Kbi Pullup Resistor - NXP Semiconductors MC9S08SU16 Reference Manual

15.6.3 KBI Pullup Resistor

Each KBI pin, if enabled by KBI_PE, can be configured via the associated I/O port pull
enable register, see chapter, to use:
• an internal pullup resistor, or
• no resistor
If an internal pullup resistor is enabled for an enabled KBI pin, the associated I/O port
pull select register (see I/O Port chapter) can be used to select an internal pullup resistor.
15.6.4 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
should do the following:
1. Mask keyboard interrupts by clearing KBI_SC[KBIE].
2. Enable the KBI polarity by setting the appropriate KBI_ES[KBEDGn] bits.
3. Before using internal pullup resistors, configure the associated bits in PORT_.
4. Enable the KBI pins by setting the appropriate KBI_PE[KBIPEn] bits.
5. Write to KBI_SC[KBACK] to clear any false interrupts.
6. Set KBI_SC[KBIE] to enable interrupts.
NXP Semiconductors
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
Chapter 15 Keyboard Interrupts (KBI)
241