MC68HC908GT16_07 Datasheet, PDF (109/292 Pages) Freescale Semiconductor, Inc – Microcontrollers

Functional Description
INTERNAL BUS
KBD0
TO PULLUP ENABLE
.
.
KB0IE
.
KBD7
V_DD
RESET
CLR
D
Q
CK
ACKK
VECTOR FETCH
DECODER
KEYF
SYNCHRONIZER
IMASKK
KEYBOARD
INTERRUPT
REQUEST
TO PULLUP ENABLE
KB7IE
MODEK
Figure 9-2. Keyboard Module Block Diagram
Addr.
$001A
$001B
Register Name
Keyboard Status
and Control Register
(INTKBSCR)
See page 111.
Read:
Write:
Reset:
Keyboard Interrupt Enable
Register
(INTKBIER)
See page 112.
Read:
Write:
Reset:
Bit 7
0
0
KBIE7
0
6
5
0
0
0
0
KBIE6 KBIE5
0
0
= Unimplemented
4
0
0
KBIE4
0
3
KEYF
0
KBIE3
0
Figure 9-3. I/O Register Summary
2
0
ACKK
0
KBIE2
0
1
Bit 0
IMASKK MODEK
0
0
KBIE1 KBIE0
0
0
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 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.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
109