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MCF51QE128 MCU Series Reference Manual, Rev. 3
Freescale Semiconductor 117
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Chapter 6 Parallel Input/Output Control
Figure 6-3. Port Interrupt Block Diagram
Writing to the KBIPEn bits in the keyboard x interrupt pin enable register (KBIxPE) independently enables
or disables each port pin. Each port can be configured as edge sensitive or edge and level sensitive based
on KBIxSC[KBIMOD]. Edge sensitivity can be software programmed to be falling or rising; the level can
be low or high. The polarity of the edge or edge and level sensitivity is selected using the KBEDGn bits
in the keyboard interrupt edge select register (KBIxES).
Synchronous logic detects edges. Prior to detecting an edge, enabled port inputs must be at the deasserted
logic level. A falling edge is detected when an enabled port input signal is seen as a logic 1 (the deasserted
level) during one bus cycle and then a logic 0 (the asserted level) during the next cycle. A rising edge is
detected when the input signal is seen as a logic 0 during one bus cycle and then a logic 1 during the next
cycle.
6.5.1 Edge Only Sensitivity
A valid edge on an enabled port pin sets KBIxSC[KBF]. If the KBIxSC[KBIE] bit is set, an interrupt
request is generated to the CPU. Clearing of KBF is accomplished by writing a 1 to KBIxSC[KBACK].
6.5.2 Edge and Level Sensitivity
A valid edge or level on an enabled port pin sets KBIxSC[KBF]. If KBIxSC[KBIE] is set, an interrupt
request is generated to the CPU. Clearing of KBF is accomplished by writing a 1 to KBIxSC[KBACK],
provided all enabled port inputs are at their deasserted levels. KBF remains set if any enabled port pin is
asserted while attempting to clear by writing a 1 to KBACK.
6.5.3 Pull-up/Pull-down Resistors
The keyboard interrupt pins can be configured to use an internal pull-up/pull-down resistor using the
associated I/O port pull-up enable register. If an internal resistor is enabled, the KBIxES register selects
whether the resistor is a pull-up (KBEDGn = 0) or a pull-down (KBEDGn =1).
KBEDGn
DQ
CK
CLR
VDD
KBIMOD
KBIE
KEYBOARD
INTERRUPT FF
KBACK
RESET
SYNCHRONIZER
KBF
STOP BYPASS
STOP
BUSCLK
KBIPEn
0
1
S
KBIPE0
0
1
S
KBEDG0
KBIxP0
KBIxPn
KBI
INTERRUPT
REQUEST