MC68HC908QL4 Datasheet, PDF (91/226 Pages) Motorola, Inc – Microcontrollers

Functional Description
The keyboard interrupt latch is set when one or more enabled keyboard interrupt inputs are asserted.
• If the keyboard interrupt sensitivity is edge-only, for KBIPx = 0, a falling (for KBIPx = 1, a rising)
edge on a keyboard interrupt input does not latch an interrupt request if another enabled keyboard
pin is already asserted. To prevent losing an interrupt request on one input because another input
remains asserted, software can disable the latter input while it is asserted.
• If the keyboard interrupt is edge and level sensitive, an interrupt request is present as long as any
enabled keyboard interrupt input is asserted.
INTERNAL BUS
KBI0
KBIP0
VECTOR FETCH
DECODER
ACKK
RESET
1
0S
KBIE0
TO PULLUP/
PULLDOWN ENABLE
(see Note)
1
KBIx
0S
KBIPx
AWUIREQ
(SEE Figure 4-1)
KBIEx
TO PULLUP/
PULLDOWN ENABLE
(see Note)
V_DD
CLR
D
Q
CK
KBI LATCH
MODEK
KEYF
SYNCHRONIZER
IMASKK
KEYBOARD
INTERRUPT
REQUEST
NOTE:
To enable internal pullup/pulldown, requires both the KBIPx and the corresponding PTAPUEN to both be set.
Figure 9-2. Keyboard Interrupt Block Diagram
9.3.1.1 MODEK = 1
If the MODEK bit is set, the keyboard interrupt inputs are both edge and level sensitive. The KBIPx bit will
determine whether a edge sensitive pin detects rising or falling edges and on level sensitive pins whether
the pin detects low or high levels. With MODEK set, both of the following actions must occur to clear a
keyboard interrupt request:
• Return of all enabled keyboard interrupt inputs to a deasserted level. As long as any enabled
keyboard interrupt pin is asserted, the keyboard interrupt remains active.
• 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
MC68HC908QL4 Data Sheet, Rev. 7
Freescale Semiconductor
91