Datasheet

Functional Description
MC68HC908GZ16 • MC68HC908GZ8 Data Sheet, Rev. 4
Freescale Semiconductor 105
Figure 9-2. Keyboard Module Block Diagram
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:
• 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 can also
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 $FFE0 and $FFE1.
• 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.
Addr.Register Name Bit 7654321Bit 0
$001A
Keyboard Status
and Control Register
(INTKBSCR)
See page 107.
Read:0000KEYF 0
IMASKK MODEK
Write:
ACKK
Reset:00000000
$001B
Keyboard Interrupt Enable
Register (INTKBIER)
See page 108.
Read:
KBIE7 KBIE6 KBIE5 KBIE4 KBIE3 KBIE2 KBIE1 KBIE0
Write:
Reset:00000000
= Unimplemented
Figure 9-3. I/O Register Summary
KB0IE
KB7IE
.
.
.
KEYBOARD
INTERRUPT
DQ
CK
CLR
V
DD
MODEK
IMASKK
REQUEST
VECTOR FETCH
DECODER
ACKK
INTERNAL BUS
RESET
TO PULLUP ENABLE
KBD7
KBD0
TO PULLUP ENABLE
SYNCHRONIZER
KEYF