mc68hc908qb4 Freescale Semiconductor, Inc, mc68hc908qb4 Datasheet - Page 85

• Manufacturer Part Number: mc68hc908qb4
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

The KBI vector fetch or software clear and the return of all enabled keyboard interrupt pins to a deasserted
level may occur in any order.
Reset clears the keyboard interrupt request and the MODEK bit, clearing the interrupt request even if a
keyboard interrupt input stays asserted.
9.3.1.2 MODEK = 0
If the MODEK bit is clear, the keyboard interrupt inputs are edge sensitive. The KBIPx bit will determine
whether an edge sensitive pin detects rising or falling edges. A KBI vector fetch or software clear
immediately clears the KBI latch.
The keyboard flag bit (KEYF) in KBSCR can be read to check for pending interrupts. The KEYF bit is not
affected by IMASKK, which makes it useful in applications where polling is preferred.
Freescale Semiconductor
•
KBI0
KBIx
KBIP0
KBIPx
(SEE
Vector fetch or software clear. A KBI vector fetch generates an interrupt acknowledge signal to
clear the KBI latch. Software generates the interrupt acknowledge signal by writing a 1 to ACKK in
KBSCR. The ACKK bit is useful in applications that poll the keyboard interrupt inputs and require
software to clear the KBI latch. Writing to ACKK 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. An edge detect that occurs after writing to ACKK latches another
interrupt request. If the keyboard interrupt mask bit, IMASKK, is clear, the CPU loads the program
counter with the KBI vector address.
AWUIREQ
Figure
4-1)
1
0
1
0
VECTOR FETCH
S
S
INTERNAL BUS
Setting a keyboard interrupt enable bit (KBIEx) forces the corresponding
keyboard interrupt pin to be an input, overriding the data direction register.
However, the data direction register bit must be a 0 for software to read the
pin.
DECODER
TO PULLUP/
PULLDOWN ENABLE
TO PULLUP/
PULLDOWN ENABLE
KBIE0
KBIEx
Figure 9-2. Keyboard Interrupt Block Diagram
RESET
ACKK
MC68HC908QB8 Data Sheet, Rev. 2
MODEK
NOTE
V
DD
D
KBI LATCH
CK
CLR
Q
IMASKK
SYNCHRONIZER
Functional Description
KEYF
KEYBOARD
INTERRUPT
REQUEST
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