MC68HC908AP16CFA MOTOROLA [Motorola, Inc], MC68HC908AP16CFA Datasheet - Page 390

• Manufacturer Part Number: MC68HC908AP16CFA
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Keyboard Interrupt Module (KBI)
20.4.1 Keyboard Initialization
Data Sheet
390
NOTE:
The keyboard flag bit (KEYF) in the keyboard status and control register
can be used to see if a pending interrupt exists. The KEYF bit is not
affected by the keyboard interrupt mask bit (IMASKK) which makes it
useful in applications where polling is preferred.
To determine the logic level on a keyboard interrupt pin, use the data
direction register to configure the pin as an input and read the data
register.
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
pull-up 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
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.
Go to: www.freescale.com
MC68HC908AP Family — Rev. 2.5
MOTOROLA