XC908AS60ACFU Motorola Semiconductor Products, XC908AS60ACFU Datasheet - Page 435

• Manufacturer Part Number: XC908AS60ACFU
• Description: MC68HC908AZ60A, MC68HC908AS60A Hcmos Microcontroller Unit Technical Data
• Manufacturer: Motorola Semiconductor Products

24.5 Keyboard Initialization
MC68HC908AZ60A — Rev 2.0
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. Configure the keyboard pins as outputs by setting the appropriate
3. Write logic 1s to the appropriate port G and port H data register
4. 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
DDRG bits in data direction register G.
DDRH bits in data direction register H.
bits.
keyboard interrupt enable register.
Keyboard Module (KBD)
Keyboard Module (KBD)
Keyboard Initialization
Technical Data
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