MC68HC908QY4CDW Datasheet, PDF (81/184 Pages) Freescale Semiconductor, Inc – Microcontrollers

Functional Description
INTERNAL BUS
KBI0
.
KBIE0
.
TO PULLUP ENABLE
.
KBI5
V_DD
D ^CLR Q
CK
ACKK
RESET
VECTOR FETCH
DECODER
KEYF
SYNCHRONIZER
KEYBOARD
INTERRUPT FF
IMASKK
KEYBOARD
INTERRUPT
REQUEST
KBIE5
TO PULLUP ENABLE
MODEK
AWUIREQ⁽¹⁾
1. For AWUGEN logic refer to Figure 4-1. Auto Wakeup Interrupt Request Generation Logic.
Figure 9-2. Keyboard Interrupt Block Diagram
If the MODEK bit is set, the keyboard interrupt inputs 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 may generate the interrupt acknowledge signal by writing a 1 to the
ACKK bit in the keyboard status and control register (KBSCR). The ACKK bit is useful in
applications that poll the keyboard interrupt inputs and require software to clear the keyboard
interrupt request. Writing to the ACKK bit prior to leaving an interrupt service routine can also
prevent spurious interrupts due to noise. Setting ACKK does not affect subsequent transitions on
the keyboard interrupt inputs. 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 central
processor unit (CPU) loads the program counter with the vector address at locations $FFE0 and
$FFE1.
• Return of all enabled keyboard interrupt inputs to logic 1 — As long as any enabled keyboard
interrupt pin is at logic 0, the keyboard interrupt remains set. The auto wakeup interrupt input,
AWUIREQ, will be cleared only by writing to ACKK bit in KBSCR or reset.
The vector fetch or software clear and the return of all enabled keyboard interrupt pins to logic 1 may occur
in any order.
If the MODEK bit is clear, the keyboard interrupt pin is falling-edge sensitive only. With MODEK clear, a
vector fetch or software clear immediately clears the keyboard interrupt request.
Reset clears the keyboard interrupt request and the MODEK bit, clearing the interrupt request even if a
keyboard interrupt input stays at logic 0.
The keyboard flag bit (KEYF) in the keyboard status and control register can be used to see if a pending
interrupt exists. The KEYF bit is not affected by the keyboard interrupt mask bit (IMASKK) which makes
it useful in applications where polling is preferred.
MC68HC908QY/QT Family Data Sheet, Rev. 6
Freescale Semiconductor
81