt acknowledge

•

Selectable internal pullup resistor

8.3 Functional Description

IRQ pin functionality is enabled by setting configuration register 2 (CONFIG2) IRQEN bit accordingly. A

zero disables the IRQ function and PTA2 will assume the other shared functionalities. A one enables the

IRQ function.

A low level applied to the external interrupt request (IRQ) pin can latch a CPU interrupt request.

Figure 8-2 shows the structure of the IRQ module.

Interrupt signals on the IRQ pin are latched into the IRQ latch. The IRQ latch remains set until one of the

following actions occurs:

•

IRQ vector fetch — An IRQ vector fetch automatically generates an interrupt acknowledge signal

that clears the IRQ latch.

•

Software clear — Software can clear the IRQ latch by writing a 1 to the ACK bit in the interrupt

status and control register (INTSCR).

•

Reset — A reset automatically clears the IRQ latch.

The external interrupt pin is falling-edge-triggered out of reset and is software-configurable to be either

falling-edge or falling-edge and low-level triggered. The MODE bit in INTSCR controls the triggering

sensitivity of the IRQ pin.

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