MC908QT4MPE datasheet(79/184 Pages) FREESCALE

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MC68HC908QY/QT Family Data Sheet, Rev. 5

Freescale Semiconductor

Chapter 9

Keyboard Interrupt Module (KBI)

9.1 Introduction

The keyboard interrupt module (KBI) provides six independently maskable external interrupts, which are

accessible via the PTA0–PTA5 pins.

9.2 Features

Features of the keyboard interrupt module include:

•

Six keyboard interrupt pins with separate keyboard interrupt enable bits and one keyboard interrupt

mask

•

Software configurable pullup device if input pin is configured as input port bit

•

Programmable edge-only or edge and level interrupt sensitivity

•

Exit from low-power modes

9.3 Functional Description

The keyboard interrupt module controls the enabling/disabling of interrupt functions on the six port A pins.

These six pins can be enabled/disabled independently of each other. Refer to Figure 9-2.

9.3.1 Keyboard Operation

Writing to the KBIE0–KBIE5 bits in the keyboard interrupt enable register (KBIER) independently enables

or disables each port A pin as a keyboard interrupt pin. Enabling a keyboard interrupt pin in port A also

enables its internal pullup device irrespective of PTAPUEx bits in the port A input pullup enable register

(see 12.2.3 Port A Input Pullup Enable Register). A logic 0 applied to an enabled keyboard interrupt pin

latches a keyboard interrupt request.

A keyboard interrupt is latched when one or more keyboard interrupt inputs goes low after all were high.

The MODEK bit in the keyboard status and control register controls the triggering mode of the keyboard

interrupt.

•

If the keyboard interrupt is edge-sensitive only, a falling edge on a keyboard interrupt input does

not latch an interrupt request if another keyboard pin is already low. To prevent losing an interrupt

request on one input because another input is still low, software can disable the latter input while

it is low.

•

If the keyboard interrupt is falling edge and low-level sensitive, an interrupt request is present as

long as any keyboard interrupt input is low.

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