MC68HC908LK24 MOTOROLA [Motorola, Inc], MC68HC908LK24 Datasheet - Page 411

• Manufacturer Part Number: MC68HC908LK24
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

20.5.1 Keyboard Initialization
MC68HC908LJ24/LK24 — Rev. 2
MOTOROLA
NOTE:
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 logic 0 for
software to read the pin.
When a keyboard interrupt pin is enabled, it takes time for the internal
pullup to reach a logic 1. Therefore a false interrupt can occur as soon
as the pin is enabled.
To prevent a false interrupt on keyboard initialization:
An interrupt signal on an edge-triggered pin can be acknowledged
immediately after enabling the pin. An interrupt signal on an edge- and
level-triggered interrupt pin must be acknowledged after a delay that
depends on the external load.
Another way to avoid a false interrupt:
1. Mask keyboard interrupts by setting the IMASKK bit in the
2. Enable the KBI pins by setting the appropriate KBIEx bits in the
3. Write to the ACKK bit in the keyboard status and control register
4. Clear the IMASKK bit.
1. Configure the keyboard pins as outputs by setting the appropriate
2. Write logic 1s to the appropriate data register bits.
3. Enable the KBI pins by setting the appropriate KBIEx bits in the
Freescale Semiconductor, Inc.
For More Information On This Product,
keyboard status and control register.
keyboard interrupt enable register.
to clear any false interrupts.
DDR bits in data direction register.
keyboard interrupt enable register.
Keyboard Interrupt Module (KBI)
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Keyboard Interrupt Module (KBI)
Functional Description
Data Sheet
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