MC68HC908QY2 MOTOROLA [Motorola, Inc], MC68HC908QY2 Datasheet - Page 180

• Manufacturer Part Number: MC68HC908QY2
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Keyboard Interrupt Module (KBI)
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A keyboard interrupt is latched when one or more keyboard interrupt
inputs goes low after all were high. The MODEK bit in the keyboard
status and control register controls the triggering mode of the keyboard
interrupt.
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:
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If the keyboard interrupt is edge-sensitive only, a falling edge on a
keyboard interrupt input does not latch an interrupt request if
another keyboard pin is already low. To prevent losing an interrupt
request on one input because another input is still low, software
can disable the latter input while it is low.
If the keyboard interrupt is falling edge and low-level sensitive, an
interrupt request is present as long as any keyboard interrupt input
is low.
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 logic 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 wake-up interrupt input,
AWUIREQ, will be cleared only by writing to ACKK bit in KBSCR
or reset.
Keyboard Interrupt Module (KBI)
MOTOROLA