mc68hc908sr12 Freescale Semiconductor, Inc, mc68hc908sr12 Datasheet - Page 345

• Manufacturer Part Number: mc68hc908sr12
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

20.5 Functional Description
MC68HC908SR12•MC68HC08SR12 — Rev. 5.0
Freescale Semiconductor
KBI0
KBI7
TO PULLUP ENABLE
TO PULLUP ENABLE
KBIE0
KBIE7
.
.
.
Figure 20-2. Keyboard Interrupt Block Diagram
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 in 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 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:
•
•
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.
Keyboard Interrupt Module (KBI)
MODEK
V
DD
D
CK
CLR
Q
INTERRUPT FF
KEYBOARD
RESET
ACKK
VECTOR FETCH
Keyboard Interrupt Module (KBI)
INTERNAL BUS
DECODER
IMASKK
SYNCHRONIZER
Functional Description
KEYF
Data Sheet
Keyboard
Interrupt
Request
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