Datasheet

Keyboard Interrupt Module (KBI)
MC68HC908AB32 — Rev. 1.1 Technical Data
Freescale Semiconductor Keyboard Interrupt Module (KBI)
347
19.5 Functional Description
Figure 19-2. Keyboard Interrupt Block Diagram
Writing to the KBIE4–KBIE0 bits in the keyboard interrupt enable register
independently enables or disables the corresponding port pin as a
keyboard interrupt pin. Enabling a keyboard interrupt pin 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:
KBIE0
KBIE4
.
.
.
DQ
CK
CLR
V
DD
MODEK
IMASKK
KEYBOARD
INTERRUPT FF
VECTOR FETCH
DECODER
ACKK
INTERNAL BUS
RESET
KBD4
KBD0
SYNCHRONIZER
KEYF
Keyboard
Interrupt
Request
TO PULLUP ENABLE
TO PULLUP ENABLE