mc68hc908qf4 Freescale Semiconductor, Inc, mc68hc908qf4 Datasheet - Page 83

• Manufacturer Part Number: mc68hc908qf4
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

9.3.2 Keyboard Initialization
9.4 Wait Mode
9.5 Stop Mode
9.6 Keyboard Module During Break Interrupts
MC68HC908QF4 — Rev. 1.0
MOTOROLA
When a keyboard interrupt pin is enabled, it takes time for the internal pullup to
reach a logic 1. 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-triggered pin can be acknowledged immediately
after enabling the pin. An interrupt signal on an edge- and level-triggered interrupt
pin must be acknowledged after a delay that depends on the external load.
Another way to avoid a false interrupt:
The keyboard module remains active in wait mode. Clearing the IMASKK bit in the
keyboard status and control register enables keyboard interrupt requests to bring
the MCU out of wait mode.
The keyboard module remains active in stop mode. Clearing the IMASKK bit in the
keyboard status and control register enables keyboard interrupt requests to bring
the MCU out of stop mode.
The system integration module (SIM) controls whether the keyboard interrupt latch
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.
To allow software to clear the keyboard interrupt latch during a break interrupt,
write a 1 to the BCFE bit. If a latch is cleared during the break state, it remains
cleared when the MCU exits the break state.
1. Mask keyboard interrupts by setting the IMASKK bit in the keyboard status
2. Enable the KBI pins by setting the appropriate KBIEx bits in the keyboard
3. Write to the ACKK bit in the keyboard status and control register to clear any
4. Clear the IMASKK bit.
1. Configure the keyboard pins as outputs by setting the appropriate DDRA
2. Write 1s to the appropriate port A data register bits.
3. Enable the KBI pins by setting the appropriate KBIEx bits in the keyboard
and control register.
interrupt enable register.
false interrupts.
bits in the data direction register A.
interrupt enable register.
Freescale Semiconductor, Inc.
For More Information On This Product,
Keyboard Interrupt Module (KBI)
Go to: www.freescale.com
Keyboard Interrupt Module (KBI)
Wait Mode
Data Sheet
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