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MC908QC8CDXER Datasheet(PDF) 88 Page - Freescale Semiconductor, Inc |
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MC908QC8CDXER Datasheet(HTML) 88 Page - Freescale Semiconductor, Inc |
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88 / 274 page  Keyboard Interrupt Module (KBI) MC68HC908QC16 • MC68HC908QC8 • MC68HC908QC4 Data Sheet, Rev. 2 88 Freescale Semiconductor The keyboard flag bit (KEYF) in KBSCR can be read to check for pending interrupts. The KEYF bit is not affected by IMASKK, which makes it useful in applications where polling is preferred. NOTE 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. 8.3.2 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. 8.4 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. 8.5 Low-Power Modes The WAIT and STOP instructions put the MCU in low power-consumption standby modes. 8.5.1 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. 8.5.2 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. |
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