s908qc16vdse Freescale Semiconductor, Inc, s908qc16vdse Datasheet - Page 88

• Manufacturer Part Number: s908qc16vdse
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

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.
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:
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:
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.
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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.
•
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.
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.
MC68HC908QC16 • MC68HC908QC8 • MC68HC908QC4 Data Sheet, Rev. 4
NOTE
Freescale Semiconductor