MC68HC908LJ12 Datasheet, PDF (364/413 Pages) Freescale Semiconductor, Inc – 8-bit microcontroller units

Keyboard Interrupt Module (KBI)
19.5 Functional Description
INTERNAL BUS
KBI0
.
KBIE0
.
TO PULLUP ENABLE
.
KBI7
KBIE7
TO PULLUP ENABLE
V_DD
D ^CLR Q
CK
ACKK
RESET
KEYBOARD
INTERRUPT FF
VECTOR FETCH
DECODER
KEYF
SYNCHRONIZER
KEYBOARD
INTERRUPT
REQUEST
IMASKK
MODEK
Figure 19-2. Keyboard Interrupt Block Diagram
Writing to the KBIE7–KBIE0 bits in the keyboard interrupt enable register
independently enables or disables a port A or port D pin as a keyboard
interrupt pin. Enabling a keyboard interrupt pin in port A or port D also
enables its internal pull-up 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 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:
MC68HC908LJ12 — Rev. 2.1
Freescale Semiconductor
Keyboard Interrupt Module (KBI)
Technical Data
365