mc68hc908ey16a Freescale Semiconductor, Inc, mc68hc908ey16a Datasheet - Page 115

• Manufacturer Part Number: mc68hc908ey16a
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

10.3.1.1 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:
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.
10.3.1.2 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.
Freescale Semiconductor
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•
KBD0
KBDx
KBIP0
KBIPx
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 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.
1
0
1
0
VECTOR FETCH
S
S
INTERNAL BUS
DECODER
TO PULLUP/
PULLDOWN ENABLE
TO PULLUP/
PULLDOWN ENABLE
KBIE0
KBIEx
Figure 10-2. Keyboard Interrupt Block Diagram
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 1
RESET
ACKK
MODEK
V
DD
D
KBI LATCH
CK
CLR
Q
IMASKK
SYNCHRONIZER
Functional Description
KEYF
KEYBOARD
INTERRUPT
REQUEST
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