NXP Semiconductors UM11227 - LVD Interrupt Operation; Low-Voltage Warning (LVW); System Clock Control; Keyboard Interrupts

NXP Semiconductors
UM11227
NTM88 family of tire pressure monitor sensors
UM11227 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2020. All rights reserved.
User manual Rev. 6 — 24 April 2020
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10.4.3 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 is set and an LVD
interrupt occurs.
10.4.4 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.
10.5 System clock control
Several clock rate selections are possible with the NTM88 using the BUSCLKS[1:0]
control bits to select the clock frequency division of the HFO as given in Table 18. These
bits are cleared by any MCU reset.
Table 18. HFO frequency selections
BUSCLKS1 BUSCLKS0
HFO Frequency
(MHz)
CPU Bus
Frequency (MHz)
0 0 8 4
0 1 4 2
1 0 2 1
1 1 1 0.5
10.6 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 19.
Note: Regarding wake-up from Stop1, the reset vector is accessed, taking precedence
over the interrupt vector.
Table 19. Keyboard interrupt assignments
KBI Pin Pin Function
0 PTA0 General I/O
1 PTA1 General I/O
2 PTA2 General I/O
3 PTA3 General I/O
10.7 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 wake-up