NXP Semiconductors MC9S08LG16, Reference Manual

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Chapter 7 Keyboard Interrupt (S08KBIV2)
MC9S08LG32 MCU Series, Rev. 5
134 Freescale Semiconductor
7.4.3 KBI Pullup/Pulldown Resistors
The KBI pins can be configured to use an internal pullup/pulldown resistor using the associated I/O port
pullup enable register. If an internal resistor is enabled, the KBIES register is used to select whether the
resistor is a pullup (KBEDGn = 0) or a pulldown (KBEDGn = 1).
7.4.4 KBI Initialization
When a keyboard interrupt pin is first enabled it is possible to get a false keyboard interrupt flag. To
prevent a false interrupt request during keyboard initialization, the user must do the following:
1. Mask keyboard interrupts by clearing KBIE in KBISC.
2. Enable the KBI polarity by setting the appropriate KBEDGn bits in KBIES.
3. If using internal pullup/pulldown device, configure the associated pullup enable bits in PTxPE.
4. Enable the KBI pins by setting the appropriate KBIPEn bits in KBIPE.
5. Write to KBACK in KBISC to clear any false interrupts.
6. Set KBIE in KBISC to enable interrupts.