mc68hc908qf4 Freescale Semiconductor, Inc, mc68hc908qf4 Datasheet - Page 82

• Manufacturer Part Number: mc68hc908qf4
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Keyboard Interrupt Module (KBI)
Data Sheet
82
NOTE:
If the MODEK bit is set, the keyboard interrupt inputs are both falling edge and
low-level sensitive, and both of the following actions must occur to clear a keyboard
interrupt request:
The vector fetch or software clear and the return of all enabled keyboard interrupt
pins to logic 1 may occur in any order.
If the MODEK bit is clear, the keyboard interrupt pin is falling-edge sensitive only.
With MODEK clear, a vector fetch or software clear immediately clears the
keyboard interrupt request.
Reset clears the keyboard interrupt request and the MODEK bit, clearing the
interrupt request even if a keyboard interrupt input stays at logic 0.
The keyboard flag bit (KEYF) in the keyboard status and control register can be
used to see if a pending interrupt exists. The KEYF bit is not affected by the
keyboard interrupt mask bit (IMASKK) which makes it useful in applications where
polling is preferred.
To determine the logic level on a keyboard interrupt pin, use the data direction
register to configure the pin as an input and then read the data register.
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.
•
•
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 (KBSCR). The ACKK bit is useful in
applications that poll the keyboard interrupt inputs 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 inputs. 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 central processor unit (CPU) loads the program
counter with the vector address at locations $FFE0 and $FFE1.
Return of all enabled keyboard interrupt inputs to logic 1 — As long as any
enabled keyboard interrupt pin is at logic 0, the keyboard interrupt remains
set. The auto wakeup interrupt input, AWUIREQ, will be cleared only by
writing to ACKK bit in KBSCR or reset.
Freescale Semiconductor, Inc.
For More Information On This Product,
Keyboard Interrupt Module (KBI)
Go to: www.freescale.com
MC68HC908QF4 — Rev. 1.0
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