NXP Semiconductors MC9S08LG16, Reference Manual

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Chapter 7 Keyboard Interrupt (S08KBIV2)
MC9S08LG32 MCU Series, Rev. 5
Freescale Semiconductor 133
7.4 Functional Description
This on-chip peripheral module is called a keyboard interrupt (KBI) module because originally it was
designed to simplify the connection and use of row-column matrices of keyboard switches. However, these
inputs are also useful as extra external interrupt inputs and as an external means of waking the MCU from
stop or wait low-power modes.
The KBI module allows up to eight pins to act as additional interrupt sources. Writing to the KBIPEn bits
in the keyboard interrupt pin enable register (KBIPE) independently enables or disables each KBI pin.
Each KBI pin can be configured as edge sensitive or edge and level sensitive based on the KBMOD bit in
the keyboard interrupt status and control register (KBISC). Edge sensitive can be software programmed to
be either falling or rising; the level can be either 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 (KBIES).
Synchronous logic is used to detect edges. Prior to detecting an edge, enabled keyboard inputs must be at
the deasserted logic level. A falling edge is detected when an enabled keyboard 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.
7.4.1 Edge Only Sensitivity
A valid edge on an enabled KBI pin will set KBF in KBISC. If KBIE in KBISC is set, an interrupt request
will be presented to the CPU. Clearing of KBF is accomplished by writing a 1 to KBACK in KBISC.
7.4.2 Edge and Level Sensitivity
A valid edge or level on an enabled KBI pin will set KBF in KBISC. If KBIE in KBISC is set, an interrupt
request will be presented to the CPU. Clearing of KBF is accomplished by writing a 1 to KBACK in
KBISC provided all enabled keyboard inputs are at their deasserted levels. KBF will remain set if any
enabled KBI pin is asserted while attempting to clear by writing a 1 to KBACK.
7 6 5 4 3 2 1 0
R
KBEDG7 KBEDG6 KBEDG5 KBEDG4 KBEDG3 KBEDG2 KBEDG1 KBEDG0
W
Reset: 0 0 0 0 0 0 0 0
Figure 7-5. KBI Edge Select Register
Table 7-5. KBIES Register Field Descriptions
Field Description
7:0
KBEDGn
Keyboard Edge Selects — Each of the KBEDGn bits selects the falling edge/low level or rising edge/high level
function of the corresponding pin).
0 Falling edge/low level.
1 Rising edge/high level.