MC68HC908QC16_07 Datasheet, PDF (88/274 Pages) Freescale Semiconductor, Inc – Microcontrollers

Keyboard Interrupt Module (KBI)
The keyboard flag bit (KEYF) in KBSCR can be read to check for pending interrupts. The KEYF bit is not
affected by IMASKK, which makes it useful in applications where polling is preferred.
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 0 for software to read the
pin.
8.3.2 Keyboard Initialization
When a keyboard interrupt pin is enabled, it takes time for the internal pullup or pulldown device to pull
the pin to its deasserted level. 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 IMASKK in KBSCR.
2. Enable the KBI polarity by setting the appropriate KBIPx bits in KBIPR.
3. Enable the KBI pins by setting the appropriate KBIEx bits in KBIER.
4. Write to ACKK in KBSCR to clear any false interrupts.
5. Clear IMASKK.
An interrupt signal on an edge sensitive pin can be acknowledged immediately after enabling the pin. An
interrupt signal on an edge and level sensitive pin must be acknowledged after a delay that depends on
the external load.
8.4 Interrupts
The following KBI source can generate interrupt requests:
• Keyboard flag (KEYF) — The KEYF bit is set when any enabled KBI pin is asserted based on the KBI
mode and pin polarity. The keyboard interrupt mask bit, IMASKK, is used to enable or disable KBI
interrupt requests.
8.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
8.5.1 Wait Mode
The KBI module remains active in wait mode. Clearing IMASKK in KBSCR enables keyboard interrupt
requests to bring the MCU out of wait mode.
8.5.2 Stop Mode
The KBI module remains active in stop mode. Clearing IMASKK in KBSCR enables keyboard interrupt
requests to bring the MCU out of stop mode.
MC68HC908QC16 • MC68HC908QC8 • MC68HC908QC4 Data Sheet, Rev. 3
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Freescale Semiconductor