NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
FXTH87ERM
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Reference manual
Rev. 5.0 — 4 February 2019
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= Reserved
Table 73. KBIES register field descriptions
Field
Description
3:0
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.
9.6 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 KBIPE[3:0] 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 KBEDG[3:0] 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 reset logic level. A falling edge is detected when an enabled
keyboard input signal is seen as a logic 1 (the reset 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.
9.6.1 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.
9.6.2 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 reset
levels. KBF will remain set if any enabled KBI pin is asserted while attempting to clear by
writing a 1 to KBACK.
9.6.3 KBI pullup/pulldown resistors
The KBI pins can be configured to use an internal pullup/pulldown resistor using the
associated I/O port pullup enable register. If an internal resistor is enabled, the KBIES
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