MC68HC908JK3 MOTOROLA [Motorola, Inc], MC68HC908JK3 Datasheet - Page 167

• Manufacturer Part Number: MC68HC908JK3
• Description: MC68HC908JK1
• Manufacturer: MOTOROLA [Motorola, Inc]

MC68H(R)C908JL3
MOTOROLA
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Rev. 1.0
A keyboard interrupt is latched when one or more keyboard pins 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 pins 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.
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If the keyboard interrupt is edge-sensitive only, a falling edge on a
keyboard pin does not latch an interrupt request if another
keyboard pin is already low. To prevent losing an interrupt request
on one pin because another pin is still low, software can disable
the latter pin 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 pin 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 pins 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 pins. 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 CPU loads the
program counter with the vector address at locations $FFE0 and
$FFE1.
Return of all enabled keyboard interrupt pins to logic 1 — As long
as any enabled keyboard interrupt pin is at logic 0, the keyboard
interrupt remains set.
Keyboard Interrupt Module (KBI)
Keyboard Interrupt Module (KBI)
Functional Description
Technical Data
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