MC68HC08XL36 Datasheet, PDF (313/362 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Initialization
Freescale Semiconductor, Inc.
Keyboard Interrupt Module (KBI)
Initialization
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:
1. Mask keyboard interrupts by setting the IMASKK bit in the
keyboard status and control register.
2. Enable the KBI pins by setting the appropriate KBIEx bits in the
keyboard interrupt enable register.
3. Write to the ACKK bit in the keyboard status and control register
to clear any false interrupts.
4. Clear the IMASKK bit.
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. Configure the keyboard pins as outputs by setting the appropriate
DDRD bits in data direction register D.
2. Write logic 1s to the appropriate port D data register bits.
3. Enable the KBI pins by setting the appropriate KBIEx bits in the
keyboard interrupt enable register.
5-intkbd8_a
MOTOROLA
Keyboard Interrupt Module (KBI)
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MC68HC08XL36
313