Datasheet

Keyboard Interrupt (KBI)

Technical Data MC68HC908GR8 — Rev 4.0

176 Keyboard Interrupt (KBI) MOTOROLA

13.4 Functional Description

Writing to the KBIE3–KBIE0 bits in the keyboard interrupt enable register

independently enables or disables each port A pin as a keyboard

interrupt pin. Enabling a keyboard interrupt pin also enables its internal

pullup device. 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 pins 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 pin does not latch an interrupt request if another

keyboard pin is already low. To prevent losing an interrupt request

on one pin because another pin is still low, software can disable

the latter pin 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 pin

is low and the pin is keyboard interrupt enabled.

Frees

cale Semiconductor,

Freescale Semiconductor, Inc.

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