mc68hc908rk2 Freescale Semiconductor, Inc, mc68hc908rk2 Datasheet - Page 188

• Manufacturer Part Number: mc68hc908rk2
• Description: Hcmos Microcontroller Unit
• Manufacturer: Freescale Semiconductor, Inc

Keyboard/External Interrupt Module (KBI)
Advance Information
188
TO PULLUP
TO PULLUP
KBD1
KBD6
ENABLE
ENABLE
KB1IE
KB6IE
.
.
.
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.
Keyboard/External Interrupt Module (KBI)
MODEK
V
DD
D
CK
CLR
INTERRUPT LATCH
Q
KEYBOARD
RESET
ACKK
IMASKK
VECTOR FETCH
SYNCHRONIZER
DECODER
MC68HC908RK2
INTERRUPT
INTERNAL BUS
REQUEST
KEYF
IRQ1
KEYBOARD
INTERRUPT
REQUEST
IRQ1/KEYBOARD
INTERRUPT
REQUEST
MOTOROLA
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Rev. 4.0