MC68HC908JK3 MOTOROLA [Motorola, Inc], MC68HC908JK3 Datasheet - Page 168

• Manufacturer Part Number: MC68HC908JK3
• Description: MC68HC908JK1
• Manufacturer: MOTOROLA [Motorola, Inc]

Keyboard Interrupt Module (KBI)
14.4.1 Keyboard Initialization
Technical Data
168
NOTE:
If the MODEK bit is clear, the keyboard interrupt pin is falling-edge-
sensitive only. With MODEK clear, a vector fetch or software clear
immediately clears the keyboard interrupt request.
Reset clears the keyboard interrupt request and the MODEK bit, clearing
the interrupt request even if a keyboard interrupt pin stays at logic 0.
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, disable the pull-
up device, use the data direction register to configure the pin as an input
and then 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
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.
keyboard status and control register.
keyboard interrupt enable register.
to clear any false interrupts.
Keyboard Interrupt Module (KBI)
MC68H(R)C908JL3
MOTOROLA
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Rev. 1.0