mc68hc908sr12 Freescale Semiconductor, Inc, mc68hc908sr12 Datasheet - Page 347

• Manufacturer Part Number: mc68hc908sr12
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

20.5.1 Keyboard Initialization
20.6 Keyboard Interrupt Registers
MC68HC908SR12•MC68HC08SR12 — Rev. 5.0
Freescale Semiconductor
When a keyboard interrupt pin is enabled, it takes time for the internal
pull-up 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:
Two registers control the operation of the keyboard interrupt 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 data register bits.
3. Enable the KBI pins by setting the appropriate KBIEx bits in the
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keyboard status and control register.
keyboard interrupt enable register.
to clear any false interrupts.
DDR bits in data direction register.
keyboard interrupt enable register.
Keyboard Status and Control Register — $001A
Keyboard Interrupt Enable Register — $001B
Keyboard Interrupt Module (KBI)
Keyboard Interrupt Module (KBI)
Keyboard Interrupt Registers
Data Sheet
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