NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
7.6.3 LVD interrupt operation
When a low voltage condition is detected and the LVD circuit is configured for interrupt
operation (LVDE set, LVDIE set, and LVDRE clear), then LVDF will be set and an LVD
interrupt will occur.
7.6.4 Low-Voltage Warning (LVW)
The LVD system has a low voltage warning flag, LVWF, to indicate to the user that the
supply voltage is approaching, but is still above, the LVD reset voltage. The LVWF can
be reset by writing a logical one to the LVWACK bit. The LVW does not have an interrupt
associated with it. There are two user selectable trip voltages for the LVW as selected
by LVWV in SPMSC3. The LVWF is set when the supply voltage falls below the selected
level and cannot be reset until the supply voltage has risen above the selected level. The
threshold for falling and rising differ by a small amount of hysteresis.
7.7 System clock control
Several clock rate selections are possible with the FXTH87E using the BUSCLKS[1:0]
control bits to select the clock frequency division of the HFO as given in Table 32. These
bits are cleared by any MCU reset.
Table 32.ꢀHFO frequency selections
HFO Frequency
(MHz)
CPU Bus
Frequency (MHz)
BUSCLKS1
BUSCLKS0
0
0
1
1
0
1
0
1
8
4
2
1
4
2
1
0.5
7.8 Keyboard interrupts
The keyboard interrupts can be used to wake the MCU. These are assigned to specific
general I/O pins as given in Table 33.
Note: Regarding wake-up from Stop1, the reset vector is accessed, taking precedence
over the interrupt vector.
Table 33.ꢀKeyboard interrupt assignments
KBI
0
Pin
Pin Function
General I/O
General I/O
General I/O
General I/O
PTA0
PTA1
PTA2
PTA3
1
2
3
7.9 Real-time interrupt
The RTI uses the internal low frequency oscillator (LFO) as its clock source. The RTI can
be used as a periodic interrupt in MCU RUN mode, or can be used as a periodic wakeup
FXTH87ERM
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Reference manual
Rev. 5.0 — 4 February 2019
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