MC68HC908KX2 MOTOROLA [Motorola, Inc], MC68HC908KX2 Datasheet - Page 175

• Manufacturer Part Number: MC68HC908KX2
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

13.5 Keyboard Initialization
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 — Rev. 1.0
MOTOROLA
When a keyboard interrupt pin is enabled, the pin may initially be low and
cause a false interrupt to occur. A false interrupt on an edge-triggered
pin can be acknowledged immediately after enabling the pin. A false
interrupt on an edge- and level-triggered interrupt pin must be
acknowledged after the pin has been pulled high.
The internal pullup device, the pin capacitance, as well as the external
load will factor into the actual amount of time it takes for the pin to pull
high. Considering only an internal pullup of 48 k and pin capacitance
of 8 pF, the pullup time will be on the order of 1 s.
To prevent a false interrupt on keyboard initialization:
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 port A data register bits.
3. Enable the KBI pins by setting the appropriate KBIEx bits in the
keyboard status and control register.
keyboard interrupt enable register.
to clear any false interrupts.
DDRA bits in data direction register A.
keyboard interrupt enable register.
Keyboard Interrupt Module (KBI)
Keyboard Interrupt Module (KBI)
Keyboard Initialization
Technical Data
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