MC68HC08XL36 Datasheet, PDF (311/362 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Keyboard Interrupt Module (KBI)
Functional Description
Functional Description
Writing to the KBIE7–KBIE0 bits in the keyboard interrupt enable register
independently enables or disables each port D 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 request 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 sensitivity of the keyboard
interrupt pins.
• If the keyboard interrupt pins are 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 pins are falling edge- and low
level-sensitive, an interrupt request is present as long as any
keyboard pin is low.
If the MODEK bit is set, the keyboard interrupt pins are both falling edge-
and low level-sensitive, and both of the following actions must occur to
clear a keyboard interrupt request:
• Vector fetch or software clear — A vector fetch generates an
interrupt acknowledge signal to clear the interrupt request.
Software can generate the interrupt acknowledge signal by writing
a logic 1 to the ACKK bit in the keyboard status and control
register. The ACKK bit is useful in applications that poll the
keyboard interrupt pins and require software to clear the keyboard
interrupt request. Writing to the ACKK bit in an interrupt service
routine can also prevent spurious interrupts due to noise. Setting
ACKK does not affect subsequent transitions on the keyboard
interrupt pins. A falling edge that occurs after writing to the ACKK
bit latches another interrupt request. If the keyboard interrupt
mask bit, IMASKK, is clear, the CPU loads the program counter
with the vector address at locations $FFDE and $FFDF.
3-intkbd8_a
MOTOROLA
Keyboard Interrupt Module (KBI)
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MC68HC08XL36
311