MC68HC908RK2 Datasheet, PDF (188/232 Pages) Motorola, Inc – Microcontroller Unit

Keyboard/External Interrupt Module (KBI)
KBD1
TO PULLUP
ENABLE
KB1IE
KBD6
TO PULLUP
ENABLE
KB6IE
INTERNAL BUS
VECTOR FETCH
ACKK
DECODER
V_DD
RESET
KEYF
.
CLR
D
Q
.
CK
SYNCHRONIZER
KEYBOARD
.
INTERRUPT
REQUEST
KEYBOARD
INTERRUPT LATCH
IMASKK
MODEK
IRQ1
INTERRUPT
REQUEST
IRQ1/KEYBOARD
INTERRUPT
REQUEST
Figure 14-4. Keyboard Interrupt Block Diagram
If the MODEK bit is set, the keyboard interrupt pins are both falling edge-
and low level-sensitive, and both of these 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 logic 1 to the ACKK bit in the keyboard status and control
register (INTKBSCR). 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 prior to leaving
an interrupt service routine also can 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 $FFFA and
$FFFB.
• Return of all enabled keyboard interrupt pins to logic 1. As long as
any enabled keyboard interrupt pin is at logic 0, the keyboard
interrupt remains set.
Advance Information
188
Keyboard/External Interrupt Module (KBI)
MC68HC908RK2 — Rev. 4.0
MOTOROLA