MC68HC908RK2 Datasheet, PDF (189/232 Pages) Motorola, Inc – Microcontroller Unit

Keyboard/External Interrupt Module (KBI)
Functional Description
The vector fetch or software clear and the return of all enabled keyboard
interrupt pins to logic 1 may occur in any order.
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 IRQ and 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.
NOTE:
Setting a keyboard interrupt enable bit (KBIE<x>) 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.
14.4.5 Keyboard 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.
MC68HC908RK2 — Rev. 4.0
MOTOROLA
Keyboard/External Interrupt Module (KBI)
Advance Information
189