MC68HC908GR8CD Freescale Semiconductor, MC68HC908GR8CD Datasheet - Page 123

• Manufacturer Part Number: MC68HC908GR8CD
• Description: 8-bit Microcontrollers - MCU 8 Bit 8MHz
• Manufacturer: Freescale Semiconductor

Specifications of MC68HC908GR8CD

• Product Category: 8-bit Microcontrollers - MCU
• Rohs: yes
• Core: HC08
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 8 MHz
• Program Memory Size: 64 KB
• Data Ram Size: 384 B
• Operating Supply Voltage: 3 V to 5 V
• Package / Case: SOIC-28
• Mounting Style: SMD/SMT
• Data Rom Size: 64 KB
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Number Of Programmable I/os: 21
• Program Memory Type: Flash

To determine the logic level on a keyboard interrupt pin, use the data direction register to configure the
pin as an input and read the data register.
13.4 Keyboard Initialization
When a keyboard interrupt pin is enabled, it takes time for the internal pullup to reach a 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 is:
13.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
13.5.1 Wait Mode
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.
13.5.2 Stop 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.
13.6 Keyboard Module During Break Interrupts
The system integration module (SIM) controls whether the keyboard interrupt latch can be cleared during
the break state. The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear
status bits during the break state.
Freescale Semiconductor
1. Mask keyboard interrupts by setting the IMASKK bit in the keyboard status and control register.
2. Enable the KBI pins by setting the appropriate KBIEx bits in the keyboard interrupt enable register.
3. Write to the ACKK bit in the keyboard status and control register to clear any false interrupts.
4. Clear the IMASKK bit.
1. Configure the keyboard pins as outputs by setting the appropriate DDRA bits in data direction
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 interrupt enable register.
register A.
Setting a keyboard interrupt enable bit (KBIEx) forces the corresponding
keyboard interrupt pin to be an input, overriding the data direction register.
However, the data direction register bit must be a 0 for software to read the
pin.
MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7
NOTE
Keyboard Initialization
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