MC68HC908GR16 Datasheet, PDF (112/310 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Keyboard Interrupt Module (KBI)
NOTE:
another interrupt request. If the keyboard interrupt mask bit, IMASKK, is
clear, the CPU loads the program counter with the vector address at
locations $FFE0 and $FFE1.
• Return of all enabled keyboard interrupt pins to logic 1 — As long as any
enabled keyboard interrupt pin is at logic 0, the keyboard interrupt remains
set.
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 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.
9.4 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.
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.
Data Sheet
112
Keyboard Interrupt Module (KBI)
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MC68HC908GR16 — Rev. 1.0
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