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MC908QT2 Datasheet(PDF) 81 Page - Freescale Semiconductor, Inc |
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MC908QT2 Datasheet(HTML) 81 Page - Freescale Semiconductor, Inc |
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81 / 184 page  Functional Description MC68HC908QY/QT Family Data Sheet, Rev. 6 Freescale Semiconductor 81 Figure 9-2. Keyboard Interrupt Block Diagram If the MODEK bit is set, the keyboard interrupt inputs are both falling edge and low-level sensitive, and both of the following actions must occur to clear a keyboard interrupt request: • Vector fetch or software clear — A vector fetch generates an interrupt acknowledge signal to clear the interrupt request. Software may generate the interrupt acknowledge signal by writing a 1 to the ACKK bit in the keyboard status and control register (KBSCR). The ACKK bit is useful in applications that poll the keyboard interrupt inputs and require software to clear the keyboard interrupt request. Writing to the ACKK bit prior to leaving an interrupt service routine can also prevent spurious interrupts due to noise. Setting ACKK does not affect subsequent transitions on the keyboard interrupt inputs. A falling edge that occurs after writing to the ACKK bit latches another interrupt request. If the keyboard interrupt mask bit, IMASKK, is clear, the central processor unit (CPU) loads the program counter with the vector address at locations $FFE0 and $FFE1. • Return of all enabled keyboard interrupt inputs to logic 1 — As long as any enabled keyboard interrupt pin is at logic 0, the keyboard interrupt remains set. The auto wakeup interrupt input, AWUIREQ, will be cleared only by writing to ACKK bit in KBSCR or reset. The vector fetch or software clear and the return of all enabled keyboard interrupt pins to logic 1 may occur in any order. If the MODEK bit is clear, the keyboard interrupt pin is falling-edge sensitive only. With MODEK clear, a vector fetch or software clear immediately clears the keyboard interrupt request. Reset clears the keyboard interrupt request and the MODEK bit, clearing the interrupt request even if a keyboard interrupt input stays at logic 0. The keyboard flag bit (KEYF) in the keyboard status and control register can be used to see if a pending interrupt exists. The KEYF bit is not affected by the keyboard interrupt mask bit (IMASKK) which makes it useful in applications where polling is preferred. KBIE0 KBIE5 . . . DQ CK CLR VDD MODEK IMASKK KEYBOARD INTERRUPT FF VECTOR FETCH DECODER ACKK INTERNAL BUS RESET KBI5 KBI0 SYNCHRONIZER KEYF KEYBOARD INTERRUPT REQUEST TO PULLUP ENABLE AWUIREQ(1) TO PULLUP ENABLE 1. For AWUGEN logic refer to Figure 4-1. Auto Wakeup Interrupt Request Generation Logic. |
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