mc68hc908ld64 Freescale Semiconductor, Inc, mc68hc908ld64 Datasheet - Page 325

• Manufacturer Part Number: mc68hc908ld64
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

21.6 Keyboard Initialization
21.7 I/O Registers
MC68HC908LD64
Freescale Semiconductor
—
Rev. 3.0
When a keyboard interrupt pin is enabled, it takes time for the pull-up
device 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:
These registers control and monitor operation of the keyboard module:
1. Mask keyboard interrupts by setting the IMASKK bit in the
2. Enable the KBI pins by setting the appropriate KBIEx bits in the
3. Write to the ACKK bit in the keyboard status and control register
4. Clear the IMASKK bit.
1. Configure the keyboard pins as outputs by setting the appropriate
2. Write logic 1s to the appropriate port A data register bits.
3. Enable the KBI pins by setting the appropriate KBIEx bits in the
•
•
keyboard status and control register.
keyboard interrupt enable register.
to clear any false interrupts.
DDRA bits in data direction register A.
keyboard interrupt enable register.
Keyboard status and control register (KBSCR)
Keyboard interrupt enable register (KBIER)
Keyboard Interrupt Module (KBI)
Keyboard Interrupt Module (KBI)
Keyboard Initialization
Data Sheet
325