mc9s08qg8 Freescale Semiconductor, Inc, mc9s08qg8 Datasheet - Page 179

• Manufacturer Part Number: mc9s08qg8
• Description: Hcs08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Synchronous logic is used to detect edges. Prior to detecting an edge, enabled keyboard inputs must be at
the deasserted logic level. A falling edge is detected when an enabled keyboard input signal is seen as a
logic 1 (the deasserted level) during one bus cycle and then a logic 0 (the asserted level) during the next
cycle. A rising edge is detected when the input signal is seen as a logic 0 during one bus cycle and then a
logic 1 during the next cycle.
12.4.1
A valid edge on an enabled KBI pin will set KBF in KBISC. If KBIE in KBISC is set, an interrupt request
will be presented to the CPU. Clearing of KBF is accomplished by writing a 1 to KBACK in KBISC.
12.4.2
A valid edge or level on an enabled KBI pin will set KBF in KBISC. If KBIE in KBISC is set, an interrupt
request will be presented to the CPU. Clearing of KBF is accomplished by writing a 1 to KBACK in
KBISC provided all enabled keyboard inputs are at their deasserted levels. KBF will remain set if any
enabled KBI pin is asserted while attempting to clear by writing a 1 to KBACK.
12.4.3
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).
12.4.4
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:
Freescale Semiconductor
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.
Edge Only Sensitivity
Edge and Level Sensitivity
KBI Pullup/Pulldown Resistors
KBI Initialization
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 1.01
Keyboard Interrupt (S08KBIV2)
179