MC908QY8CDWE Datasheet, PDF (88/232 Pages) Freescale Semiconductor, Inc – Addendum to MC68HC908QB8, rev. 3

Keyboard Interrupt Module (KBI)
9.3.2 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.
9.4 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.
9.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
9.5.1 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.
9.5.2 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.
9.6 KBI During Break Interrupts
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. The BCFE bit in the break flag control register (BFCR) enables software to clear status
bits during the break state. See BFCR in the SIM section of this data sheet.
To allow software to clear status bits during a break interrupt, write a 1 to BCFE. If a status bit is cleared
during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a 0 to BCFE. With BCFE cleared (its default state),
software can read and write registers during the break state without affecting status bits. Some status bits
have a two-step read/write clearing procedure. If software does the first step on such a bit before the
break, the bit cannot change during the break state as long as BCFE is cleared. After the break, doing the
second step clears the status bit.
MC68HC908QB8 Data Sheet, Rev. 3
86
Freescale Semiconductor